This document contains Chapters 36 to 38 CHAPTER 36 ANIMAL BEHAVIOR CHAPTER OUTLINE 36.1. Science of Animal Behavior A. Ethology (Figure 36.1) 1. The study of animal behavior as a science had its roots in the 1872 work of Charles Darwin. 2. Questions about how animals behave ask about physiological functions or proximate causation. 3. Questioning why animals behave a certain way as selected adaptations asks about ultimate causation. 4. Comparative psychology attempts to find general laws of behavior that apply across species. 5. Ethology is the science of animal behavior in the animal’s natural habitat. 6. A central theme of ethology is that behavioral traits can be isolated and measured and they have evolutionary histories. 7. Sociobiology is the ethological study of social behavior and originated with E.O. Wilson’s 1975 book. 8. Social behavior is reciprocal communication of a cooperative nature that permits a group of organisms of the same species to become organized and is represented by four “pinnacles.” a. Colonial invertebrates, such as the Portuguese man-of-war, are tightly knit composites of interdependent individual organisms. b. Social insects such as ants, bees and termites have developed sophisticated systems of communication. c. Dolphins, elephants and some primates have highly developed social systems. d. Humans have a unique social behavior. 9. Behavioral ecology focuses on individual behavior that maximizes reproductive and evolutionary success and studies mate choice, foraging, parental investment, etc. 10. Much of the work by comparative psychologists and ethologists can be found under the discipline of behavioral ecology rather than sociobiology. 36.2. Describing Behavior: Principles of Classical Ethology (Figures 36.2–36.4) A. Early Work 1. The work of Konrad Lorenz and Niko Tinbergen laid down basic concepts in animal behavior. 2. What appears to be rational retrieval of an egg by a goose can be a “fixed pattern” behavior. 3. Such predictable sequences are called stereotypical behaviors. 4. Lorenz labeled any stimulus that triggered a certain innate behavior as a releaser. 5. If the animal responded to just one specific aspect of the releaser, this was a sign stimulus. 6. As an example, an alarm call of an adult bird may release a freeze response in a chick. 7. Tinbergen’s male stickleback fish became aggressive at the sign of another male’s red flank. 8. These automatic programmed responses are most efficient in wild conditions that do not pose the unusual and artificial conditions set up by the researchers. 9. Behavioral syndromes are suites of correlated behaviors reflecting between-individual consistency in behavior across multiple situations. 36.3. Control of Behavior A. Innate Behavior 1. Invariable and predictable stereotyped behaviors are inherited or innate. 2. Instinctive behaviors are dependent on interactions between an organism and its environment during ontogeny. 2. Although the behavior is independent of learning, it depends on interactions during development. 3. Programmed behavior is important for survival, especially when animals do not know their parents. 4. Programmed behavior can equip an animal for immediate response to the world at birth or hatching. 5. More complex animals with longer lives have more time for social interactions and learning. B. Genetics of Behavior (Figures 36.5, 36.6) 1. Hereditary transmission of most innate behaviors is complex with many interacting genes. 2. However, some behavioral differences within species show simple Mendelian transmission. 3. Honeybee Hygiene a. Honeybees are susceptible to a bacterial disease called American foulbrood. b. If bees remove the dead larvae from the hive, they reduce the chance of infection spreading. c. A strain of bees, called “hygienic,” uncaps cells containing rotten larvae and carries them out. d. The two components of the behavior are removal of cell caps and removal of larvae. e. Individuals homozygous for a recessive allele u at one gene perform uncapping behavior. f. Individuals homozygous for recessive allele r at a second gene perform removal behavior. g. Hygienic bees were crossed with nonhygienic bees; all heterozygous hybrids were nonhygienich. A backcross with hygienic strains produced a one-quarter hygienic portion, one-quarter that did not uncap but would remove bees, and one-quarter that uncapped but did not remove dead larvae. 4. Most inherited behaviors do not show simple segregation, but show an intermediate behavior. 5. Cross-breeding of lovebirds that carried nest material either in the beak or in the feathers produced hybrids that had a confused carrying behavior. C. Learning and the Diversity of Behavior (Figures 36.7, 36.8) 1. Learning is the modification of behavior through experience. 2. The marine opisthobranch snail Aplysia is an excellent experimental animal for learning. a. When its siphon is prodded, the snail withdraws its gills for protection. b. If repeatedly prodded, it soon ignores the stimulus, a behavior modification called habituation. c. If a noxious stimulus is added to the prodding, it is sensitized and rapidly withdraws its gills. d. These behaviors have been traced to nervous pathways, connecting sensory neurons to motor neurons that control the withdrawal muscles. e. Repeated stimulations diminished release of synaptic transmitter from sensory neurons. f. Sensory neurons continued to fire, but with less neurotransmitter the system was less responsive. g. Sensitization involved action of a facilitating neuron that was stimulated by the noxious agent and increased the amount of transmitter released by the siphon sensory neurons. h. This study showed that strengthening or weakening the gill-withdrawal reflex involved changes in the levels of transmitter in existing synapses. 3. More complex kinds of learning may involve formation of new neural pathways and connections as well as changes in existing circuits. 4. Imprinting (Figures 36.9, 36.10) a. Imprinting imposes a stable behavior in a young animal by exposure to particular stimuli during a critical period in development. b. A newly hatched or duckling follows its mother; if isolated, it follows the first large object it sees. c. Konrad Lorenz hand-reared goslings and they imprinted on him. d. There is only a brief sensitive period when imprinting can occur; the bond then lasts for life. 5. Bird Songs Learned During a “Critical Window” a. Songbirds demonstrate robust sex differences in many aspects of behavior. b. The songs of sparrows are important territorial calls and rely partially on learning. c. If a baby bird is reared in isolation, it sings a rudimentary song. d. The sparrow must hear a normal bird song in a critical period 10–50 days after hatching. e. However, the young sparrow does not learn the songs of other species of birds during this time. f. We can also see the complex interaction of learned and innate factors in the navigation of seasonally migratory birds. 36.4. Social Behavior (Figure 36.11) A. Definitions 1. Any response of one animal to another animal of the same species is a social behavior. 2. Two rival males fighting for possession of a female is a social interaction. 3. Moths swarming around a light, or trout in a cold portion of a stream are not social behaviors, but are merely individuals responding to an environmental cue. 4. Social aggregations depend upon signals from the animals themselves. 5. Among some animals, breeding may be the only adult social behavior. 6. Other animals form strong monogamous relationships for life. 7. Mother mammals and birds often form social bonds with their young until they are fledged or weaned. B. Selective Consequences of Sociality (Figures 36.12, 36.13) 1. Social aggregations provide both passive and active defense; they are safer in a group than they are alone. 2. In a breeding colony of gulls, an alarm call brings many to attack the predator en masse. 3. Prairie dogs live in a loose group and benefit from the extra eyes, ears and noses of others for warning. 4. The more animals there are in a group, the less likely an individual within the group will be eaten. 5. Sociality brings together males and females and synchronizes reproductive behavior. 6. In colonial birds, the sounds and displays trigger pre-reproduction endocrine changes in the birds. 7. Living in close quarters, a bird colony conspires to defend young and increase survival. 8. Social organization also benefits in cooperation in hunting for food, huddling for mutual protection from severe weather, opportunities for division of labor and the potential for learning and transmitting useful information through the society. 9. Transfer of innovative behaviors is illustrated in the case of Imo and fellow macaques on a Japanese beach; her discoveries of washing potatoes and wheat-sifting soon became common in the troop. 10. Acquisition of food-cleaning skills by Imo and her peers shows that social setting provides opportunites for acquisition and sharing of complex learned behaviors. 11. Social living has disadvantages. a. Camouflaged individuals survive predators by being dispersed. b. Large predators need large amounts of food. c. The ecological situation determines if a solitary or social strategy is better. 12. In socially coordinated behavior an individual adjusts its actions to presence of others to increase directly its own reproductive sucess. 13. In cooperative behavior the individual performs activities that benefit others because such behavior ultimately benefits the individual’s genetic contribution to future generations. C. Antagonistic or Competitive Behavior (Figures 36.14–36.16) 1. There is competition for food, sexual mates, or shelter when any of these are limited. 2. Aggression is an offensive physical action, or threat, to force others to abandon something. 3. Agonistic behaviors are a broader category including any activity related to fighting. 4. Animals reserve their dangerous weapons for securing prey and do not use them on their own species. 5. Animal aggression within a species involves symbolic or ritualized displays that avoid injury or death. 6. A ritualized display is a behavior that has been modified through evolution to make it effective in serving a communicative function. 7. A wide array of animal “fights” involve ritual jousts: fiddler crab claw battles, male rattlesnake dances, puffing fish, giraffe “necking,” and bighorn sheep butting heads. 8. The loser of a ritualized battle often runs away or signals defeat by a subordination ritual. 9. The victor in such competition has access to the contested food, mates or territory. 10. Schjelderup-Ebbe first described the dominance hierarchy of chickens from the pecking order that the animals established in a barnyard. 11. Weaker members may die in times of food shortage, etc. as a consequence of this arrangement; this sacrifice results from the individual advantage that stronger, dominant individuals possess. D. Territoriality (Figure 36.17) 1. A territory is a fixed area whose occupants exclude intruders of the same species. 2. Territorial defense occurs in insects, crustaceans, fishes, amphibians, lizards, birds and mammals. 3. Territoriality may be an alternative to dominance behavior. 4. High cost of maintaining the territory boundaries may outweigh the benefits. 5. Most energy may be expended in establishing a territory; once established, it may be easy to defend. 6. Male songbirds establish territories; the population remains stable as young assume the parent’s role. 7. Sea birds may establish a territory in a colony that is barely the size of one nest site. 8. Mammals have home ranges rather than territories, and ranges may overlap. 9. A baboon troop may switch ranges to obtain better resources. E. Mating Systems (Figures 36.18, 36.19) 1. Behavioral ecologists classify mating systems by the extent males and females associate during mating. 2. Monogamy is an association between one male and one female at a time. 3. Polygamy is a term that incorporates all male and female systems with more than one mate. 4. Polygyny indicates that a male mates with more than one female. 5. Polyandry is a system where a female mates with more than one male. 6. Resource defense polygyny occurs when males mate with females by holding critical resources. 7. Female defense polygyny occurs when females aggregate and are defendable. 8. Male dominance polygyny occurs when females select mates from aggregations of males competing for an opportunity to mate, as when a female grouse selects a male on a communal display ground or lek. F. Cooperative Behavior, Altruism, and Kin Selection (Figures 36.20, 36.21) 1. If animals behave selfishly to produce as many offspring as possible, then why do some animals help others at risk to themselves? 2. Some cooperative behavior may be explained easily; some forms of cooperative behaviors seem to require additional explanation. 3. Until the mid-1960s, it was difficult to explain altruistic behaviors. 4. Group-selection theory suggested that animals that helped others “for the good of the species” helped the group survive, and selection was therefore at the group level. 5. Group-selection is not supported by field evidence; there is nothing to prevent a cheater who lacks the genes from benefiting and leaving more offspring (and genes) than the altruistic risk-taker. 6. Mathematical game theory is now used to study behaviors to determine if they are evolutionarily stable strategies or ESSs. An ESS is expected to persist over long periods of evolutionary time. 7. Kin Selection a. In 1964, William Hamilton proposed a theory of kin selection. b. Fitness is not just measured by an animal’s own offspring, but the increase or decrease in genes shared in the gene pool. c. Alleles are shared closely with parents and siblings. d. Inclusive fitness is the relative number of an individual’s alleles that are passed on to future generations from one’s own offspring or that of related individuals. e. This explained the mathematics that allows eusocial insect workers to give up reproduction and aid the queen: in a haplodiploid system, workers are 75% related to their sister queen’s offspring compared to only 50% related to their own offspring if they were fertile and mated. f. This places a high value on being able to recognize kin from non-kin. g. In many haplodiploid insects, reproductive females have multiple mates; therefore, nonreproductive females are not likely tending only their full siblings. 36.5. Animal Communication A. Signals 1. Through communication, one animal can influence the behavior of another. 2. Animals are limited to communication using sounds, scents, touch, pheromones and movement. 3. In contrast to learned and highly variable human language, animal communication is by signals. 4. Each signal conveys one message and cannot be rearranged to construct new kinds of information. 5. The song of a cricket signals the species, sex, location and social status of the sender. 6. The cricket cannot alter his song to provide additional information. B. Chemical Sex Attraction in Moths (Figure 36.22) 1. Virgin female silkworm moths have special scent glands to produce pheromones to attract males. 2. Adult male moths smell with their large antennae covered with thousands of sensory hair receptors. 3. The chemical attractant, bombykol, is detected and the male moth locates her. 4. Such chemical communication evolves easily since there is selection for any improved detectors. C. Language of Honeybees (Figure 36.23) 1. Honeybees can communicate the location of food. 2. The Waggle Dance a. This dance is used when a worker has located a rich source of pollen or nectar. b. The dance is a figure-eight pattern on the vertical surface of a comb inside the hive. c. The waggle run in the middle of the figure eight indicates the direction relative to the sun. d. The tempo of the waggle is inversely related to the food’s distance from the hive. e. When food is plentiful, dancing is less common; if food is scarce, dances are intense. D. Communication by Displays (Figure 36.24) 1. A display is a behavior that serves a communicative purpose. 2. Moth pheromones, bee dances, gull alarm calls and courtship dances are all displays. 3. The elaborate displays of the blue-footed boobies ensure that the message is understood. 4. Redundancy of display behavior also ensures that both partners are committed in courtship. E. Communication Between Humans and Other Animals 1. Humans may have difficulty determining what sensory channel an animal is using. 2. Animal Cognition a. Animal cognition is a general term for mental function, including perception, thinking and memory. b. Recent studies have focused on non-human primates and African grey parrots. c. Researchers taught a chimpanzee to use 132 words in American Sign Language. d. Parrots can vocalize like humans; work with the African gray parrot reveals ability to identify shapes, colors and numbers. e. Studies of animal cognition attempt to detect the extent some animals are capable of self-awareness and various levels of reasoning. Lecture Enrichment 1. This is a field of zoology where care with terminology is very important, and there are far more definitions provided in this chapter than in any other chapter. It is critical to avoid “anthropomorphizing,” using terms that place human thoughts into the minds of animals, for animals do not mentally verbalize. 2. Animal behavior is a fabulously interesting part of zoology, but only if students can see the behaviors that are often rare or seasonal or hard to view in nature. Therefore, use of videos is particularly important in this section to illustrate the often complex behaviors described. 3. Nearly seventy years ago and well before William Hamilton, J.B.S. Haldane [of the Oparin-Haldane hypothesis] wrote a brief and very readable article describing the limited benefits of a gene for altruism. His example is useful in classes to simplify the complex mathematics. If a gene promoted jumping overboard to rescue a person, and the risk of drowning from such an action was 1-in-10, simple genetics allows us to calculate that the gene will increase in frequency if we only save our own children, brothers and sisters (who share one-half of our genes) or our grandchildren and near distant relatives who share one-fourth or one-eighth our genes. Consequently, if we save more distant relatives or strangers, the gene would fade from existence because it now has a higher chance of being lost than saved–the chance of dying exceeds the chance of saving the gene carriers. 4. It is very important not to exaggerate the reports of animal use of language. A critique of such research is available in Joel Wallman’s Aping Language, Cambridge University Press, 1993. 5. Likewise, students may confuse evidence of animal self-recognition to human self-awareness. To distinguish these, an instructor can use examples from D.L. Cheney and R.M. Seyfarth, How Monkeys See the World, Univ. Chicago Press, 1990. Commentary/Lesson Plan Background: Misconceptions: Schedule: HOUR 1 36.1. Science of Animal Behavior A. Ethology 36.2. Describing Behavior: Principles of Classical Ethology A. Early Work 36.3. Control of Behavior A. Innate Behavior B. Genetics of Behavior C. Learning and the Diversity of Behavior 36.4. Social Behavior A. Definitions B. Selective Consequences of Sociality C. Aggression and Dominance D. Territoriality E. Mating Systems F. Altruistic Behavior and Kin Selection 36.5. Animal Communication A. Signals B. Chemical Sex Attraction in Moths C. Language of Honeybees D. Communication by Displays E. Communication between Humans and Other Animals ADVANCED CLASS QUESTIONS: 1. What evidence would you seek to determine if left or right handedness was genetic or learned? With humans, we do not conduct breeding experiments but must work with natural assortments of individuals. If handedness was a Mendelian trait with one handedness dominant and the other recessive, what combinations would disprove a simple hereditary model? Answer: To determine if left or right-handedness is genetic or learned, researchers can gather various types of evidence from studies involving human populations. Here are some approaches and evidence that could be sought: 1. Family Studies: Family studies involve examining handedness patterns within families to assess whether there is a genetic component. If left-handedness tends to run in families more than expected by chance, it suggests a genetic influence. Researchers can compare the handedness of parents with that of their children to look for patterns of inheritance. 2. Twin Studies: Twin studies involve comparing the handedness of monozygotic (identical) twins, who share 100% of their genetic material, with that of dizygotic (fraternal) twins, who share about 50% of their genetic material on average. If monozygotic twins are more likely to share the same handedness compared to dizygotic twins, it suggests a genetic influence. 3. Genetic Studies: Advances in molecular genetics have enabled researchers to identify specific genetic variants associated with handedness. Genome-wide association studies (GWAS) and candidate gene studies can identify genetic markers or genes that are associated with handedness. These studies can provide insights into the genetic basis of handedness. 4. Cross-Cultural Studies: Cross-cultural studies involve examining handedness patterns across different cultures and populations to assess the role of environmental factors. If handedness patterns vary between cultures or change over time within the same culture, it suggests that environmental influences such as cultural practices or educational systems may play a role. 5. Neurobiological Studies: Neurobiological studies involve examining brain structure and function differences between left-handed and right-handed individuals. Differences in brain lateralization or asymmetry may provide clues about the underlying neurobiological mechanisms of handedness. Regarding the question about a Mendelian model of handedness inheritance, if handedness were a simple Mendelian trait with one handedness dominant (let's say right-handedness) and the other recessive (left-handedness), certain combinations of offspring would disprove this model. Specifically, if two right-handed parents consistently produced left-handed offspring, or if two left-handed parents consistently produced right-handed offspring, it would contradict a simple dominant-recessive model of inheritance. These outcomes would suggest that handedness is not determined by a single gene with dominant and recessive alleles but likely involves more complex genetic and environmental factors. 2. In a most general sense, as we move from protozoans to mammals there is an increase in the repertoire of learned behaviors. Why? Answer: The increase in the repertoire of learned behaviors as we move from protozoans to mammals can be attributed to several factors related to the complexity of nervous systems, cognitive abilities, and ecological challenges faced by different organisms: 1. Nervous System Complexity: Protozoans have relatively simple nervous systems consisting of basic neural networks or sensory structures that allow them to detect and respond to environmental stimuli. As we move up the evolutionary ladder to more complex organisms like mammals, the nervous system becomes increasingly elaborate, with specialized regions for processing sensory information, coordinating motor responses, and supporting higher cognitive functions. This increased neural complexity provides the foundation for more sophisticated learning and behavioral flexibility. 2. Cognitive Abilities: Mammals possess advanced cognitive abilities compared to protozoans, including higher-order processing, memory formation, problem-solving, and social learning. These cognitive capabilities enable mammals to learn from past experiences, adapt to changing environments, and exhibit a wide range of complex behaviors such as tool use, communication, and cultural traditions. 3. Ecological Challenges: Mammals inhabit diverse and dynamic environments characterized by complex social interactions, varied food sources, and ever-changing ecological conditions. To navigate and thrive in these environments, mammals have evolved sophisticated learning mechanisms that allow them to acquire new skills, adjust their behaviors, and exploit available resources effectively. Learning enables mammals to respond adaptively to environmental challenges, avoid predators, find mates, secure food, and raise offspring successfully. 4. Social Learning: Many mammalian species engage in social learning, where individuals observe and imitate the behaviors of others within their social group. Social learning facilitates the transmission of knowledge, skills, and cultural traditions across generations, leading to the accumulation of learned behaviors over time. This mechanism allows mammals to benefit from the collective knowledge and experiences of their peers, enhancing their ability to survive and reproduce in complex social environments. 5. Longer Lifespans and Developmental Periods: Mammals generally have longer lifespans and more extended developmental periods compared to protozoans, providing greater opportunities for learning and behavioral refinement over time. Extended periods of parental care and social bonding also contribute to the transmission and acquisition of learned behaviors among mammalian offspring. In summary, the increase in the repertoire of learned behaviors as we move from protozoans to mammals reflects the progressive evolution of nervous system complexity, cognitive abilities, and adaptive strategies that enable organisms to thrive in diverse and challenging environments. PART V ANIMALS AND THEIR ENVIRONMENTS 37 The Biosphere and Animal Distribution 38 Animal Ecology CHAPTER 37 ANIMAL DISTRIBUTIONS CHAPTER OUTLINE 37.1. Earth Environment A. Overview 1. Water has physical properties critical to life on earth. 2. The steady supply of sunlight maintains a suitable range of temperatures for life metabolism. 3. Living matter requires a supply of major and minor elements available on earth. 4. The earth’s gravity is strong enough to hold an extensive gaseous atmosphere. 5. The earth is an open system with a continuous supply of energy. 6. As a consequence of points 4 and 5, life is part of a cycle of life-death-decay-recycling. Building materials for life come from producers and are cycled through consumers. 7. There is a reciprocal relationship between the Earth and the organisms that inhabit it: the Earth is being continually modified by organisms; in turn, how organisms have been modified over time has resulted by various environmental factors. The appearance of free atmospheric oxygen over the Earth’s history exemplifies the reciprocity of life and the Earth. 37.2. Principles of Historical Biogeography A. Geological History 1. Zoogeography studies why animals are distributed where they are and how they disperse. 2. Most animals have a limited geographic range; some, like humans, can live anywhere. 3. Geographic barriers can prevent a population from moving to suitable habitats. 4. The fossil history of an animal species can be important to understand why it is present or not present in its current range; for instance, ancestors of camels originated in North America and moved across Alaska to Eurasia and Africa. Their descendants occur as true camels in Africa and llamas in South America, but are not found in North America nor Alaska. 5. Understanding climatological and geological changes are important to zoogeography. 6. Using phylogenetic systematics, past and current geographic distributions can be used in conjunction with cladograms to hypothesize species’ geologic histories. For example: a. Phylogenetic analysis shows that, except for 2 species in Asia, hellbenders are most closely giant salamanders. b. Molecular calibration of their phylogeny places the split at about 28 million years ago. c. The best hypothesis is that giant salamanders originated in east Asia and a hellbender lineage dispersed to North America. B. Disjunct Distributions (Figure 37.1) 1. Disjunct distributions occur when closely related species live in widely separated areas. 2. There are two possible explanations for disjunct distributions. a. Dispersal is the simple movement of a population from one locale to another and the intervening territory is not suited for long-term colonization. b. A second scenario has a widely distributed population broken into separate populations due to a vicariance event such as climate change, habitat fragmentation or movement of landmasses. C. Distribution by Dispersal 1. Dispersal includes emigration away from a home region and/or immigration into another region. 2. Dispersal is one-way movement, not to be confused with seasonal migrations. 3. Animals can disperse under their own power, or passively disperse by wind, floating, etc. 4. Animals have high reproductive rates; this provides continuous pressure to move into new ranges. 5. The retreat of Pleistocene glaciers left favorable habitats for animals that could disperse into them. 6. In tracing back the origin of animals, as in the case of flightless ratite birds on isolated islands, it is necessary to locate the center of origin of the species. 7. Long-distance dispersal and vicariance events are both used to explain current animal distributions. D. Distribution by Vicariance (Figures 37.2 and 37.3) 1. Fragmentation of biotas by geographic barriers is referred to as vicariance. The study of this phenomenon is called vicariance biogeography. 2. Since speciation is likely to occur when populations are geographically isolated, an analysis of the relatedness of modern species should match up with geographically isolating or vicariant events. 3. One of most dramatic vicariant phenomenon is continental drift (Figure 37.2, Section E below), where over the course of geologic time a once continual terrestrial landmass was sequentially broken into continents and islands that are now separated by ocean. 4. A branching pattern for species that matches the pattern of vicariant events forms a general area cladogram that depicts the history of fragmentation of the geographic areas studied. The remaining branch may be a case of dispersal. a. Example: allopatric evolution of flightless birds (Figure 37.3), where branches within a current cladogram of this group are supported by theoretical vicariant events. E. Continental Drift Theory (Figures 37.2, 37.4) 1. Wegener proposed theory in 1912; ignored until theory of plate tectonics provided a mechanism. 2. The Earth’s surface is composed of 6 to 10 rocky plates that shift on a malleable underlying layer. 3. The Earth’s continents have been drifting since the breakup of a single landmass called Pangaea. 4. Pangaea split 200 million years ago, forming a northern Laurasia and a southern Gondwana. 5. About 135 million years ago, these supercontinents further fragmented and drifted apart. 6. This theory is now supported by the fit of continents, paleomagnetic surveys, seismographic studies, mid-ocean ridges where the ocean bottoms spread, and much biological data. 7. The Case of Marsupial Evolution a. Marsupials appeared about 100 million years ago in South America. b. They spread through Antarctica and Australia that were at that time joined together. c. Marsupials encountered placental mammals in North America and could not compete, and became extinct; the modern opossums are recent arrivals from South America. d. The placental expanded into South America, but the marsupials were well established there. e. About 50 million years ago, Australia drifted apart from Antarctica and remained in isolation with only marsupials to diversify on the continent. F Temporary Land Bridges (Figure 37.5) 1.. Temporary land bridges are important for dispersal; the bridge across the Bering Strait was an important corridor for placentals to enter North America. 2. The land bridge connecting North to South America was absent 50 million - 3 million years ago, but accounts for dramatic changes in animal life after the bridge was reestablished (Figure 37.5). G. Climatic Cycles and Vicariance (Figure 37.6) 1. Withn past 3 million years, 20,000-100,000-year-long cycles of higher or lower average world temperature have occurred. 2. During cold periods, glaciers covered terrestrial areas and sea levels fell; during warm periods, glaciers melted and sea levels rose. 3. Such climate changes have affected geographic distributions of various animals; for example, the current geographic distribution of Appalachian salamanders with respect to latitude, longitude, and altitude (Figure 37.6) can be explained by such cycles. 4. Although climatic cycles can create problems (a.k.a. “deep-history problems”) with the use of general area cladograms in biogeographic studies, it does not diminish the importance of vicariance to biogeography. 37.3. Distribution of Life on Earth (Figures 37.7, 37.8) A. Biosphere and Its Subdivisions 1. The biosphere is the thin outer layer of the earth capable of supporting life. 2. The biosphere is a global system including all life on earth and their physical environments. 3. The lithosphere is the rocky material of the earth’s shell and is the source of all mineral elements. 4. The hydrosphere is the water on the earth’s surface; extends into the lithosphere and atmosphere. a. The global hydrological cycle involves evaporation, precipitation and runoff. b. Five-sixths of global evaporation is from the ocean; more evaporates from ocean than returns; this difference is rainfall that supports life on land. 5. Atmosphere extends 3500 km above the earth surface; life is confined to the lower 8–15 km. a. A layer of oxygen-ozone screens ultraviolet light at between 20 and 25 km altitude. b. Gases present in the atmosphere are nitrogen (N2, 78%), oxygen (O2, 21%), argon (Ar, 0.93%), carbon dioxide (CO2, 0.03%) and varying amounts of water (H2O) vapor. c. Atmospheric oxygen originates nearly completely from photosynthesis. d. The present O2 level was reached by the mid-Paleozoic about 400 billion years ago. e. The earth’s O2 surplus will remain due to its vast supply and ongoing photosynthesis. f. Current rapid input of CO2 from burning fossil fuels may significantly affect the earth. 1) Much of the sun’s energy is absorbed and re-radiated as heat energy. 2) The greenhouse effect describes the measurable trapping of this heat in the atmosphere. 3) Carbon dioxide is a greenhouse gas and adds to this effect. 4) Accumulation of CO2 could lead to an increase in the temperature of the biosphere. B. Global Climate Influences on Animal Environments (Figures 37.9-37.11) 1. Global variation in climate arises from uneven heating of each region due to the solar radiation. a. Global temperature 1) More sunlight/unit area hits the equator; therefore more heat is absorbed (Figure 37.9). 2) Warmed air is lighter and rises and moves toward the poles; it is replaced by cooler air moving along the surface from the poles. 3) The Earth’s rotation on its axis can “bend” air cells in a clockwise or counterclockwise manner. This affect upon air circulation is called the Coreolis Effect. 4) As a consequence of the differential heating of the Earth and the Coreolis Effect, air circulation in each hemisphere is broken into three latitudinal zones or cells (Figure 37.10). b. Global precipitation 1) The same two factors that affect global temperature affect global precipitation. Hot moist air from the equator cools as it rises, condensing and saturating the rain forests; dry air sinks at 20–30o latitude; it sinks in regions where there are subtropical belts of deserts. c. Ocean currents (Figure 37.11) 1) The Coreolis Effect, as well as the sinking of colder, denser water and the rising of warmer, lighter water affects the general movement of ocean currents. 2) Land masses in the way of oceanic currents bend the currents in various diretions. C. Terrestrial Environments: Biomes (Figures 37.12.–37.6) 1. A biome is a major biotic unit with characteristic and easily recognized plant life. 2. Plant distribution is easier to map, but plant formations support characteristic animal life. 3. Biomes are distinctive but the boundaries are not; communities blend into one another. 4. A gradient from forest to woodlands to prairies forms ecoclines of diversity; however, each biome is characterized by dominant plants and animals. 5. Temperate Deciduous Forest a. Temperatures are moderate (relatively not too hot or cold), but are seasonally variable. b. Rain falls throughout the year (climate is relatively wet). c. These forests, dominated by deciduous, broad-leafed trees that are adapted for low-energy levels from the sun and for freezing winter conditions (such as oak, maple) are well developed in eastern North America. d.. In the summer, the closed canopy creates a deep shade underneath; therefore, understory plants grow rapidly in spring or fall. e. Animal communities are adapted to seasonal changes; some migrate and some hibernate. 8. Coniferous Forest (Figure 37.13) a. Mean temperatures colder than temperate deciduous forest (range from 23o-37oF). b. Mean precipitation 80 inches each year. c. High temperatures and rainfall facilitates luxurious, uninterrupted growth that is at a maximum in rain forests. d. Extremely high in biodiversity. Compared to deciduous forests with a few dominant tree species, the tropical forest may have up to a thousand species and none are dominant. d. Tropical forests are often stratified into six to eight feeding strata. e. Insectivorous birds and bats fly the air above the canopy. f. Middle zones have tree species such as monkeys and tree sloths, birds and amphibians. g. Climbing animals range along the trunks. h. Large mammals that are unable to climb forage on the forest floor. i. A large community of carnivores and herbivores scavenges litter and on trunks for food. j. Food webs are intricate and difficult to unravel. k. Litter is thin and the soil is an impoverished laterite; most of biomass is in the forest above. 10. Grassland (Figure 37.15) a. Average annual temperatures range from 50o-68o. b. Average rainfall ranges from a mean of about 31 inches in the east to 16 inches in the west. c. North American prairie is one of the most extensive grasslands in the world. d. Much prairie has been transformed into the most productive agricultural region in the world. e. In grazing lands, nearly all native grasses have been replaced by exotic species. f. The bison was the dominant herbivore, but jackrabbits, antelope, and prairie dogs remain. g. Mammalian predators include coyotes and the now uncommon ferrets and badgers. h. Large areas of tall-grass prairie remain in Kansas and Oklahoma, while large tracts of short-grass prairie can be found in western Kansas and Nebraska. 11. Tundra (Figure 37.16) a. Tundra is a severely cold biome; average temperature is 14oF. b. Soil remains frozen most of the year; annual precipitation is usually 2 species reduce niche overlap to share the same general resources, they form a guild. C. Predators and Parasites (Figures 38.10–38.12) 1. Many animals and plants are in co-evolutionary relationships; each is in a race with the other. 2. If a predator relies primarily on a single prey species, the populations cycle with each other. 3. The time lag between cycles is demonstrated with protozoa and the snowshoe hare and lynx. 4. The predator-prey relationship has led to development of mimicry, where harmless species mimic models that have toxins or stings. 5. Another mimicry complex consists of many different species, all with noxious or toxic factors, that evolve to resemble each other. 6. A keystone species is so critical to a community that its loss causes drastic changes in the community. 7. Keystone species reduce competition and allow more species to coexist on the same resource. 8. Periodic natural disturbances also allow more species to coexist in diverse communities. 9. Ectoparasites not only secure nutrition from their host but are also dispersed by the host. 10. Endoparasites have lost ability to choose habitats and must have tremendous reproductive output to ensure that some offspring will reach another host. 11. Generally, the parasite and host co-evolve toward a less virulent relationship because the death of the host also ends or shortens a parasite’s life; exceptions occur when alternative hosts are available. 38.3. Ecosystems (Figure 38.13) A. Trophic Levels 1. Energy flows through organisms and is used to construct and maintain organisms at several levels. 2. Primary producers, usually green plants, fix and store energy, usually from sunlight. 3. Herbivores are the first level of consumers that eat plants. 4. Carnivores eat herbivores (forming a second level of consumer) or eat carnivores forming higher trophic levels. 5. The most important consumers are decomposers, mainly bacteria and fungi, that break dead organic matter into mineral components at levels for reuse by plants to start the cycle over again. 6. The chemical cycle is endless through the system. 7. However, energy is lost as heat and must constantly be replenished; ecosystems are open systems. B. Energy Flow and Productivity (Figure 38.14) 1. Every organism has an energy budget and must obtain enough energy to grow, reproduce, etc. 2. Gross productivity (Pg) is total energy assimilated or taken in; some is used to maintain metabolism. 3. Net productivity (Pn) is energy stored in the animal’s tissue as biomass; this energy is available for growth of the animal and for reproduction of other individuals. 4. Energy is limited and can be represented as Pn = Pg - R where R is respiration. 5. The energy budget of every animal is finite; growth and reproduction can only occur after metabolism is accomplished. 6. Much energy is lost when it is transferred between trophic levels in food webs. 7. More than 90% of the energy in an animal’s food is lost as heat; less than 10% is stored as biomass. 8. Each succeeding trophic level contains only 10% of the energy of the next lower trophic level. 9. This 90% loss of energy between trophic levels produces ecological pyramids. 10. The Eltonian pyramid is based on numbers of individuals at each trophic level; however, many small insects may feed on one large plant. 11. A pyramid of biomass can be built on the mass of organisms at one point in time. 12. Biomass is usually pyramidal and solves the small insect-large plant dilemma. 13. A biomass pyramid may still be inverted due to food stored in a consumer over time as well as failure to measure the rapid productivity of some producers. 14. Energy pyramids encompassing the lifespan of all organisms involved show a pyramid relationship. C. Life Without the Sun (Tables 38.1, 38.2) 1. From 1977 to 1979, dense communities were first discovered on sea floor thermal vents. 2. The producers in these vent communities are chemoautotrophic bacteria that oxidize hydrogen sulfide. 3. The tubeworms and bivalve molluscs form trophic communities that rely on this non-photosynthetic source of nutrients. D. Nutrient Cycles (Figure 38.15) 1. Decomposers feed on the remains of animals and plants and return substances to the ecosystem. 2. Biogeochemical cycles involve exchanges between living organisms, rocks, air and water. 3. The continuous input of energy from the sun keeps nutrients flowing and the ecosystem functioning. 4. Synthetic compounds challenge nature’s nutrient cycling. 5. Pesticides in food webs can be insidious for three reasons. a. They may be concentrated as they travel up through succeeding trophic levels. b. Many species that are killed by pesticides are not pests. c. Some chemicals have great longevity in the environment. 6. Genetic engineering of crop plants aims to improve resistance to pests and lessen the need for chemical pesticides. 38.4 Extinction and Biodiversity (Figure 38.16) A. Biodiversity 1. Rates of speciation on average slightly exceed rates of extinction. 2. Approximately 99% of all species that have ever lived are extinct. 3. Speciation rates represent an ongoing process of geographic expansion of populations followed by geographic fragmentation. 4. Speciation rates vary greatly among animal taxa. 5. Extinction rates show peaks and valleys through the earth’s history. 6. Estimates of extinction rates as measured in marine fossils average about 25% per million years. 7. Episodocity of extinction can be measured using Raup’s “kill curve.” 8. The “big five” mass extinctions collectively represent only 4% of species extinctions in the past 600 million years. (Table 38.1) 9. Species with large geographic ranges have lower average extinction rates than those with small ranges. 10. A paradox of biodiversity is that habitat fragmentation simultaneously increases rates of both local extinction and speciation. 11. Higher taxa gain some protection from extinction by having large geographic ranges. 12. When higher taxa distributed over a wide area go extinct, it is typically the result of unusually catastrophic conditions. 13. Darwin explained extinctions of higher taxa by interspecific competition, but this claim is refuted by paleontological studies. 14. Fossil studies of extinction allow us to place in perspective the consequences of anthropological impacts on biodiversity. 15. Fragmentation may lead to high rates of speciation, but these young species are particularly prone to extinction because of their small geographic ranges. 16. A major challenge in biodiversity is to obtain an inventory of the earth’s species diversity. 17. Estimates are as high as 10 million species, but this could be low by an order of magnitude. 18. Maintenance of diverse ecosystems is an initial priority for preventing widespread species extinction. 19. Humans must avoid creating conditions that would selectively destroy higher taxa. Lecture Enrichment 1. The mathematics of population growth is a traditional area of difficulty for biology students more accustomed to hands-on organisms than abstract mathematics. Mathematics is also not a regular part of everyday biology lectures and requires a systematic presentation with close association with real examples. Growth curves are a form of “story problem” in math that some students dread; use of concrete examples will defuse some of this anxiety. 2. In enzootic diseases such as bubonic plague, the wild rodents of southeast Asia are more immune to the disease than are rodents in India, and rodents in Europe and the Americas are most susceptible. This provides a way to reconstruct the evolutionary history in that, the longer the parasitic relationship remains stable, the more benign the effect because the more resistant hosts have greater survivorship. 3. It is important not to extend food chain economy to political conclusions not justified by real conditions. The example of eating beef versus eating the grain that could be fed to beef to produce the biomass of meat is a useful teaching example. However, it is not possible to feed pure grain alone to a cow (it would kill it) nor are most cattle fed primarily grain. Indeed, much beef is produced on grasslands that cannot be plowed for grain production. The meat produced in China is virtually all produced on marginal resources, and ending meat consumption there would result in no grain savings and would drop national nutrition levels dramatically. 4. The annual sunlight that strikes the earth and the proportion that enters the food chain via photosynthesis limit the energy budget for the earth. As a result, it is possible to calculate the theoretical maximum of plant tissue, and therefore animal tissue, that the earth can support. As the human population grows, we must “re-budget” this energy consumption from wildlife to us and, contrary to non-science business pronouncements, there is an absolute limit to the amount of life that can be supported on earth. Commentary/Lesson Plan Background: Many ecological terms have definitions distinct from everyday usage; “population” is fairly close to our common usage, but “community” and “competition” and other terms have distinct and often mathematically defined meanings. Rural students may recognize putting up hay as harvesting biomass; any student who has mowed a lawn has likewise harvested biomass, although both cases fail to account for the substantial belowground root biomass. Concepts of energy and mass may be very limited by the limited amount of physics in the U.S. curriculum. Some time may have to be spent reviewing basic physics concepts about energy and the laws of thermodynamics, remembering that these were briefly explained early in this text. Misconceptions: Students may have difficulty imaging the energy in sunlight as related to the energy in chemical bonds in plant and animal tissue; the explanation of the measurement of a calorie in a calorimeter may help students see that this is one continuous phenomenon. The inverted pyramid found in intertidal areas often appears as a contradiction of the loss of energy as we move up the food chain; it is important to work through the values over time to show that they do indeed conform to the laws of physics. Schedule: More time will be needed if illustrations are given of nutrient cycles if time is used to develop the mathematics of the logistic growth curve or energy flow through food webs. HOUR 1 38.1. Hierarchy of Ecology A. Definitions and Levels of Study B. Environment and the Niche C. Populations 38.2. Community Ecology A. Interactions Among Populations in Communities B. Competition and Character Displacement C. Predators and Parasites HOUR 2 38.3. Ecosystems A. Trophic Levels B. Energy Flow and Productivity C. Life Without the Sun D. Nutrient Cycles 38.4 Extinction and Biodiversity ADVANCED CLASS QUESTIONS: 1. Why is a “perfect predator,” that can efficiently hunt and kill any prey it seeks, not found? Answer: The concept of a "perfect predator" that can efficiently hunt and kill any prey it seeks is not found in nature due to several reasons: 1. Ecological Balance: Ecosystems are complex and interconnected, with a delicate balance between predators and prey. If a predator were to efficiently hunt and kill any prey it seeks without constraint, it could lead to destabilization of ecosystems, overexploitation of prey populations, and ultimately collapse of the ecosystem. 2. Co-evolution: Predators and prey species often co-evolve in response to each other's adaptations and behaviors. Prey species develop defenses and adaptations to avoid predation, such as camouflage, warning coloration, defensive structures, or behaviors like hiding or fleeing. Predators, in turn, evolve hunting strategies, physical adaptations, and behaviors to overcome prey defenses. This co-evolutionary arms race prevents any single species from becoming a "perfect predator" that can overcome all prey defenses. 3. Resource Limitations: Predators face constraints on their energy, time, and resources, which limit their ability to hunt and kill prey indiscriminately. Efficient hunting requires energy expenditure, and predators must balance their hunting efforts with other activities such as resting, territorial defense, and reproduction. Additionally, predators must compete with other predators for access to prey resources, further limiting their ability to hunt without constraint. 4. Variability in Prey Populations: Prey populations vary in abundance, distribution, behavior, and vulnerability, making it challenging for predators to consistently locate and capture prey. Some prey species may be rare or elusive, while others may exhibit defensive behaviors or adaptations that make them difficult to hunt. Predators must adapt their hunting strategies and behavior to target different prey species based on availability and vulnerability. 5. Environmental Factors: Environmental factors such as habitat structure, weather conditions, and seasonal changes can influence predator-prey interactions and hunting success. Predators must navigate these environmental factors while hunting, which can affect their ability to efficiently locate and capture prey. Overall, the absence of a "perfect predator" in nature reflects the complexity and dynamics of predator-prey relationships, as well as the ecological constraints and challenges that shape the behavior and interactions of predators in natural ecosystems. 2. Why would predators not all move toward specializing on one species of prey; what are the benefits of retaining some level of generalist feeding? Then why aren’t all predators generalists, able to take any smaller animal as prey; what are the benefits of specialization? Answer: Predators do not all move toward specializing on one species of prey for several reasons, and there are benefits to retaining some level of generalist feeding. Similarly, not all predators are generalists, able to take any smaller animal as prey, because there are benefits to specialization as well. Benefits of Generalist Feeding: 1. Flexibility: Generalist predators are adaptable and can switch between different prey species depending on availability, abundance, and environmental conditions. This flexibility allows them to exploit a wide range of food resources and survive in diverse habitats. 2. Risk Spreading: By feeding on multiple prey species, generalist predators spread their risk of food scarcity or prey depletion. If one prey species becomes scarce or unavailable, generalist predators can switch to alternative prey without experiencing a significant impact on their survival. 3. Energy Efficiency: Generalist feeding can be energetically efficient because it allows predators to maximize their foraging efficiency by targeting the most abundant or easily accessible prey species at any given time. This minimizes the energy expenditure required for successful hunting. Benefits of Specialization: 1. Efficiency: Specialized predators are highly adapted to hunt specific prey species, allowing them to develop specialized hunting strategies, anatomical adaptations, and behavioral traits optimized for capturing and consuming their preferred prey. This specialization increases hunting efficiency and success rates. 2. Reduced Competition: Specialized predators may face less competition from other predators for their preferred prey species, as they have evolved to exploit niche resources that are less accessible or attractive to generalist predators. This reduces competition for food resources and increases the chances of successful hunting. 3. Optimized Resource Use: Specialized predators may be able to extract more energy and nutrients from their preferred prey species compared to generalist predators, as they have evolved physiological adaptations to efficiently digest and utilize specific types of prey. This optimized resource use can improve the predator's overall fitness and reproductive success. In summary, while there are benefits to both generalist feeding and specialization in predators, each strategy has its advantages in different ecological contexts. Generalist predators are flexible and adaptable, allowing them to exploit a wide range of food resources, while specialized predators are efficient and optimized for capturing specific prey species, reducing competition and maximizing resource use. The diversity of predator feeding strategies contributes to the stability and resilience of ecosystems by facilitating efficient energy transfer and maintaining ecological balance. Predators do not all move toward specializing on one species of prey for several reasons, and there are benefits to retaining some level of generalist feeding. Similarly, not all predators are generalists, able to take any smaller animal as prey, because there are benefits to specialization as well. Benefits of Generalist Feeding: 1. Flexibility: Generalist predators are adaptable and can switch between different prey species depending on availability, abundance, and environmental conditions. This flexibility allows them to exploit a wide range of food resources and survive in diverse habitats. 2. Risk Spreading: By feeding on multiple prey species, generalist predators spread their risk of food scarcity or prey depletion. If one prey species becomes scarce or unavailable, generalist predators can switch to alternative prey without experiencing a significant impact on their survival. 3. Energy Efficiency: Generalist feeding can be energetically efficient because it allows predators to maximize their foraging efficiency by targeting the most abundant or easily accessible prey species at any given time. This minimizes the energy expenditure required for successful hunting. Benefits of Specialization: 1. Efficiency: Specialized predators are highly adapted to hunt specific prey species, allowing them to develop specialized hunting strategies, anatomical adaptations, and behavioral traits optimized for capturing and consuming their preferred prey. This specialization increases hunting efficiency and success rates. 2. Reduced Competition: Specialized predators may face less competition from other predators for their preferred prey species, as they have evolved to exploit niche resources that are less accessible or attractive to generalist predators. This reduces competition for food resources and increases the chances of successful hunting. 3. Optimized Resource Use: Specialized predators may be able to extract more energy and nutrients from their preferred prey species compared to generalist predators, as they have evolved physiological adaptations to efficiently digest and utilize specific types of prey. This optimized resource use can improve the predator's overall fitness and reproductive success. In summary, while there are benefits to both generalist feeding and specialization in predators, each strategy has its advantages in different ecological contexts. Generalist predators are flexible and adaptable, allowing them to exploit a wide range of food resources, while specialized predators are efficient and optimized for capturing specific prey species, reducing competition and maximizing resource use. The diversity of predator feeding strategies contributes to the stability and resilience of ecosystems by facilitating efficient energy transfer and maintaining ecological balance. 3. Why would a mimicry complex, where a harmless species evolves to resemble a noxious species, have limitations on the size of the mimic population? In a mimicry complex where both species are noxious, would there be a limitation on the size of the mimic population? Answer: A mimicry complex, where a harmless species evolves to resemble a noxious species, may have limitations on the size of the mimic population due to several factors: 1. Prey Availability: The size of the mimic population may be limited by the availability of prey that the mimic species resembles. If the population size of the noxious species, which serves as the model for mimicry, is limited by factors such as habitat availability, prey abundance, or environmental conditions, then the mimic population may also be constrained by the availability of suitable prey. 2. Predation Pressure: Mimicry complexes often involve predators learning to avoid noxious or harmful prey based on visual cues. However, if the mimic population becomes too large relative to the population of the noxious species, predators may become more adept at distinguishing between mimics and true noxious species, reducing the effectiveness of mimicry as a protective mechanism. This increased predation pressure could limit the size of the mimic population. 3. Resource Competition: Mimic species may compete with the noxious species for resources such as food, habitat, or mates. If resources are limited, competition between mimics and the noxious species could constrain the size of the mimic population, as individuals may struggle to obtain sufficient resources for survival and reproduction. In a mimicry complex where both species are noxious, there may still be limitations on the size of the mimic population, but these limitations may be less pronounced: 1. Predator Avoidance: If both species in the mimicry complex are noxious and predators learn to avoid both models and mimics based on their shared visual signals, then the mimic population may benefit from reduced predation pressure compared to a situation where only one species is noxious. This could allow the mimic population to achieve larger population sizes without suffering increased predation rates. 2. Resource Partitioning: In some cases, noxious species within a mimicry complex may exhibit different ecological preferences or occupy different niches, allowing them to coexist without direct competition for resources. Mimics may exploit similar ecological niches to the noxious species without directly competing for resources, which could allow for larger mimic populations. While there may still be some limitations on the size of the mimic population in a complex where both species are noxious, these limitations may be mitigated by reduced predation pressure and resource partitioning compared to a situation where only one species is noxious. 4. In a small district in Africa, we might find that the biomass of elephants exceeded the biomass of the plants they ate over a short period of time, forming an “inverted pyramid.” Explain why this is not a contradiction of the second law of thermodynamics. Answer: The concept of the biomass of elephants exceeding the biomass of the plants they eat over a short period of time, forming an "inverted pyramid," is not a contradiction of the second law of thermodynamics because it does not violate the fundamental principles of energy flow or conservation. The second law of thermodynamics states that in any energy transfer or transformation, some energy is lost as heat, resulting in a decrease in the overall availability of usable energy in a closed system. However, this law does not prohibit the temporary accumulation of biomass in specific trophic levels within an ecosystem. In the case of the inverted biomass pyramid observed in the small district in Africa with elephants, several factors could contribute to this phenomenon without violating the second law of thermodynamics: 1. Temporal Dynamics: Ecosystems are dynamic and constantly changing over time. Short-term fluctuations in biomass distribution, such as an increase in the elephant population relative to plant biomass, can occur due to factors such as reproduction rates, migration patterns, or disturbances like droughts or fires. These fluctuations are part of natural ecological processes and do not violate thermodynamic principles. 2. Energy Conversion Efficiency: While energy is lost as heat in each trophic transfer, the efficiency of energy conversion varies between trophic levels. For example, primary producers (plants) typically have a higher energy conversion efficiency than herbivores (elephants) due to factors such as photosynthesis efficiency and metabolic rates. However, under certain conditions, such as rapid plant growth or limited herbivore predation, plant biomass may temporarily exceed herbivore biomass. 3. Biogeochemical Cycling: Nutrient cycling processes, such as decomposition and nutrient recycling, play a crucial role in maintaining ecosystem balance and productivity. Nutrients released during decomposition contribute to plant growth, supporting primary production and biomass accumulation. However, the cycling of nutrients does not violate thermodynamic principles, as the total energy content of the system remains constant. In summary, the observed phenomenon of an inverted biomass pyramid, where the biomass of elephants exceeds the biomass of the plants they eat over a short period of time, is a result of dynamic ecological processes and does not contradict the second law of thermodynamics. Ecosystem dynamics involve complex interactions between biotic and abiotic factors, leading to variations in biomass distribution that are consistent with thermodynamic principles.
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