L06_behavior.pdf

Principles in Ecology PCB 4043 Behavior Prof. Fahimipour Topics: Getting food, living in groups [email protected] D: 437 DW | B: 206 Sanson  Focus on these key concepts… Evolution is the basis for adaptive behavior. Animals make behavioral choices that enhance their ener...

Principles in Ecology PCB 4043 Behavior Prof. Fahimipour Topics: Getting food, living in groups [email protected] D: 437 DW | B: 206 Sanson  Focus on these key concepts… Evolution is the basis for adaptive behavior. Animals make behavioral choices that enhance their energy gain and reduce their risk of becoming prey. Mating behaviors reflect the costs and benefits of parental investment and mate defense. There are advantages and disadvantages to living in groups.  Infanticide in Lion Packs Lions live in social groups called prides, which hunt cooperatively. Females in a pride are closely related and often feed and care for each other’s cubs. Young adult males are driven from the pride and may form “bachelor prides” that hunt together. At 4–5 years, a male can challenge adult males in an established pride.  Infanticide in Lion Packs If successful, the new male may kill cubs recently sired by the vanquished male. A female lion will become sexually receptive soon after her cubs are killed, as opposed to 2 years if she has cubs. The new male is increasing the chances that he will sire cubs before he is replaced by another, younger male.  Infanticide in Lion Packs Many seemingly odd behaviors exist in the animal world. – Fruit flies sometimes lay eggs in food sources that contain high concentrations of ethyl alcohol, a toxic substance – In many species, females are more “choosy” than males in selecting a mate; but in some species the males are choosy, and females try to mate with as many males as possible. Red phalarope (Phalaropus fulicarius)  Introduction An animal’s behavioral decisions play a critical role in obtaining food, finding mates, avoiding predators. These decisions have costs and benefits that affect an individual’s ability to survive and reproduce. Behavioral ecology and ethology are the fields that study the ecological, evolutionary, and neurophysiological basis of animal behavior.  An Evolutionary Approach to Behavior Researchers seek to explain animal behaviors using a variety of approaches. Proximate causes (immediate)—or how the behavior occurs. Ultimate causes—why the behavior occurs; the evolutionary and historical reasons.  An Evolutionary Approach to Behavior Natural selection should favor individuals whose behaviors make them efficient at foraging, getting mates, and avoiding predators. If the traits that confer advantage are heritable, natural selection can result in adaptive evolution: – Traits that confer survival or reproductive advantages tend to increase in frequency over time. Environmental conditions also affect most behaviors, even those that are strongly influenced by genes.  An Evolutionary Approach to Behavior Many studies have documented adaptive behavioral change. – Silverman and Bieman (1993) showed that cockroaches exposed to traps with a bait containing an insecticide plus glucose evolved glucose aversion, which is controlled by a single gene. – Feeding index ranges from 1.0 (indicating that 100% of their diet consisted of agar containing glucose) to –1.0 (indicating that 100% of their diet consisted of plain agar). Error bars show one standard error.  An Evolutionary Approach to Behavior Individuals with an allele for a certain behavior may not always perform that behavior. Two individuals with identical alleles may behave differently. Individuals may change behavior in different environments. By assuming genes affect behaviors, and natural selection has molded them over time, we can make specific predictions about how animals will behave. Most behaviors involve more complex genetic or neurophysiological factors.  Foraging Behavior Food availability varies greatly over time and space, and some food items may be easier to get than others. Optimal foraging theory: Animals will maximize the amount of energy acquired per unit of feeding time. – If energy is in short supply and impacts an animal’s fitness, then selection should act on foraging behavior to increase efficiency. Optimal foraging theory uses mathematical models to evaluate hypotheses associated with adaptive behavior. Robert MacArthur, optimal foraging  Foraging Behavior Optimal foraging can be represented by Enet = E gross /(h + s ) Enet: net energy obtained from a food source Egross: total energy from a food source h: time spent handling the food source s: time spent searching for the food  Foraging Behavior As an animal increases foraging effort, amount of energy obtained increases rapidly at first. But at some point, more effort results in no more benefit, and net energy obtained begins to decrease. If foraging behavior is an adaptation to limited food supplies, then we must be able to relate the benefit of the behavior to survival and reproduction of the animal. Figure 8.6 Conceptual Model of Optimal Foraging  Foraging Behavior Optimal foraging models can be tested in field and laboratory studies. Using an optimal diet selection model in a study of great tits, prey size and handling time was varied (Krebs et al. 1977). – The birds consumed an increasing percentage of large mealworms as the relative profitability of those larger prey increased, as the model predicted. Figure 8.7 Effect of Profitability on Food Selection  Foraging Behavior Marginal value theorem (Charnov 1976): Considers habitat as a heterogeneous landscape made up of patches containing different amounts of food. An animal should stay in a profitable patch until the rate of energy gain has declined to match the average rate for the whole habitat (giving up time). Giving up time is also influenced by distance between patches.  Foraging Behavior A prediction of the marginal value theorem: The longer the travel time between food patches, the longer an animal should spend in a patch. – Cowie (1977) tested this in lab experiments with great tits. Travel time between food patches was manipulated by covering some food cups. – Results matched predictions made by the theorem very well. Figure 8.8 Effect of Travel Time between Patches  Foraging Behavior Optimal foraging theory does not apply as well to animals that eat mobile prey. The assumption that energy is in short supply, and that this dictates foraging behavior, may not always hold. Resources other than energy can be important, such as nitrogen or sodium content of food. For foragers, risk of exposure to predators is also important.  Foraging Behavior Predators can affect foraging decisions. – Presence of wolves affected foraging behavior of elk in the Yellowstone ecosystem (Creel et al. 2005). – Radio collars were used to track elk movements. – When wolves were present, elk moved into forests that had more protection but less food. Figure 8.10 Movement Responses of Male and Female Elk  Foraging Behavior We have examples of similar stuff in aquatic environments. – Small bluegill sunfish were found to spend more time foraging in vegetation if a predator was present, which provided only one-third the food of more open habitats. – Larger sunfish (too large to be eaten by the bass) foraged in ways predicted by optimal foraging theory (Werner et al. 1983).  Foraging Behavior Even a perceived risk of predation can alter foraging patterns. – Song sparrows exposed to recordings of predators fed their young fewer times per hour than did sparrows that heard recordings of nonpredators (Zanette et al. 2011).  Foraging Behavior Prey species have evolved a range of defenses against their predators. Antipredator behaviors include making themselves less visible, ways to detect predators, prevent attack, or escape once attacked. Prey may perform risky activities (such as foraging) during times of day when predators are not active. Figure 8.12 Examples of Antipredator Behaviors  Mating Behavior Males and females often differ in physical appearance; males often possess weapons such as horns, or gaudy ornaments. The sexes may also differ in behavior. Many males fight, sing loudly, or perform strange antics to gain access to females. Figure 8.14 A Male Courtship Dance  Mating Behavior Darwin proposed that the extravagant features of some males resulted from sexual selection: – Individuals with certain characteristics gain an advantage over others of the same sex solely with respect to mating success. – Males with the largest size, strength, and weaponry typically win battles for females and therefore sire more offspring. Example: Bighorn sheep – Extravagant traits, such as brilliant plumage, used by males to lure females could have arisen by sexual selection. Figure 8.15 Males with Long Tails Get the Most Mates – Andersson (1982) showed males with long tails had higher fitness – What are the controls here?  Mating Behavior In some species, males provide females with a direct benefit for mating—nuptial gifts of food, help in rearing young, access to a territory with good nesting sites, food. etc. In some spiders and mantids, males are consumed by the females after mating. – Females are less likely to mate again, increasing the chances that the suicidal males pass on their genes. – Chance of the male finding another mate is low, so the evolutionary cost of suicide for successful mating is low. Figure 8.16 The ultimate gift for copulation  Mating Behavior In some cases, few or no direct benefits are provided to choosy females, but they may receive indirect genetic benefits. Her choosiness may enhance the probability that her sons will mate due to an associated trait that confers higher fitness. – Variation in throat and belly color of the European green lizard was associated with the degree of infection by blood parasites. – Females chose males with brighter coloration, indicating a low degree of infection and therefore more benefit to her offspring. Figure 8.17 Skin Color Brightness Indicates Blood Parasites ­ ­  Living in Groups Some animal species live in groups, e.g., herds of horses, schools of fish, etc. Benefits of group living: – Higher reproductive success—especially when males hold high-quality territories. – Group members may share feeding and care of young. – Reduced risk of predation—individuals can band together to prevent attacks; predators may be detected sooner. Figure 8.19 A Formidable Defense Figure 8.20 Safety in Numbers  Living in Groups Dilution effect: As the number of individuals in a group increases, the chance of being the one attacked by a predator decreases. – Group members may respond to a predator by scattering in different directions, making it difficult for the predator to select a target. Group members may have better foraging success than individuals. – Lions, killer whales, wolves, and others coordinate attacks: actions of one predator drive prey into the waiting jaws of another. – Herbivores in groups may increase the probability of finding good patches of food.  Living in Groups Costs of group living: – As group size (i.e., number of individuals) increases, available food is depleted faster. – More time may be spent in moving between feeding sites. – Competition for food can be more intense. – In groups with a dominance hierarchy, subordinate members can spend much time and energy on interacting with group members. – Group members may live close together or come into contact more often; parasites and diseases can spread more easily.  Living in Groups Quantifying costs and benefits to a group is difficult but we could predict that optimal group size would be the size at which net benefits exceed costs. If other individuals join once optimal size is reached, observed group size may be larger than the optimal. It may be advantageous for individuals to belong to groups that are larger than optimal, but not so large that a new arrival would do better on its own. Figure 8.22 Should a New Arrival Join the Group?  Exam tips Opens on Canvas Wednesday at 9:30AM, closes at 12:00PM. 80 minutes to complete the exam alone (exceptions: accommodation letter). Questions lock after answering. You cannot save ?s for later. Open book, notes, slides are permitted. Working together, ChatGPT are prohibited. Don’t cheat please. It won’t go well. Fair-game material: – Lecture slides and materials – Book chs. 1, 3, 5, 6, 8 – Data figures and experiments we discussed (!) – Readings: Yeakel, West, Couzin (highlighted sections) Remember, best 4 of 5 exams count Format: 1st question is short response, 32 multiple choice