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Behavioral Ecology. Chapter 8 Behavioral Ecology. CONCEPT 8.1 An evolutionary approach to the study of behavior leads to testable predictions. CONCEPT 8.2 Animals make behavioral choices that enhance their energy gain and reduce their risk of becoming prey
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Chapter 8 Behavioral Ecology CONCEPT 8.1 An evolutionary approach to the study of behavior leads to testable predictions. CONCEPT 8.2 Animals make behavioral choices that enhance their energy gain and reduce their risk of becoming prey CONCEPT 8.3 Mating behaviors reflect the costs and benefits of parental investment and mate defense. CONCEPT 8.4 There are advantages and disadvantages to living in groups.
Baby Killers: A Case Study Lions are the only cats that live in social groups called prides. Adult females in a pride are closely related. A pride hunts cooperatively, and females often feed and care for each other’s cubs.
Baby Killers: A Case Study Adult male lions often kill the cubs of another male in the pride. Why would this behavior be adaptive?
Baby Killers: A Case Study Young adult male lions are driven from the pride and may form “bachelor prides” that hunt together. At 4 or 5 years, a male can challenge adult males in an established pride. If successful, the new male may kill cubs recently sired by the vanquished male.
Baby Killers: A Case Study 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.
Baby Killers: A Case Study Many seemingly odd behaviors exist in the animal world. In many species, females are more “choosy” than males in selecting a mate; but in some species males are choosy, and females try to mate with as many males as possible.
Introduction An animal’s behavioral decisions play a critical role in activities such as obtaining food, finding mates, avoiding predators. These decisions have costs and benefits that affect an individual’s ability to survive and reproduce.
Introduction Behavioral ecology is the study of the ecological and evolutionary basis of animal behavior.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions Concept 8.1 An evolutionary approach to the study of behavior leads to testable predictions.
Concept 8.1An Evolutionary Approach to Behavior Animal behaviors can be explained at different levels: Proximate causes (immediate)—or how the behavior occurs. Ultimate causes—why the behavior occurs; the evolutionary and historical reasons. Behavioral ecologists mostly focus on ultimate causes.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions Because an individual’s ability to survive and reproduce depends in part on its behavior, natural selection should favor individuals whose behaviors make them efficient at foraging, obtaining mates, and avoiding predators. Animal behaviors are often consistent with this prediction.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions 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.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions 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.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions Most aspects of animal behavior are controlled by both genes and environmental conditions. Weber et al. (2013) studied burrow construction in two mice species.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions Oldfield mice build a long entrance tunnel and an escape tunnel, possibly an adaptation to living in open habitats that provide little protective cover. Deer mice construct a simpler burrow, with a short entrance tunnel and no escape tunnel.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions The two mice species can interbreed and produce fertile offspring. All of the F1 hybrid offspring built burrows with escape tunnels, as did about 50% of backcross mice (F1 hybrids mated with deer mice). This indicates that building escape tunnels is controlled by one genetic locus.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions Genetic mapping (quantitative trait locus analysis, or QTL) also showed that entrance tunnel length was controlled by three genetic loci. Although few studies have identified the genes, many behaviors are known to be heritable, and most are influenced by multiple genes.
Concept 8.1 An Evolutionary Approach to the Study of Behavior Leads to Testable Predictions Individuals with an allele for a certain behavior may not always perform that behavior, and may change behavior when in different environments. But by assuming that genes affect behaviors, and natural selection has molded them over time, we can make specific predictions about how animals will behave.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Concept 8.2 Animals make behavioral choices that enhance their energy gain and reduce their risk of becoming prey.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Food availability can vary greatly over time and space. If energy is in short supply, animals should invest in obtaining the highest-quality food that is the shortest distance away.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Optimal foraging theory: Animals will maximize the amount of energy gained per unit of feeding time, and minimize the risks involved. The theory assumes that natural selection acts on the foraging behavior of animals to maximize their energy gain.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Profitability of a food item (P) depends on how much energy (E) the animal gets from the food relative to amount of time (t) it spends obtaining the food:
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey An animal’s success in acquiring food increases with the effort it invests; but at some point, more effort results in no more benefit, and the net energy obtained begins to decrease.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Tests of the model: Benefits may incorporate net energy gained, time spent feeding, or risk of predation. If optimal foraging is an adaptation to limited food supplies, then we must be able to relate the benefit to survival and reproduction of the animal.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey In a study of great tits, proportions of prey types and encounter rates were varied. The time it took birds to subdue and consume the prey (handling time) was measured. The model correctly predicted consumption rates of large mealworms as profitability of prey items varied.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey A field study of Eurasian oystercatchers (Meire and Ervynck 1986) showed that the birds select prey items in a specific size range. Small bivalves do not provide enough energy to offset the energy needed to find and open them. Largest bivalves are too difficult to open.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Marginal value theorem (Charnov 1976): An animal should stay in a 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.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey 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. A “forest” of wooden dowels contained food “patches” of plastic cups containing mealworms.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey “Travel time” was manipulated by covering food cups, and adjusting ease of mealworm removal. Results matched predictions made by the theorem very well.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Optimal foraging theory does not apply as well to animals that feed on 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.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey For foragers, risk of exposure to their own predators is also important. Trade-offs that affect foraging decisions may be related to predators, environmental conditions, or physiological conditions.
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey 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 Elk Change Where They Feed in Response to Wolves
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey 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).
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey 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).
Figure 8.12 Young Receive Less Food When Parents Fear Predators
Concept 8.2 Animals Make Behavioral Choices That Enhance their Energy Gain and Reduce their Risk of Becoming Prey Prey species have evolved a broad range of defenses against their predators. Antipredator behaviors include those that help prey avoid being seen, detect predators, prevent attack, or escape once attacked.
Concept 8.3 Mating behaviors reflect the costs and benefits of parental investment and mate defense Concept 8.3 Mating behaviors reflect the costs and benefits of parental investment and mate defense.
Concept 8.3 Mating behaviors reflect the costs and benefits of parental investment and mate defense Males and females often differ in physical appearance; males often posses 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.
