BIOL214 Post Exam - Behavioral Ecology (Lec 25+26)

Behavioral Ecology

• the observable response of organisms to external and internal stimuli

Proximate Causes of Behavior

focus on genetic and physiological mechanisms

Ultimate Causes of Behavior

focus on its effects on reproductive success

Altruism

• behavior that benefits others at personal cost

• some individuals forego reproducing to benefit the group

• most altruistic acts serve to benefit the individual’s close relatives

Reciprocal Altruism Definition

evolution of altruism among nonkin

Group Selection

• the first attempt to explain the existence of altruism (Edwards, 1962)

• natural selection produces outcomes beneficial for the whole group/species

• a group consisting of selfish individuals would overexploit resources and die out, while the fitness of a group with altruists would be enhanced

Individual Selection

• counter argument to group selection made by George Williams

• proposes that particular traits are selected for because they benefit the survival and reproduction of the individual rather than the group

• 3 arguments

  • mutation, immigration, and the lack of an ability to predict future source availability tend to prevent group selection

Argument #1: Mutation

• in a population where individuals limit their resource use, mutant individuals that readily use resources for themselves or their offspring will have an advantage

  • ex. birds with a clutch size of two

    • two eggs ensures replacement of the parent birds but prevents a population explosion

    • if a bird lays three eggs, sufficient food may be available for all three young to survive

    • 3-egg genotype will eventually become more common than the 2-egg genotype

    • brood size could continue to increase until the parents can no longer provide for all their young

Argument #2: Immigration

• selfish individuals that lay more eggs could immigrate from other areas

• populations are rarely sufficiently isolated to prevent immigration of selfish individuals from other populations

Argument #3: Resource Predication

• group selection assumes that individuals can assess and predict future food availability and population density within their own habitat

Infanticide

• population size is more often controlled by competition in which individuals strive to command as much of a resource as they can

  • rather than cooperation

• can result in infanticide

Altruism with Relatives

• William D. Hamilton (1964)

• coefficient of relatedness is associated with the evolution of altruism

• not only does an organism pass on its genes through having offspring, but it can pass them on through ensuring survival of relatives

• an organism has a vested interest in protecting its brothers and sisters and even their offspring

Hamilton’s Rule

• Hamilton proposed that an altruistic gene will be favored by natural selection when:

  • rB > C

  • r - coefficient of relatedness of the donor (the altruist) to the recipient

  • B - benefit received by the recipient of altruism

  • C - the cost incurred by the donor

Inclusive Fitness

• used to designate the total number of copies of genes passed on through one’s relatives, as well as one’s own reproductive output

Kin Selection

• used to designate the behavior that lowers an individual’s own fitness but enhances the reproductive success of a relative

Eusociality

• organisms that have reproductive division of labor, overlapping generations, and cooperative care of young

Eusociality in Ants

• vast majority of females (worker ants) rarely reproduce, but instead help one reproductive female (the queen) raise offspring

• males develop from the queen’s unfertilized eggs and are haploid (their sperm are genetically identical)

• each daughter receives an identical set of genes from her father; the other half of a female’s genes come from her diploid mother

• coefficient of relatedness r of sisters is 0.50 (from father) + 0.25 (from mother) = 0.75

  • haplodiploidy

• females are more related to their sisters (0.75) than their own offspring

  • more advantageous for females to stay in the nest and care for other female offspring of the queen (their full sisters)

Eusociality Continued

• Richard Alexander suggested it was the lifestyle that promotes eusociality in animals instead of genetics

• suggested eusocial species exist when the following conditions are met:

  • individuals are confined to burrows/nests and escape is difficult

  • a dominant individual can prevent other individuals from reproducing

  • food is abundant enough to support high concentrations of individuals

• these conditions are met in naked mole rat colonies

  • females do not reproduce and only the queen has offspring

Reciprocal Altruism

• occurs when the cost to the animal of behaving altruistically is offset by the likelihood of a return benefit

• ex. female vampire bats

  • will regurgitate food to an unrelated female if needed, because at other times, she may be the recipient of such food

  • the recipient delays starvation by about 18 hours whereas the donor accelerates time toward starvation by 6

Prisoner’s Dilemma

Evolutionary Stable Strategy

• a strategy, if which, adopted by a population of players in a given environment, cannot be invaded by any alternative strategy that is initially rare

Group Living

• has advantages and disadvantages

• benefits include group defense against predators (increased vigilance) and protection in numbers

• ex. pigeons

  • if each pigeon occasionally looks up to scan for a hawk, then the bigger the group, the more likely one bird will spot the hawk early enough for the flock to take flight

  • many eyes hypothesis

Scan Frequency

• scan frequency declines with increasing group size

Group Living and Food

• group living allows predators to take down prey of a disproportionately larger size than a single predator would be able to

• when animals search for food in groups, they are able to exploit the discovery of others

  • may result in higher encounter with food items than searching individuals

Orca Group Hunting

• highest payoff is a group size of 3 (optimal group size)

• solitary individuals would benefit from joining the group until 5 individuals

• in a group size of 6, an individual would be better off on its own

• stable group size is 5

Selfish Herd

• William Hamilton

• within a group, each individual can minimize the danger to itself by choosing the location that is as close to the center of the group as possible

• predators are likely to attack prey on the periphery

• when animals are under attack they tend to bunch close together which makes it physically difficult for the predator to get to the center

Foraging Behavior

• food gathering, or foraging, often involves decisions about whether to remain at a resource patch and look for more food or look for a completely new patch

  • the analysis of these decisions is often performed in terms of optimality modeling

• optimality modeling predicts that an animal should behave in a way that maximizes the benefits of a behavior minus its cost

  • the benefits are nutritional or caloric value of the food items and the costs are the energetic or caloric costs of movement

An Organism is Optimizing its Foraging Behavior When…

the difference between the energetic benefits of food consumption and energetic costs of food gathering is maximized

Optimal Foraging Theory

• maximize the benefits and minimize the costs of food gathering

• optimal foraging proposes that in a given circumstance, an animal seeks to maximize the rate of energy gain

• proposes natural selection favors animals that are maximally efficient at propagating their reproductive success and at performing all other functions that serve this function

• the more net energy an individual gains in a limited time → the greater the reproductive success

Northwestern Crow Optimal Foraging

• crows take only large whelks and always drop them from a height of 5m to break them on rocks

• this is because this size whelk dropped from this height needs the fewest drops to break it open

Atta cephalotes Optimal Foraging

• these leaf cutting ants are larger individuals

• however, larger individuals are restricted to foraging at night because of the activity of parasitic flies during the day

• during the day, only small ants forage as these are not subject to the same levels of parasitism

North Atlantic Oscillation

• climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high

• controls the strength and direction of westerly winds and storm tracks across the North Atlantic

  • it is part of the arctic oscillation, and varies over time

North Atlantic Oscillation Effects on Wolves, Moose, and Trees

• heavier snowfall → larger wolf packs

• larger wolf packs kill more moose

• larger wolf packs reduce moose density

• smaller moose density permits greater fir growth

Defending Territories

• a territory is a fixed area in which an individual or group excludes other members of its own species, and sometimes other species, by aggressive behavior or territory marking

• territory owners tend to optimize territory size according to the costs and benefits involved

  • primary benefit of a territory is that it provides exclusive access to a particular resource

Foraging Behavior

• large territories may provide more of a resource but cost more to defend

• small territories that are less costly to defend may not provide enough of a resource

• territory size differs considerably among species

• optimality modeling predicts territory size should evolve to maximize the difference between energetic benefits and costs, thus maximizing the profit to the territory holder

• territories set up solely to defend areas for mating or nesting are often relatively small

Game Theory

• the study of mathematical models of conflict and cooperation between intelligent rational decision-makers (Myerson 1991)

• John Maynard Smith (1976, 1982) investigated fighting behavior in animals by considering contests in which there were different sorts of strategies, modifying the Prisoner’s Dilemma game

  • asking if its better to attack or submit to the attacker

Bourgeois

• hawk if a territory owner

• dove if not a territory owner

• hawk average reward = 12.5

• dove average reward = 7.5

• Bourgeois reward = 25

Game Theory Consequences

1. fighting strategy is frequency dependent

2. the ESS is often a mixture of different strategy types like Hawk, Dove, and Bourgeois

3. the frequency of Hawk behavior increases as the payoff increases

Mating Systems

• Fisher’s Principle states that a 1:1 sex ratio is an ESS as the fitness of one gender is reduced when there is an overproduction of that gender

Promiscuous Mating Systems

• each male or female may mate with many partners

• ex. chimpanzees and bonobos

  • each male mates with many females and vice versa

• ex. intertidal and terrestrial mollusks

• the risk of not finding a mate is believed to promote promiscuity

Mate-Guarding Hypothesis

• theorizes that males stay with a female to protect her from being fertilized by other males

• ex. Dunnocks

Male Assistance Hypothesis

• maintains that males remain with females to help them rear their offspring

• 70% of bird species

Female Enforced Monogamy

• suggests that females stop their male partners from being polygynous

Purple Martin EPC

• older males mate with the females of less experienced males

  • the young fathers only fertilized 1.3 eggs out of clutch of 4.5 eggs

  • the older males father 4.5 fertilized eggs with their mates, plus another 3.6 fertilized eggs with the mates of less experienced males

Mating Systems and Ecology

• species living in stable environments with uniform food distribution tend to be territorial and monogamous

  • ex. dark-backed weaver

• species living in areas that occasionally have superabundant food tend to be polygynous

  • ex. red bishop

• birds that produce precocial young are more likely to be polygynous

Resource-Based Polygyny

• male lark buntings hold territories in shade

• females need shaded nests to promote chick survival

Harem Mating Structures

• more common when females congregate in groups or herds

  • ex. elephant seals

Communal Courting

• where males display in designated communal courting areas

  • ex. sand grouse

Polyandry

• ex. honeybees

  • the queen often mates with multiple males

• ex. spotted sandpiper

  • the productivity of their breeding grounds is so high, the female can lay five clutches of 20 eggs in 40 days

  • reproductive success is not limited by food but by the number of males she can find to incubate the eggs

  • females compete for males, defending territories where the males sit

• females compete for social rank by fighting

Sexual Selection

• selection that promotes traits that will increase an organism’s mating success and can take two forms:

• 1. intrasexual selection

• 2. intersexual selection

Intersexual Selection

• members of one sex choose mates based on particular characteristics

• ex. color of plumage or courtship song

• usually females

Intrasexual Selection

• members of one sex compete over partners

• winner performs most of matings

• usually males

New Caledonian Crows

• research suggests that New Caledonian crows have capacity for abstract thought

  • can use one tool to access another tool that will help them reach food

• discovered by Dr. Alex Taylor

Behavior Evolves

• a behavior is an internally generated response to an external stimulus

• can evolve through natural selection because it can influence the fitness of individuals

  • can vary from individual to individual and the variation is at least partly genetic

• Dmitry Belyaev (1917-1985)

  • demonstrated that docility could be selected for in foxes, resulting in individuals that were reportedly as tame as dogs

Genes Influence Behavior in Foxes

• behavior appeared to be heritable

• Kukekova used QTL to begin identifying genes associated with aggressiveness and Nelson et al. suggested that neural crest cells were particularly important

Derived Freshwater Sticklebacks

• differ in behavior from marine ancestors

• juvenile sticklebacks from freshwater lakes were less social, more aggressive, less likely to school

Oldfield Mice

• most Peromyscus dig only one short tunnel to their nest

• oldfield mice dig elaborate shelters with a long tunnel to the surface and a second tunnel that goes the opposite way

• 3 loci having strong additive effects on escape tunnel length

Behavioral Ecology

• the science that explores the relationship between behavior, ecology, and evolution to elucidate the adaptive significance of animal actions

Proximate Causation

• explains biological function in terms of immediate physiological or environmental factors

Ultimate Causation

• explains traits in terms of evolutionary forces acting on them

Dictyostelium discoides

• to cope with starvation, the cells join to form a slug, which produces spores (but die in the process)

Animals use Neurons to Control Behavior

• spikes of voltage travel down the length of a neurotransmitters at synapse, triggering activity in neighboring neurons

Animal Nervous System Evolution

• evolved through co-opting of genes with other functions

• agreement that genes for cell-to-cell communication were co-opted

• uncertain whether earliest multicellular animals had a nervous system or whether it evolved in more derived animals

Sponges

• lack nervous systems but make homologs of proteins found in neurons

• hypothesized that sponge larvae use these proteins to build sensory cells to detect suitable places to settle and develop

Ctenophores Play Pivotal Role in Debate About Origins of Nervous Systems

• Hypothesis 1

  • nervous system evolved in common ancestor to all animals but was lost in sponges

• Hypothesis 2

  • nervous system evolved in ctenophores independently

  • evidence supports this one

Innate Behavior

• is behavior that’s genetically hardwired in an organism and can be performed in response to a cue without prior experience

  • ex. Tinbergen’s gull beak color

Synaptic Plasticity Allows for Learning

• is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity

• occurs when the number or strength of synaptic connections between neurons is altered in response to stimuli

Earliest Fossil Evidence of Brain

• Haikouichthys ~530mya

Vertebrate Brains are Divided into Specialized Regions

• Somatosensory cortex

  • proprioception

  • exteroception

  • interoception

• Broca’s area

  • speech

• Visual cortex

• Cerebellum

  • maintaining balance

• Brain stem

• Amygdala

  • emotional responses

• Hypothalamus

  • homeostasis

• Prefrontal cortex

  • attention

  • thought

  • perception

  • episodic memory

Vertebrate Brain Organization is…

relatively conserved

Evolutionary Stable Strategy

• a behavior that, when adopted by the majority of the population, cannot be invaded by another strategy

Dilution Effect

• refers to the safety in numbers that arise through swamping the foraging capacity of local predators

Cooperative Foraging

• wild dogs benefit more from hunting in packs than hunting on their own

Group Defense Cost

• group living comes at the cost of an increase of parasite load (contact)

Benefits of Sociality

• increased vigilance

• dilution effect

• enhanced defense

• cooperative foraging/hunting

• improved defense of critical resources

Costs of Sociality

• increased conspicuousness to predators

• increased competition for food

• increased competition for mates

• decreased certainty of paternity/maternity

• increased transmission of disease/parasites

Direct Fitness

• an organism’s own success in transmitting alleles to future generations

Indirect Fitness

• reproductive success of other individuals carrying the same alleles

Inclusive Fitness

direct fitness + indirect fitness

Kin Selection

• selection arising from the indirect benefits of helping relatives

Kin Selection in Ground Squirrels

• Belding’s ground squirrels

  • females don’t disperse very far (unlike males)

  • females more likely to give alarm calls

Kin Selection in White-Fronted Bee-Eaters

• White-Fronted Bee-Eaters

  • sometimes help parents during first 2 years of life

  • during harsh environmental conditions

Certainty of Paternity Makes Parental Care Profitable

• male giant water bugs

  • carry eggs on the back and aerate them by rocking back-and-forth on the water surface

  • only accept eggs from females after they have mated with them several times

Kin Recognition

• kin recognition can be challenging for males

• organisms may recognize kin through:

  • physical proximity

  • physical features or odors