Chapter 54 - Behavioural Ecology

What can explain diverse behaviours

selection for individual survival and reproductive success

3 key questions for the evolution of foraging behaviour

1. where to forage

2. what to eat

3. when to search for pray

The optimal diet model

prey are ranked by benefit (usually energy) per unit of handling time

• top ranked prey are never rejected

  • lower-ranked prey may be rejected in the presence of more valuable food available

• ex. oystercatcher may choose medium-size mussels over large mussels because large mussels take too long to open

central place foraging

foraging from a central place (nest or a den when feeding offspring) to catch prey

prediction of central foraging theory

longer travel times are only worthwhile if you can bring back large more valuable prey

• ex. ospreys flying further to forage bring back larger fish to the nest

When to forage and examples

many animals schedule foraging to avoid predators

• ex. deer, mice, and kangaroo rats forage at night (nocturnally) to avoid daytime (diurnal) predators

  • but some predators like owls take advantage of nocturnal foraging prey

Mating behaviour and Mate choice

these behaviours include seeking or attracting mates, choosing among potential mates, competing for mates, and caring for offspring

2 types of Mating Systems

Monogamous and Polygamous

Monogamous Mating system

one male mates with one female

• males and females usually have similar external

Polygamous Mating System

an individual of one sex mates with several individuals of the other sex

• species in this system are usually sexually sexually dimorphic

  • males and females have different external morphologies

types of Polygamous Mating systems

• Polyandry - one female mates with multiple males

  • ex. phalaropes, angler fish

• Polygyny - one male mates with multiple females

  • ex. elephant seals, elk

• Polygynandrous - both males and females have multiple partners

  • ex. red-winged blackbirds

Mating Systems and Parental Care

mating relationship between males and females varies from species to species

• in many species, mating is promiscuous with no strong pair-bonds or lasting relationships

2 factors that affect the mating system and parental care

1. expensive offspring favour monogamy

2. certainty of paternity

How Expensive Offspring favour monogamy

favoured when offspring require much parental care (ex. altricial birds) and can’t care for themselves

• males benefit by staying with their partner

  • since they can produce more offspring that can survive better

• ex. in precocial birds where the young can feed themselves (like ducks and pheasants), males derive less benefit from staying with their partner

  • so they maximize reproductive success by searching for other mates

Importance of the Certainty of paternity

males can increase their reproductive success by:

1. helping a female to raise his offspring

2. searching for other mates

• males gain no evolutionary benefit if another male is the genetic parent of the offspring

• ex. male birds singing to attract mates are less likely to care for kids

how certainty of paternity affects parental care

certainty of paternity is lowest in species with internal fertilization

• and vice versa

• paternal care is more common in species with external fertilization like fish, amphibians, aquatc invertebrates

• ex. giant waterbug and plainfin midshipman

Types of sexual selection

• intersexual selection - members of one sex choose mates on the basis of certain traits such as plumage or colour

• intrasexual selection - competition between members of the same sex for mates, often by fighting

Female choice

type of intersexual selection

• where females drive sexual selection by choosing males with specific behaviours or features of anatomy

  • ex. female stalk-eyed flies choose males with long eyestalks

    • ornaments like long eyestalks or plumage of peacock often correlate with health and vitality

male competition

source of intrasexual selection that can reduce variation among males

• favours the evolution of weaponry and large body size

agonistic behaviour

may happen in male competition

• ritualized contest that determines which competitor gains access to a resource

types of midshipman males

Type 1 Males - more larger and vocalize when attracting females

Type 2 males don’t vocalize

weaponry (features) for fighting in salmon

• chum salmon are sometimes called '“dog” salmon because they have canine teeth that develop when spawning

• hooknose male in chinook salmon don’t feed on spawning grounds

  • canine teeth are for fighting with other males

genetic basis of behaviour

most behaviours have a genetic basis to some extent

• true for all humans

  • the big 5 personality traits (extraversion, agreeableness, openness, conscientiousness, neuroticism) show a high degree of variability

  • some behavioural variation can be linked to variation in a single gene, but most are controlled by many genes (polygenic)

example of mating systems and genetic basis of behaviour

mating system in prairie vs. meadow voles

• prairie voles are monogamous, which makes them unusual, while meadow voles are polygynous

• difference in male behaviour can be traced to the gene receptor for a neuropeptide hormone (vasopressin)

vassopressin

and also oxytocin (which is closely related)

• they are neuropeptides that play a key role in social attachment and affiliation including parental care and pair-bonding

influence of a single locus variation

differences at a single locus can sometimes have large effect on behaviour

• ex. male prairie voles pair-bond, while male meadow voles don’t

• level of a specific receptor for a neurotransmitter determines which behavioural pattern develops

Case Study - variation in Prey selection of Garter Snakes

natural diet of gartner snakes varies by population

• coastal populations - mostly feed on banana slugs

• inland populations - rarely eat banana slugs

• studies show that these differences in diet are genetic

  • causes them to differ in ability to detect and respond to specific odor molecules of banana slugs

Monoamine Oxidase A gene (and how it affects behaviour)

codes for an enzyme that breaks down neurotransmitters norepinephrine and dopamine

• single point mutation disables the gene that is located on X chromosome

  • males with the mutation (super rare) are cognitively impaired and prone to violence and sexual offences

• gene affects fight or flight responses

  • can respond inappropriately to minor stressors

Warrior genes

variant of monoamine oxidase A gene

• slow acting variant may result individuals being more prone to aggression / antisocial behaviour

• effect is conditional on early environment - having the gene doesn’t guarantee the behaviour, it depends on early environment

  • individuals raised in abuse environments show antisocial behaviour

  • individuals raised in nurturing environments show normal behaviour

twin studies and behaviour

allow researchers to compare relative influences of genetics and environments on behaviour

• monozygotic twins show more concordance (similarity) than dizygotic twins

• suggest that genes are important

altruism

when animals may behave in ways that reduce their individual fitness but increase the fitness of others

• ex. when under threat from a predator, Belding’s ground squirrel will alarm others, even if alarming others increases the chance that a killer is called towards him

William D. Hamilton

proposed Kin Selection and Hamilton’s Rule

Inclusive fitness

total effect an individual has on increasing number of its genes by producing offspring and helping close relatives produce offspring

• helps explain altruistic behaviour

• ex. workers (all females) in ants, bees, and wasps don’t reproduce

  • they assist close relatives to raise offspring

Concept of Relatedness

explains why the average relatedness of full siblings is ½

• there is a 50% chance that you will share an identical copy of a gene you received from one of your parents

3 variables in altruistic acts

B - benefit to the receipient

C - cost to the altruist

r - coefficient of relatedness

• fraction of genes that are shared on average

Hamilton’s rule

Natural selection favours altruism when

rB > C

Kin selection

an animal can increase its genetic representation in the next generation by helping close relatives (other than its own offspring) that share identical genes

• favours Hamilton’s rule by enhancing reproductive success of relatives

Case Study - inclussive fitness in Belding’s groun squirrels

female belding’s ground squirrels are more likely to call alarm in the presence of a predator than males

• alarm calling is dangerous since it attracts predators

• but in a group, most of the females are closer related to each other than males are

• kin selection benefit for calling is greater for females than males

Inclusive fitness in mole rats

Naked mole rats in a colony are closely related

• non-reproductive individuals increase their inclusive fitness by helping the reproductive queen and kings (and close relatives) to pass their genes to the next generation

human behaviour

results from interactions between genes and environment

• social and cultural institutions may provide the only feature where there is no continuum between humans and other animals

examples of adaptive human behaviours

• possess a language instinct

• acquire language automatically during an early critical period that lasts until around puberty

• tongue pushing in newborns

• during first months of life, infants push solid objects from mouth

  • this behaviour is adaptive because the digestive system is not yet ready for solid food

why do mothers gain weight during pregnancy

lactation is energetically expensive

• mothers add weight during pregnancy to pay for cost of lactation

• mothers of twins gain more weight than mothers of singletons

Incest avoidance

children raised together in the first 30 months of life usually show no sexual interest in one other

• this is adaptive because it avoids harmful effects of inbreeding

  • each of us carry two recessive lethal genes on average

Traits for which genetic basis is known

alzheimer’s, aggression, dyslexia, extraversion, general intelligence, sexual orientation, memory, verbal ability, obsessive compulsive disorder, novelty-seeking behaviour, shizophrenia, spatial abiility

• genes play a role in almost every behaviour, but no behaviour is 100% heritable

Parent-offspring conflict

concept that offspring should be more selfish than parents desire

• since parents and offspring have shared but not identical genetic interests

parent-offspring conflict in humans

human pregnancy is an example

• Preeclampsia - high blood pressure

• gestational diabetes

both are due to embryonic genes manipulating mother to increase food supply to the fetus

both involve imprinted genes (due to the dad)