chapter 11 behavioral ecology

behavioral ecology

interactions between organisms and their environment that are mediated by behavior.

• often focuses on animals (but more recently has expanded to studies of plants and microbes (show behavior, too)

• ex. see research on plant behavior by Dr. James Cahill in our department

what is behavior?

the internally coordinated responses (actions or interactions) of whole living organisms (individuals or groups) to internal and/or external stimuli

Different behaviors may be adaptive

Intraspecific and interspecific variation.

Intraspecific variation

behavior varies within a species

Interspecific variation

behavior varies between species

Adaptive behavior

a behavior that increases the fitness of an organism and will be selected for over multiple generations

• operate in range of conditions and depend on both genes and environment

behavior and genes

natural selection can only act on behavior if the behavior has genetic basis

distribution of work based on age

• younger bees inside hive (brood care)

• older bees outside of hive (forage)

• foraging behavior coded by single gene for which produces a specific protein kinase

• more PKG = work outside

• less PKG = work inside

Hamiton’’s 4 classes of social interaction

Cooperation, altruism, selfishness, and spite

Cooperation

Both donor and recipient benefit

Altruism

Recipient gets benefits, donor doesn’t

• ex. red squirrel individuals will adopt offspring of close relatives

• ex. ground squirrels alarm call when they see a predator warning kin but draw attention and increase their own risk of predation

Selfishness

Donor benefits, recipient doesn’t

• ex. from the perspective of the cowbird, laying eggs in other nests 

• obligate brood parasite must lay eggs in the nest of other birds

Spite

Neither donor nor recipient benefit

• ex. European badger individuals that are chronically infected with tuberculosis → leave kin (fitness disadvantage) -. spread pathogen to non-kin (fitness disadvantage also)

donor

individual performing the action

recipient

individual recognizing behavior

fitness

the number of offspring contributed by an individual relative to the number of offspring produced by other population members

Inclusive fitness

an individual’s overall fitness is determined by its survival and reproduction, plus the survival and reproduction of its relatives. 

• natural selection favors behaviors that increase the inclusive fitness of individuals

• if individuals that display a particular behavior ae selected for or against, there can be evolution within a population

Cooperation and selfishness

should be selected for by natural selection, because they increase donor fitness

altruism and spite

should be selected against by natural selection, because they decrease donor fitness

why would a donor commit to altruism?

• group selection

• manipulation

• reciprocal altruism

• kin selection

group selection

individuals neglect their own needs in favor of the needs of a group

manipulation

donor does not recognize it is being parasitized

reciprocal altruism

recipient will pay back at one point in the future

kin selection

individuals increase their inclusive fitness by helping increase the survival and reproduction of relatives (kin)

coefficient if relationship (Rg)

the probability that the alleles at a given locus will be identical by descent among two individuals in the population

• parent - self: 50% relatedness

• grandparent - child: 50% x 50% = 25%

Hamilton’s rule formula Altruistic behavior is expected if:

• Rg x B > C

• Rg x B - C > 0

• Rg = genetic relatedness of the donor and the recipient

• B = reproductive benefit gained by the recipient 

• C = reproductive cost of the donor

Hamilton’s Rule

The more distant the relationship, the smaller the coefficient of relationship (Rg), and the larger the benefits (B) must be outweigh the cost (C).

The closer the relationship, the larger the coefficient of relationship (Rg), and the smaller the benefits (B) must be outweigh the cost (C)

Selfishness: is the eastern phoebe being altruistic?

from the perspective of the phoebe, raising eggs from other species is altruistic behavior.

• often parasitized bird doesn’t notice

• this is manipulation, because the donor has no means to recognize/prevent the interaction

selfish herds

always trying to get into the middle of the herd. better them than you. 

Cooperation

• generally, within a species and often between related animals

• can involve exchange of resources, protection, etc.

• many examples described in animals

sociality

usually consists of group of individuals living together, involving some degree of cooperation between individuals

the evolution of sociality is generally accompanied by:

• cooperative feeding

• defense of the social group

• restricted reproductive opportunities

examples of social behavior

• mutual grooming

• group protection of young

• highly complex societies (ex. ants or bees)

• alloparenting/allonursing

cooperative breeders

• live in groups

• several adults help with offspring

  • defense

  • prepare/maintain living area

  • feed young

why cooperative breeders work

inclusive fitness and r

inclusive fitness

members of the group are most likely relatives

reciprocal altruism

“tit for tat” if you help the group, they will help you

eusociality

highly complex social behavior, that evolved independently across multiple organismal groups

eusocial animals usually have 3 major characteristics

• individuals of more than one generation live together

• cooperative care of young

• division of individuals into sterile/non-reproductive and reproductive castes

  • excludes cooperative breeding mammals except mole rat.

examples of eusocial animals

• leafcutter ants 

  • Range: central and south America

  • one of the most socially complex organisms

• naked mole rat

  • range: eastern Africa

  • one of two eusocial mammal (the other being the Damarland mole-rate, south Africa

why has eusociality evolved?

• kin selection may play role as individuals in colonies have very high degree of relatedness

• ecological constraints may play role (ex. defense and maintenance of burrow system)

Haplodiploidy

a sex determination system where males develop from unfertilized, haploid eggs (one set of chromosomes), and females develop from fertilized, diploid eggs (two sets of chromosomes)