Ethology and Behavioral Ecology.
I. Terms and Concepts
Behavior: The response of an organism to signals from the environment.
Behaviors can be examined from a proximate (how) and an ultimate (why) perspective.
Are behaviors adaptive? Do they have a genetic basis?
Natural selection will favor behavioral traits that promote individual reproductive success as measured by the number of offspring that live to reproduce (the individual's personal fitness).
Ethology: the study of behaviors from the point of view of adaptation.
Instinct OR innate behavior: genetically programmed behavior that requires no learning.
Complex versions of this are known as fixed action patterns, which are typically triggered by some sign stimulus.
e.g. tail feathers in precopulatory position in male and female red-wing blackbirds.
e.g. death feign in hog-nosed snake (Photo below; See also figure 60.1 in Raven & Johnson).
Innate behaviors generally don't respond much to an animal's life experiences.
Learning: a change in behavior due to experience.
The ability to learn is closely related to the complexity of an animals nervous system.
Classical Conditioning - an association is formed between some normal body function and a stimulus, resulting in a reflex.
E.g. Pavlovian response in dogs.
Operant Conditioning - learning in which an animal is rewarded or punished for performing a behavior.
E.g. Rats in Skinner box trial by error learning.
Imprinting - learning that occurs only during a critical period.
The process of imprinting is genetically determined, but the particular object to be imprinted on is learned. Mother-offspring imprinting is perhaps the most common. Based on work of Konrad Lorenz 1973 Nobel Prize in Medicine.
Habituation - learning that allows an animal to ignore repeated irrelevant stimuli.
II. Behavioral Ecology
Behavioral Ecology is the study of how animals interact with their environment, and the survival value of behaviors. Often focuses on the efficiency of a behavior and on its relative costs and benefits compared to other possible behaviors.
One the main premises of behavioral ecology is that all behaviors are assumed to have great survival value - otherwise the processes of natural selection (discussed a few lectures back) would have selected against it and removed it from the population.
A consequence of this assumption is that behavioral ecologists assume that behaviors are optimally adapted to at least some component of their environment. The challenge therefore is to find out what aspect of the environment is selecting against all other forms of this behavior other than what we find. (Remember that we discuss the actions of natural selection in double negatives, as in "not selected against".)
For example:
- Why do some animals live in groups while others do not (evolution of sociality)?
- Why do animals eat some types of food but not other types (optimal foraging strategies)?
- Why do some animals leave the region in which they were born (dispersal strategies)?
- Why do some animals act as helpers while others do not (kin selection and reciprocal altruism)?
study how behavior serves as an adaptation and alters an animals reproductive success study how natural selection shapes behavior use a cost-benefit analysis of the behavior relative to alternate forms of the behavior (or of solving the problem) to determine the value of the behavior for natural selection generate testable hypotheses have dominated the field of animal behavior for the last 20+ years
These are "why" or
ultimate questions, (as contrasted with the "how" or
proximate questions) that we discussed last lecture)
traceable to Niko Tinbergen, 1973
co-Nobel prize winner.
e.g. Digger wasps and nest-locating behavior using a ring of pine cones and stones
- uses artificially placed ring of pine cones to locate nest
- when the ring of cones is moved, the wasp will go to the center of the ring, even though the nest entrance is not there
- if the ring of cones is changed into a triangle and a ring of rocks is placed near the cones, the wasp will go to the center of the ring, not the the triangle - they therefore remember the arrangement, not the materials of their markers
Proximate or Mechanistic question: How do they use their environment cues to locate their nest?
Hypothesis or Answer: They use the arrangement and distribution of their cues, rather than the material of the cues themselves or the absolute location of the nest in space, to find their nest easier.Ultimate or Evolutionary question: Of what use is it to fitness if they use their environmental cues to locate their nest?
Hypothesis or Answer: Helps to maximize the fitness of the wasp so that she can optimally use her time and energy to rear the maximum number of offspring
Behavioral ecology often focuses on the efficiency of a behavior and on its relative costs and benefits compared to other possible behaviors.
e.g. Optimal Foraging theory
- Organisms are hypothesized to gather and process food optimally
- To be suboptimal would be to waste either the time and energy of the animal, or it may have access to less of the resource than if they had foraged optimally
- An Example:
- Capture, handling, digestion - all potentially costly activities in the acquisition of nutrients
- All should be done optimally so as to minimize their costs and maximize the benefits (both measured in calories)
e.g., Bluegill sunfish feeding on Daphnia of different sizes at different prey densities
- At low densities, there was little selectivity
- At high prey densities, there was significant selectivity for feeding on larger prey sizes
- This minimizes capture and handling costs and maximizes payoff to the fish
Why do some animals live in groups and others do not?
To answer this, ask:
- What are the costs and benefits of group-living?
- Is there variation in the behavior for natural selection to work?
- Is there an optimal group size, and if so do animals live at this group size?
- Can we tie the concept of the Tragedy of the Commons to optimal group size?
Hardin, G. The Tragedy of the Commons. Science, 1968. 162:1243-8.- When living in groups, who should one live with?
Mixed-species flocks - of what use is it to flock with birds who are not of a feather?
How are cooperative and altruistic behaviors maintained within groups?
- Kin Selection and Inclusive Fitness (W.D. Hamilton).
- "I would give my life for two brothers or eight cousins" J.B.S. Haldane
- e.g., scrub jays
- Reciprocal Altruism (R.D. Trivers).
- not all individuals that assist are genetically related - e.g.,
- you scratch my back, I'll scratch yours in the future
Why do male birds have inordinately developed plumage in many species?
Sexual selection (Darwin)
- Often seemingly works in opposition to natural selection, in that the trait would produce a form of the trait that may shorten the lifespan or survivability of the individual
- However, if it does promote their cumulative reproductive output to a greater level than they would have attained, had they lived longer but acted differently, then it will enhance their genetic contribution to the next generation relative to others (what is the term for this?) as well.
A Question For The Road: Can this field also apply to plants and other non-animals, or is this solely an animal focused field? Do plants have behavior? If so, can these actions be inherited?
Updated
March 22, 2005
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