Term
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Definition
| Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment. (EX - flood, fire, hurricanes). From OUTSIDE community. |
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Term
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Definition
| The repeatable change in community composition through the time following a disturbance - in plant communities, driven by internal dynamics (involves species replacements, community changes) |
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Term
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Definition
| A relatively predictable series of successional changes following a disturbance (fire in Yellowstone) - in Yellowstone, there is self-thinning and trade-offs in life history traits |
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Term
| Self-Thinning in Yellowstone |
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Definition
The density of lodgepole pine trees increases dramatically during early succession, but then declines during mid succession and remains low during late succession.
This is because after a fire, some areas have many pine cones - where many trees sprout - over time the stronger trees outcompete neighbors for resources like light, and poor competitors die (thinning)
Due to intraspecific competition |
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Term
| Early Successional Species Traits |
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Definition
| Some species have roots/seeds that survive fires, or some need fires to sprout. Other seeds disperse quickly. Others may grow in the light now where there are no longer large trees. |
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Term
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Definition
| The differences in physiology and behavior that make each species well suited to grow in particular environments. |
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Term
| Trade-offs with life-history traits |
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Definition
| One cannot have a rapid growth in both high/low environments. Species that do well in early succession have different life-history traits than those that appear in late-succession. |
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Term
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Definition
| Changes in species composition are driven solely by internal dynamics |
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Term
| Catastrophic disturbances |
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Definition
| Remove all traces of previous communities |
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Term
| Facilitation (primary succession) |
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Definition
Succession occuring after catastrophic disturbance.
Makes following assumptions:
1) Barren ground is uninhabitable by all but the most stress-tolerant of colonists
2) Early colonists make environment more suitable for successive species by increasing nutrient availability, developing soils, reducing pH, providing shade from sun/shelter from wind
- Sequence continues until only most competitively dominant species no longer facilitate the invasion and growth of any other species.
lightening - small - medium - large |
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Term
| Facilitation (secondary succession) |
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Definition
Disturbance is not catastrophic
A few individuals survive the disturbance - speed up facilitation |
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Term
| Inhibition (secondary succession) |
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Definition
All species arriving on an unoccupied site can survive - initial composition = who gets there first
- once a colonist becomes established, it inhibits the growth of other arrivals by monopolizing resources
- when space/resources are released through the death or decay of other residencts, colonists can invade
- short-lived species die more frequently, succession slowly progresses from short to long lived species |
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Term
| Tolerance (secondary succession) |
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Definition
Intermediate between facilitation and inhibition models
- all species can survive on unoccupied site
- species that appear later arrived later/arrived early but grew more slowly
- late arriving species can tolerate the presence of early species and grow despite the presence of early successional species because they are better competitors for light/nutrients
- over time, better competitors exclude other species
- early successional species have no effect on late successional species |
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Term
| Comparison of facilitation, inhibition, tolerance |
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Definition
After disturbance opens space...
F: Only early successional species can colonize
I: any species can establish
T: any species can establish
...other early successional species is
F, I, T: reduced
...later successional species is
F: enhanced
I: prevented until existing individual dies
T: unaffected |
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Term
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Definition
External factors such as immigration by new species, seasonal changes in weather and sunlight, and disturbances affect communities as much, or more, than internal dynamics
Ensure that communities are almost never in equilibrium |
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Term
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Definition
Repeated disturbances - defined in terms of timing, magnitude, frequency, predictability
Red River's disturbance regime is characterized by predictable spring floods |
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Term
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Definition
| Where the flow of energy begins in simple food chains - first trophic level - vast majority are plants that use energy from the sun to power photosynthesis |
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Term
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Definition
Indirectly affect other members of the community by altering the environment and resource availability (beavers) - impact the success of other species
Must alter the availability of environmental resources - may also redistribute or transform living/non-living materials |
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Term
| Elk herbivory hypothesis - why aspens are declining in yellowstone: |
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Definition
| Thousands of elk eat aspen - when the wolves disappeared, elk numbers increased, decreasing aspen numbers. |
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Term
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Definition
| Top trophic level limits the size of the trophic levels they consume - wolves remove elk, so aspen increases until its growth is limited by availability of resources |
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Term
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Definition
A specific type of top-down effect in which the impacts of adding or removing a top carnivore cascade down to affect primary producers at the bottom of the food chain
When one trophic level is removed from an ecosystem, the following trophic levels are all affected - sea otter eats sea urchin, so kelp levels increase |
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Term
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Definition
In risky sites, foraging will be less efficient than in safer areas because the forager spends more time being vigilant and less time feeding
When wolves were reintroduced to Yellowstone - the elk began to avoid certain areas where wolves were dominant, thus their levels did not decrease significantly - fed in upland sites with clear escape paths |
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Term
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Definition
Gerbils will spend more time foraging in safe areas than risky ones
Remove more seeds when owls are not present
The foraging behavior of gerbils was affected by their perception of risk |
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Term
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Definition
| Ecosystem engineers that change the environment through their own physical structures - architecture of trees alters conditions on forest floor - produce shade, limit sunlight, reduce temp below canopy |
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Term
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Definition
| Animals that alter the environment by directly redistributing or transforming living/non-living materials (beavers, gophers) |
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Term
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Definition
Communities are structured by resource availability. Organisms on each trophic level are resource limited - if more energy is moving throughout a community, then each trophic level should include more individuals, and be able to support more individuals (more trophic levels)
# trophic levels = resources available. - community structure dpeends on supply of plant resources like nutrients, water, sunlight |
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Term
| Productivity Hypothesis - bottom up |
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Definition
| The more productive ecosystems have longer food chains - lakes with higher phosphorus concentrations would have longer food chains but that lake size would not matter |
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Term
| Ecosystem-size hypothesis - bottom up |
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Definition
| Food-chain lengths should increase with ecosystem size - rests on the observation that as ecosystem size increases, species diversity, haibtat diversity, habitat availability increase. Larger lakes have longer food chains - but phosphorus concentration would not matter. |
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Term
| Productive-space hypothesis - bottom up |
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Definition
| Combines productivity and ecosystem size hypotheses and argues that both productivity and ecosystem size are important. Food chain length would increase with both phosphorus concentration and lake size. |
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Term
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Definition
How much a community will change given a specific disturbance. More resistant - change less
Why differences? Plants with long, deep roots have a firmer hold that plants with short roots
Dense areas are stable - well-anchored sand dunes are less likely to be washed away by hurricanes |
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Term
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Definition
| The amount of time it takes for a community to stop changing (reach equilibrium) after a disturbance |
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Term
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Definition
How closely does the post-recovery community resemble the pre-disturbance community
High resilience - same community dynamics
Medium - same species but the relative abundances have changed
Low - different species, different relative abudances |
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Term
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Definition
The overall degree to which a community stays the same over time, especially after disturbances
High resilience, high resistance, small return time would = high persistence |
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Term
| Alternative Stable States |
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Definition
Different potential communities in the same place, occur when more than one type of community can exist in a particular environment
Lakes subject to nutrient pollution (nitrogen runoff) - as nutrient addition increases, some lakes pass threshold nutrient level and switch from clear-water state to cloudy-water state - switch is abrupt
The lake has reached an alternative stable state. |
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Term
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Definition
| Communities where predator-prey interactions cause a community's populations to be relatively stable than those with population sizes that swing widely. |
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Term
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Definition
| A niche is the constellation of environmental conditions under which a species can survive. Any place that satisfies the tolerance of a species for the relevant factors defines a niche for that species. |
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Term
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Definition
C = number of actual links/(number of species)^2
= L/S^2
S^2 because if every species could eat every other species (including its own)
C equals proportion of the total possible predatory connections in the community that actually exist
More species can be removed from communities with high connectance without causing additional species to go extinct compared to low connectance communities.
Species loss = lower community resilience, reduced ability to withstand further species loss |
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Term
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Definition
| Species that are the most abundant in a specific community - responsible for most of the community's primary production and physical structure |
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Term
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Definition
| Species that cause a disproportionate effect on their community for the size of their population; aka, there are not many of them in the community, but removing them causes drastic changes. |
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Term
| Community Importance (measurement) CIi |
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Definition
The change in a quantitative community or ecosystem trait that results from a change in that species abundance i.
CIi = (tN - tD)/ tN * (1/pi)
tN = trait in the intact community
tD = trait when species i has been removed |
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Term
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Definition
The magnitude of change that results when a species has been removed, regardless of the direction of the change.
TIi = (Ci)pi
pi = proportional biomass of i before it was removed |
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Term
| Importance of Community Importance/Total Importance Indicator |
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Definition
Indicates whether a species' impact is greater or less than would be expected based solely on its proportional abundance pi. If a species' importance is in direct proportion to pi then CI would either be +1, or -1. If its abs(CI) = 1, but its TI is high - dominant species
If abs (CI) is much greater than 1, the species is more important than pi would predcit. If TI is also >> pi would predict, it is a keystone species |
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Term
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Definition
| Species that colonize an area - humans have increased the rate of new species being introduced into existing ecological communities. |
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Term
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Definition
| Communities with higher connectance should be more stable |
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Term
| Diversity-Stability Hypothesis |
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Definition
| Species-rich communities are more stable |
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Term
| Competitive Exclusion Principle |
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Definition
| No two species can coexist in exactly the same ecological niche - if two species are using exactly the same resources, one of them is expected to win the competition and drive the other to extinction |
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Term
| Fundamental niche vs. Realized niche |
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Definition
| Fundamental - where they could live, realized - where they DO live |
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Term
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Definition
| Occurs when multiple individuals are attempting to acquire the same resources. While they are not actively fighting one another off, they indirectly compete because each individual obtains less of the resources due to the presence of the other individuals. |
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Term
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Definition
When interactions result in impeding access to a resource
Does not need to be a direct fight over a resource - some bird species will attack and destroy eggs in nests near their own, presumably to reduce competition for resources.
Barnacles - grow onto the top of other nearby barnacles, smother them and take their space on the rock |
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Term
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Definition
Plants interfere with one another directly, through the release of poisons
The poisons wash into soil - inhibit plant growth of other species |
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Term
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Definition
Individuals will establish territories and exclude other individuals to protect the resources within a territory
"resource" may be females
Maintained to protect breeding opportunities, monopolize access to good food sources, good shelters, other similar resources |
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Term
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Definition
Determined by whoever finds a resource first - barnacles compete with each other for space on rocks in the ocean - when an empty space opens up, individuals that settle there first has an advantage in colonizing that space
Plants compete for space and light
How is it different from exploitation?
Mesquite competes by growing expansive root systems that render large areas void of resources over time. The first plants there compete premptively, but the older plants compete by exploitation. |
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Term
| Intraspecific Competition |
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Definition
Competition between individuals of a specific species
Strongest when the individuals share the same limited resources
Some will outcompete others
Effects strongly whether a population will grow or shrink |
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Term
| r (overall population growth rate) |
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Definition
r = b-d (birth rate - death rate)
rm = intrinsic rate of growth - a population with unlimited resources will grow exponentially at a rate of rm. |
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Term
| Equation for growth rate given graphed data |
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Definition
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Term
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Definition
The size at which the resource limitation prevents population growth.
The resources available to the population are exactly equal to the resources required to sustain that population |
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Term
| Limiting Resources (examples) |
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Definition
| food, space, chemical nutrients, sunlight availability, other factors |
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Term
| Exponential Growth Equation |
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Definition
dN/dt (instantaneous rate of change)= rmN
rm = maximum rate |
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Term
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Definition
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Term
| Interspecific Competition |
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Definition
| Between species competition |
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Term
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Definition
| Add bacteria to your body to outcompete pathogenic strains - they are non-harmful bacterial strains |
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Term
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Definition
The competition coefficient is the per capita effect of one species on the population of the other species - represented by a
a for probiotic bacteria's effect on pathogenic bacteria = 2. |
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Term
| Logistic Growth Equation (with Competition) |
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Definition
| dN/dt = rmN1(1-(N1+a21N2)/K1) |
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Term
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Definition
| The equilibrium population sizes are not dependent on initial population sizes |
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Term
| Stable Coexistence (isoclines) |
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Definition
Occurs when K1
Two species can only coexist if intraspecific competition is stronger than interspecific competition |
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Term
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Definition
General approach is used to explore whether an observed pattern is due to environmental effects or interactions between species
Grow both species under same conditions "same garden" |
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Term
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Definition
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Term
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Definition
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Term
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Definition
| Two species may evolve in ways that reduce the strength of competition between them through opposing shifts along some trade-off. (Darwin's finches) |
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Term
| "Neutral" Theory of Biodiversity |
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Definition
Stephen Hubbell
Species distributions change randomly over time - every now and then species go extinct randomly, and every now and then a species randomly differentiates
Quite controversial
Cannot explain coral distributoins in coral reefs
Useful null hypothesis for other theories of coexistence |
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Term
| Effect of Algae/Cyanobacteria on Lakes |
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Definition
Massive algal blooms can choke/stagnate the water, establishing a barrier to the exchange of gases between the lake and the atmosphere - die en masse and increase the decompisition rate - decreases the amount of dissolved oxygen
Also lowers visibility - lower chance that fish can find one another to mate |
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Term
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Definition
Nutrients required by all organisms
Carbon - cell and tissue structure
Nitrogen - amino acids, nucleic acids
Phosphorus - amino acids, nucleic acids, ATP
Sulfur - amino acids, proteins (enzymes)
Oxygen
Hydrogen |
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Term
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Definition
Essential nutrients required in smaller amounts
zinc
iodine
potassium
iron |
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Term
| Factors that affect a plant's survival/competitive vigor (nutrients) |
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Definition
| Nutrient availability, species-specific nutrient requirements, and effectiveness of each plant's nutrient-capturing strategy |
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Term
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Definition
| Particular nutrients are in short supply in many ecosystems - limited availability of these nutrients limits how fast plants and animals can grow and reproduce |
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Term
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Definition
delta (Storage)= Inputs - Outputs
So in the case of the tree and nitrogen, Inputs = nitrogen from ground, Outputs = decomposition of tree (drops leaves or branches) |
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Term
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Definition
Nitrogen is removed from the soil pool and returned to the atmosphere
Plants uptake some of the nitrate produced during nitrification while the rest is converted back into N2. |
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Term
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Definition
Nitrogen from the atmosphere is added to the soil nitrogen pool
Bacteria convert N2 into inorganic forms plants can use
Lightening can provide energy to break bonds, fire release fixed N to atmosphere
Humans - burning fossil fuels releases NOx into the atmosphere where it reacts to form acid rain |
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Term
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Definition
Process by which same nutrients are constantly reused within the biosphere. Rate depends on relative pool and flux sizes.
Tight Cycling - when rate of cycling between internal compartments is high (uptake, decomp rates are large), compared to the fluxes in and out of system (fixation and denitrification) |
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Term
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Definition
| The pattern of input, internal cycling, and output (discussed earlier with tree) occurs microscopically (inside single-celled organisms), global level, all scale in between. |
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Term
| Atmospheric Nitrogen and Nitrogen Cycling |
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Definition
| Plants cannot utilize atmospheric nitrogen (strong triple bond leaves it inert) - they must rely on microorganisms to "fix" atmospheric nitrogen and convert it into forms that plants can use. Plants use it as ammonium, nitrate, or nitrite |
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Term
| Chemistry of Nitrogen Fixation |
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Definition
N2 + enzyme nitrogenase reduces N2 to NH3 - nitrogenase is inhibited by O2 - requires anaerobic environment
Further reduced to make NH4+ |
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Term
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Definition
After inorganic nitrogen entering an ecosystem is fixed it is converted into organic compounds by plants and microorganisms -
ammonium compounds combine with organic acids to form amino acids and proteins, most is stored in organic form that is not available for uptake by plants
Nitrogen enters soil via dead plant and animal matter, plant residues, animal waste - amount of plant-available nitrogen in the soil affects the net primary productivity, the amount of nitrogen in plant tissue |
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Term
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Definition
With lower available soil nitrogen, plants store less in their tissues, lowers litter quality and less nitrogen is available to decomposers. Microbial decomposers immobilize more nitrogen when it is more limiting in the soil - the amount of ammonium and nitrate available to plants is further reduced
When soil nitrogen contenct is high, a positive feedback loop exists that increases plant-available soil nitrogen |
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Term
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Definition
| The opposite of immobilization - when dead organisms and animal waste decompose, the organic forms of nitrogen contained in that material are converted back into ammonia and ammonium |
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Term
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Definition
Ammonium compounds are converted into nitrites and nitrates, nitrogen species - more soluble than ammonium, more mobile
Nitrifying bacteria - may not only be bactera - in oceans it is done by Archaea. |
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Term
| Chemical steps of Denitrification |
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Definition
NO3- is transformed back into nitrite NO2-
Nitrite is converted into NO and then N2O
Nitrous oxide is converted to N2. |
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Term
| How the Chemical Properties of Nutrients affect how they move via water flow: |
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Definition
NH4+ ions are positively charged, and soil contains negatively-charged clay particles. Positives attract negatives, ammonium binds tightly to clay particles
NO2-, NO3- do not bind, and they are easily dissolved in water.
Why they are more mobile in water |
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Term
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Definition
The process of converting nutrients from a solid to dissolved form that leads to loss from the system
Decreases soil fertility and causes nitrogen enrichment of water bodies located downstream |
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Term
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Definition
pH is equal to 4.5 or lower.
Caused by the release of acid-forming gases, primarily sulfur dioxide SO2 and nitrous oxides NOx. Human activites cause them - they react with water vapor to form sulfuric and nitric acids |
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Term
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Definition
pH of water falls below 5, fish cannot survive
soils with naturally high pH can buffer initial impact of acid rain
Forests are most sensitive - acid precipitation damages leaves and needles, reducing trees ability to photosynthesize or withstand cold
Reduces vitality/ability to regenerate |
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Term
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Definition
Does not include a substantial atmospheric component
Exists in sediments and mineral deposits
Weathering of rocks releases phosphorus into terrestrial and aquatic ecosystems
Mined for fertilizers, industrial processes, detergents
artificial transfer of phosphorus is 5x that of normal weathering
Enrichment of aquatic systems leads to sudden blooms of phytoplankton and aquatic vegetation. |
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Term
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Definition
All living things are built mostly from carbon
But living world accounts for tiny fraction of total carbon
99% of the Earth's carbon is in rocks, limestone, and cycles slowly
Major fluxes of carbon involve less than 1% of the total carbon on Earth, mostly CO2.
CO2 can dissolve in water - biggest CO2 pool is in deep ocean
Plants take up CO2 during photosynthesis, virtually all organisms release CO2 during respiration
Decomposers release much of the remaining carbon is the organisms' tissues
Do not decompose everything- so soil accumulates carbon over time
Two major carbon pools on land - aboveground biomass (wood of trees), in soils (carbon is stored in dead material) |
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Term
| Increasing World Affluence Scenario |
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Definition
Globally high economic growth - energy demands are met by a mix of energy sources, including some that release CO2 and some that don't
As the world becomes more affluent, population growth is expected to decline |
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Term
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Definition
| Global economic growth is both moderate and regional. Wide differences between countries economies continue, and population growth is continuous throughout the century |
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Term
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Definition
| Governments successfully reduce income and social inequalities and increase environmental conservation, resulting in cleaner technologies. Population peaks mid-century and then declines. |
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Term
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Definition
Some level of carbon is unaccounted for - the outputs do not equal inputs
Demonstrates that we do not fully understand the processes that control the carbon fluxes - our knowledge of cycle is not complete. |
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Term
| Effect of greenhouse gases |
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Definition
They trap radiation emitted from the earth's surface, warming the atmosphere
Northern Hemisphere winters will become warmer and wetter, sea levels will rise |
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Term
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Definition
lambda = N(t+1)/Nt
t is time
N is population size
Thus, Nt+1 = lambda^t*Nt |
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Term
| Exponential Growth equation (2) |
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Definition
Nt = No e^(rt)
r = ln(lambda)
r>0, population is increasing
r<0, population is decreasing |
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Term
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Definition
As the population size gets bigger and bigger, the change in population size per change in time also increases. This is capture by both geometric and exponential growth equations.
Assuming growth rate remains constant, as N gets larger, the change per unit time in the population also increases |
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Term
| Density-Dependent Factors |
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Definition
Influence population growth depending on the current size of the population. When the local population is large, they have a greater effect on that population.
food, light, space, disease, predation, parasitism |
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Term
| Density-Independent Factors |
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Definition
The impact of these factors on population growth remains the same regardless of the size of that population.
A storm passing through kills the same proportion of the population regardless of the size of that population.
Furthermore, after a density-independent event, the population can always recover back to its original carrying capacity, if given enough time. |
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Term
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Definition
| Fluctuation in which a population repeatedly overshoots and undershoots its carrying capacity by similar amounts. |
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Term
| Evolutionary Stable Strategy |
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Definition
| A strategy which when adopted by most members of the population cannot be beaten by any other strategy in the game. |
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Term
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Definition
cooperate on the first move and then do whatever your opponent did on their last move
1) It is retaliatory
2) It is forgiving |
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Term
| Plot of Moose Nutrient Constraints |
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Definition
Intake of aquatic plants on y, Intake of terrestrial plants on x
On downward sloping line is energy constraint, one horizontal line is sodium constraint. Another downward sloping line is Rumen constraint
Must be beneath rumen, above others
leaves a potential triangle
Anywhere in this triangle is possible |
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Term
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Definition
| If you are distasteful, it pays to be conspicuous to advertise the fact |
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Term
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Definition
The waiting game
Should you wait for a female or leave to look for more females elsewhere?
Payoff for A = V-mb
Payoff for B = -mb |
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Term
| Examples of Animal Contests |
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Definition
Serious fights - occur when the pay-off for winning is high
Respect for Ownership - respect for those who reach female first, when ownership is unclear more contests
Influence of resource value - matters more to organism, fight harder |
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Term
| Three hypothesis for Why Owners Win |
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Definition
1) They are better fighters
2) They have more to gain from a fight and are prepared to fight harder
3) Arbitrary asymmetry of ownership settles the contest - Bourgeois game
For tits, hypothesis 2 wins |
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Term
| Contests of Strength (deer stags) |
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Definition
Roar, walk, fight
Displays involved are reliable signals of strength and size, and involve degree of cooperation between the contestants
Contests proceed in set pattern |
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Term
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Definition
| Information gathering - the more closely matched the contestants the longer the assessment. |
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Term
| The Asymmetric War of Attrition |
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Definition
Va/Ka < Vb/Kb means that individual A gives up
V - Value of resource to individual
K - fighting ability |
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Term
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Definition
Displays that demonstrate reliable assessment of strength
Add color to sparrows, it doesn't change their behavior |
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Term
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Definition
Most often monogamous with biparental care
Able to feed twice as many young as single parent |
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Term
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Definition
| Usually polygynous - harems of females because females are predisposed to care - prolonged gestation, female lactates, etc |
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Term
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Definition
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Term
| Paternal Certainty hypothesis |
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Definition
External fertilization means high reliability of paternity
Internal - not so sure
Male is less willing to provide care in internal internal fertilization |
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Term
| Order of gamete release hypothesis |
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Definition
When males must wait for eggs to be laid before fertilization, the female has an opportunity to desert and swim away
Rejected on empirical grounds - simultaneous release is most common |
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Term
| Association hypothesis (mating systems) |
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Definition
Association with embryos adapts a sex for parental care
Internal - female is most closely associated with embryo
External - eggs are laid in male's territory and male is most closely associated with embryos
Defence of territory = defence of eggs and young, equals parental care |
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Term
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Definition
| The extent to which parental care of individual offspring reduces the parent’s residual reproductive value: any characteristics or actions of parents that increase the fitness of their offspring at a cost to any other component of the parent’s fitness. |
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Term
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Definition
| any form of parental behavior that appears likely to increase the fitness of that parent’s offspring. |
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Term
| Parent-offspring conflict |
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Definition
| over PI (Parental Investment) leads to selection arenas and analyses of weaning and sex-allocation, e.g. in chimpanzees. |
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Term
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Definition
| over PI leads to analysis of pregnancy conflicts mediated by genomic imprinting in humans. |
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Term
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Definition
| over PI leads to analysis of brood reduction, e.g. raptors, hyenas. |
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Term
| Reproductive success if allocating to mate guarding |
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Definition
pG (SG/(SG+S)) + (1-pG)
pg - Risk of sperm competition
sg - Sperm produced per mating
sg+s - Proportion of
eggs fertilized
1-pg - Probability of no
sperm competition |
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Term
| Reproductive success if allocating to sperm production |
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Definition
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Term
| Guarding leads to higher success when... |
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Definition
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Term
| Group selection is implausible but not impossible because... |
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Definition
1. The correlation between traits and reproductive success is often much weaker for groups than for individuals.
2. Variation in reproductive success among individuals is often greater than variation in reproductive success among groups. The potential strength of individual selection is therefore normally much greater than the potential strength of group selection.
3. The amount of genetic variation in a trait that can be accounted for by differences among individuals is normally much larger than the amount that can be accounted for by differences among groups. The potential response to individual selection is therefore normally much larger than the potential response to group selection.
4. The generation time of individuals is often much shorter than the generation time of groups, and the number of individuals is much larger than the number of groups. Therefore the number of incidents of selection on individuals in a unit of time is very much larger than the number of incidents of selection on groups.
5. Individuals are discrete things with measurable reproductive success; the boundaries of groups in space and time are often diffuse. |
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Term
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Definition
If what matters is not individual survival but an increase in frequency of the genes carried by an individual, then it will pay an individual to sacrifice itself if more copies of that individual’s genes then get into the next generation than if the individual did not sacrifice itself.
The costs and benefits of the act thus have to be weighed against each other in genetic currency.
Genes exist not only in the individual but also in its relatives.
Therefore if an individual can help its relatives to survive and reproduce, and if the increase in the number of its genes in the next generation through offspring of relatives thus caused is greater than the decrease through its own offspring that results, then helping behavior will be selected. |
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Definition
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Term
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Definition
Group size increases the capacity of group members to catch, produce, or defend food;
to detect or repel predators;
to disperse in large subgroups, reducing dispersal mortality;
to raise young successfully;
and to compete against other groups.
Individuals living in smaller groups often have slow growth rates, low survival, and low breeding success; hence small groups frequently become extinct. |
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Term
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Definition
An exchange of fitness-increasing benefits between two individuals.
In each act of reciprocity, an actor incurs some fitness cost (c) and a recipient receives some benefit (b).
As reciprocal interactions between two individuals continue, both achieve a cumulative fitness gain. b - c > 0 (n.b. measured in different individuals)
Repeated encounters between the same two agents
Traits that favor reciprocal altruism
good memory (learning)
individual recognition
spatial contiguity
Comes down to long-term self-interest
(and a disincentive to cheat) |
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