Lecture 8 Flashcards
Give some examples of area-based counts
. All organisms in an area counted (could use a helicopter) or a quadrat subsample taken, and population size estimated by multiplication. Can be applied to volume sampling (e.g. take in 100m^2 air and multiple)
What are the two techniques to estimate population abundance and distribution?
. Area-based counts
. Distance-based methods
It is hard for biologists to count every animal so what do they use?
Equations
What is population growth limited by?
Intraspecific competition
Interspecific competition
What is competition?
. All growing plant or animal populations eventually subject to intraspecific competition
. Competition for resource (food, light, nutrients, water etc.)
. Populations have an upper sustainable limit- carrying capacity (K)
What is the the carrying capacity (K)?
Population size that can be maintained indefinitely- stable population size)
Describe the four key characteristics of intraspecific competition (have to be able to show all of these 4 otherwise it is not intraspecific competition)
. First- Decreased contribution of individuals to subsequent generations
. Second- the resource(S) for which the individuals are competing must be in limiting supply. This can be light, food nutrients, prey, water
. Third- Reciprocity must be present. This is where all the competing individuals are essentially the same (no significant differences between individuals)
. Four- density dependence
Explain what the key characteristics of intraspecific competition, decreased contribution of individuals to subsequent generations
A decrease in contribution of individuals to subsequent generations compared to the max if no competition (have to compromise reproduction).
This decrease in the contribution must be measurable in terms of decreased survivorship
Give an example of the impact on fecundity one of the key characteristics of intraspecific competition, competition is decreased contribution of individuals to subsequent generations
Song sparrows on Mandarte island.
The number of young per female that survived to independence declines with population density. The more breeding (density) pairs the more cramped- the more breeding females the less young they can reproduce.
In an experiment conducted at the high population densities observed in 1985, nesting pairs that were fed reared more young to independence than pairs that were not fed.
Give some examples of exceptions to one of the key characteristics of intraspecific competition, reciprocity must be present
. Reciprocity not present in many birds of prey chicks (unlike passerines). Insurance egg- if it’s an abundant year the chick will survive if it is not then it won’t
. Another example is some desert species of amphibians, such as spadefoot toads, which show alternative phenotypes (‘phenotypic plasticity’) to cope with unpredictable arid climates
. Another example is that food is limiting supply in the number of pairs great tits can produce
Explain the example of lack of reciprocity (when trying to determine if intraspecific competition is present) Arizona Spadefoot toads
Unstable desert environments with short breeding period when there is occasional rainfall (come together and breed whenever it rains). Carnivorous and herbivorous tadpoles. 2 different types of tadpoles that have a different phenotype but the same genotype.
So it is difficult to say for definite that intraspecific competition is happening
Give the example of a lack of reciprocity (when trying to determine whether intraspecific competition is present) hatching asynchrony in birds
. Many birds of prey- dependent on supply of small mammals to feed young
. ‘Boom’ and ‘busy’ population sizes
. Hatching asynchrony allows an ‘insurance egg’ (laid a little later, will survive if a good year, won’t if not): in poor years some chicks will fledge, in food years all will survive. Some of the chicks are stronger than others, the chicks born first will be stronger than the insurance egg
Explain the key characteristics of intraspecific competition, density dependence
Very important: the impact of competition is greater the higher the number of competitions present.
Number of deaths increase with population size
Give an example of a species that is affected by the key characteristics of intraspecific competition, density dependence
Soybean planting density and survivorship
Give the key characteristics of density dependence (important to regulate populations size around a fairly stable value)
. Intraspecific competition and density dependence are obviously closely linked
. When there is intraspecific competition its effects on survival and/ or fecundity is density dependent
. Not all density dependent effects arise from intraspecific competition i.e. interspecific competition, predation, parasitism and disease can be density dependent
. Density dependent effects usually refute the population size
