Populations- distribution and abundance

Learning goals:
* understand the basic framework of what makes up a population
* be able to describe the factors that determine the distribution and abundances of populations
* understand the possible underlying reasons for the disperson of individuals within a population

Populations are dynamic, varying in size over time and space
Population defined as a group of individuals of the same species that live within a particular area at the same time

measures of abundance
size (number of individuals);
density (number of individuals per unit area)

What constitutes an individual in a population?  Many species can reproduce asexually, producing semi-autonomous individuals, while others are derived from sexual reproduction.  Individuals can be defined as products of a single fertilization: An aspen grove would be one individual, a genet.   Members of a genet may be independent physiologically, so members of a genet are called ramets

Abundance is dynamic- changes with time and across space
Influenced by both physical environment (e.g. climate variation) and biotic interactions (e.g. abundance of food or predators); Potential habitat may change in time and space

The distributions and abundances of organisms are limited by:
* habitat suitability
 * historical factors
 * and dispersal

Habitat suitability includes physical environment and biotic factors, such as availability of food, presence of predators and competitors; Species vary in their responses to variation in the physical environment; those with adaptations to a wide range of environmental conditions will tend to have wider geographic distributions
Biotic interactions can act to influence geographic distributions of populations, particularly at the margins of their tolerance to the physical environment
Biological control can be used to limit geographic ranges and abundances of pest species

History coupled with the limitations of dispersal may limit species geographic distributions; History includes a combination of evolutionary and geological events, such as where species evolved in relation to continental location; Historic dispersal barriers influence the distribution of species today

Species distributions can include seasonal migrations

Within their geographic range, species populations tend to be patchy, i.e. they occupy a smaller part of the area where they are found, due to microhabitat preference, distribution of prey, avoidance of predators
How individuals are arranged within a population provides hints about habitat preferences, dispersal, and biotic interactions
Dispersion is the spatial arrangement of individuals within a population- 3 basic possibilities:
Regular -individuals are evenly spaced
Random -individuals scattered randomly
Clumped - the most common pattern
Regular dispersion suggests competitve or territorial interactions among individuals
Clumped dispersion results from habitat preference, cooperative behavior among individuals, or short dispersal distances
Random dispersion suggests no microhabitat preference nor any biotic interactions among individuals-