Population dynamics
it deals with the way populations are affected by birth and death rates, and by immigration and emigration, and studies topics such as aging populations or population decline.
Population size
A population’s size depends on how the population is defined;
· If a population is defined in terms of some degree of reproductive isolation, then that population’s size is the size of its gene pool.
· If a population is defined in terms of some geographical range, then that population’s size is the number of individuals living in the defined area.
Ecologists typically are more concerned with the latter means of defining a population since this is both easier to do and is a more practical measure if one is interested in determining the impact of a given population on a given ecosystem, or vice versa.
Although we can determine an average population size for many species, the average is often of less interest than the year-to-year or place-to-place trend in numbers.
Population density
Population density may be defined as number of individual organisms per unit area. Different species, of course, exist at different densities in their environments, and the same species may be able to achieve one density in one environment and another in different environment.
Population densities may additionally be determined in terms of some measure other than population size per unit area such as population mass per unit area.
Population Distribution:
Individual members of populations may be distributed over a geographical area in a number of different ways including
· Clumped distribution (attraction)
· Uniform distribution (repulsion)
· Random distribution (minimal interaction/influence)
Clumping may result either from individual organisms being attracted to each other, or individual organisms being attracted more to some patches within a range than they are to other patches, the net effect is that some parts of the range will have a large number of individuals whereas others will contain few or none.
A uniform distribution means that approximately the same distance may be found between individual organisms; uniform distributions result from individual organisms actively repelling each other.
A random distribution means that where individual organisms are found is only minimally influenced by interactions with other members of the same population, and random distribution are uncommon; “Random spacing occurs in the absence of strong attractions or repulsions among individuals of a population.”
Comments
Post a Comment