Download Characteristics of Populations

APES CHARACTERISTICS OF POPULATIONS
Changes in population size, density, dispersion, age structure and sex ratio are known as population
dynamics.
The most common pattern of population dispersion found in nature is a clumped pattern.
Population dispersion may be affected by
 Immigration
 Emigration
 Mating habits
 Seasonal changes
Population dispersion in an ecosystem is often determined by the distribution of resources.
Age structure categories include
 Pre-reproductive
 Reproductive
 Post-reproductive
Population size is governed by births, deaths, immigration, and emigration.
The biotic potential of a population is the maximum reproductive rate of the population.
Biotic potential is determined by
 Reproductive age span
 Litter size
 How many offspring survive to reproductive age
 How often reproduction occurs
Rapidly growing populations in nature may be limited by
 Light
 Water
 Space
 Nutrients
Environmental resistance is enhanced by a specialized niche.
A population will increase if the biotic potential increases.
Carrying capacity refers to the maximum size of population the environment will support.
The curve depicting the growth of a population that is limited by a definite carrying capacity is shaped
like the letter “S”.
A population crash occurs when a population overshoots its carrying capacity and environmental
pressures cause effects.
One reason why a population may overshoot its carrying capacity is due to a time delay.
The human population of Ireland experienced a major crash as a result of a potato fungus.
Humans have extended the Earth’s carrying capacity for the human species by
 Controlling many diseases
 Using energy resources at a rapid rate
 Using material resources at a rapid rate
 Increasing food production
Carrying capacity is determined by
 Climatic changes
 Migration
 Predation
 Interspecific competition
Density dependent population controls include
 Human destruction of habitat
 Parasitism
 Competition for resources
 Predation
Studies of populations of mice indicate that overcrowding is associated with
 Reduced milk production in nursing females
 Lower sexual activity
 More spontaneous abortions
 Inhibited sexual maturity
Density-independent population controls include
 Drought
 Fire
 Floods
 Unfavorable chemical changes in the environment
Some general types of population curves are
 Stable (monkeys in a rainforest)
 Cyclic (muskrats after trapping has been outlawed)
 Irruptive (rabbits and coyotes in undisturbed habitat)
REPRODUCTIVE STRATEGIES AND SURVIVAL
r-strategists
 Are generally is small and short lived
 Insects, aquatic organisms (fish and invertebrates)
 Exhibit early-loss survivorship curves
K-strategists
 are generally less adaptable to change than r-strategists
 have populations that follow an S-shaped growth curve
 large mammals
 exhibit late-loss survivorship curves
Extinctions
There have been (5) mass extinctions 20-60 million years apart during the past 500 million years
The last mass extinction occurred about 65 million years ago
Adaptive radiation usually follows mass extinctions