Download Population Numbers - Effingham County Schools

Population Numbers
AG-WL-6
Population Dynamics
 Short and long term changes in the size and age composition of populations, and the
biological and environmental processes influencing these changes
 Deals with the way populations are affected by birth and death rates, and by immigration
and emigration, and studies topics such as aging or population declines
Population Dynamics may change due to…
 Reproduction rates
 Social conflicts
 Movements of animals
 Ecological succession or disturbance
 Death
Qualities that Define Welfare of Wildlife
 Age Structure
 Proportional amount of young and old age classes
 Can be depicted by a “triangle”
 Lots of young on the bottom and very few old on the top
 Age may be measured in years, weeks, or days
 Young and very old experience the highest mortality rates
 Lifespan
 Different species have different lifespans
 Species towards the end of the food chain are usually much longer-lived
 Combination of lifespan and age structure explain general health of population
 Sex Ratio
 Each species has an “ideal” sex ratio
 Appropriate sex ratios will maximize the ability of a species to produce new individuals
Qualities that Define Welfare of Wildlife
 Natality & Mortality
 Reflects pressures to increase and decrease population size
 Migration
 Winters and dry seasons result in less available food and water
 Animals will migrate to accommodate the seasonal fluctuations
 Carrying Capacity
 When most species approach their carrying capacity, mortality factors overtake natality and the
population will decline
Limits to Population Size Around Carrying Capacity
Theoretical maximum rate of growth of a population is
limited by factors that restrict the reproduction and
survival of individuals
Density Independent Factors
Any limit on a population that is not related to the population
numbers
 Natural Forces – fire, storms, flooding, tornadoes, volcanoes, etc.
 Weather Changes – periodic cold weather in temperate climates
 Human Activities – heated water discharged by power plants can impact 100% mortality on fish;
chemicals accidently or intentionally released into the environment
 Habitat Destruction – roadways, farms, suburbs, factories, cities, etc.
Density Dependent Factors
Any limit on a population that is related to the population
numbers
 Predation – organisms must hunt and kill others for nutritional needs
 Competition – cover, water, food, breeding sites, and space
 Physically unfit are particularly affected
 If organisms are forced to colonize, poorer habitats, death from starvation, disease, or predation
may occur
 Parasitism – organisms that feed on tissues of other organisms are more easily transmitted
among individuals when the population density is high
 Disease – populations may be severely depleted by disease because the transportation
distance between carriers is reduced
Factors Affecting Natality
 Habitat
 Minimum breeding age
 Maximum breed age
 Number of young produced per year
 Length of life after maximum breeding age
 Sex and age composition of the population
 Mating habitats related to age and sex compositions of the
population
Biological Surplus
A scientific name for the number of animals in a given
populations that are above the carrying capacity
 Most game animals have high biological surplus
 If animals are being harvested or dying faster than they can be replaced, the number of
breeding animals will be reduced, and the herd or flock will not be able to sustain its
numbers
 It is important to have enough mature animals to produce offspring and enough offspring
to replace maturing animals as they die
Biological Surplus
 If 25 deer exist in a habitat with a carrying capacity for 25, and 12
fawns are born and 2 adults die of natural causes, the new
population will be 35.
 The biological surplus for the deer populations will be 10.
 The 10 deer will either move to other areas or will die of starvation, disease,
predators, or hunting
 Those 10 deer are the extra and can be removed without changing the
overall population
Biotic Potential
 Maximum reproductive capacity of a population if resources are unlimited
 Can only be reached when environmental conditions are very favorable
 A species reaching its biotic potential would exhibit exponential population growth and
be determined to have a high fertility rate
Biotic Potential Influences
 Age at which reproduction begins
 Time the species remains reproductive
 Number of offspring produced during each period of reproduction
Activity
Raptor Population Ecology