Characteristics of a Population

1. Characteristics of a Population • Population - individuals inhabiting the same area at the same time • Population Dynamics: Population change due to • Population Size - number of individuals • Population Density - population size in a certain space at a given time • Population Dispersion - spatial pattern in habitat • Age Structure - proportion of individuals in each age group in population

2. Population Size • Natality • Number of individuals added through reproduction • Mortality • Number of individuals removed through death

3. Population Density • Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area • Some species exist in high densities - Mice • Some species exist in low densities - Mountain lions • Density depends upon • social/population structure • mating relationships • time of year

4. Population Dispersion Population dispersion is the spatial pattern of distribution There are three main classifications Clumped: individuals are lumped into groups http://www.johndarm.clara.net/galleryphots/

5. Uniform: Individuals are regularly spaced in the environment Random: Individuals are randomly dispersed in the environment www.agry.purdue.edu/turf/ tips/2002/clover611.htm Population Dispersion http://www.calflora.net/bloomingplants/creosotebush2.html

6. Age Structure • The age structure of a population is usually shown graphically • The population is usually divided up into prereproductives, reproductives and postreproductives • The age structure of a population dictates whether is will grow, shrink, or stay the same size

7. Population Growth • Population growth depends upon • birth rates • death rates • immigration rates (into area) • emigration rates (exit area) Pop = Pop0 + (b + i) - (d + e)

8. Population Growth • Populations show two types of growth • Exponential • J-shaped curve • Growth is independent of population density • Logistic • S-shaped curve • Growth is not independent of population density

9. Exponential Growth Graph

10. Population Dynamics and Carrying Capacity • Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)

11. Carrying Capacity (K) • Exponential curve is not realistic due to carrying capacity of area • Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

13. Logistic Growth • Because of Environmental Resistance, population growth decreases as density reaches carrying capacity • Graph of individuals vs. time yields an S-curved growth curve • Reproductive time lag causes population overshoot • Population will not be steady curve due to resources (prey) and predators

14. Density Dependent Limiting Factor • Only affects a population when it reaches a certain density (size). • Competition • Fighting for resources • Predation • Increase of predators in an area will limit the growth of prey

15. More… • Disease • High densities make it easier for parasites and diseases to find a host and spread. • Parasitism • More animals for the parasites…more parasites that are there to harm the host • Crowding • Over-crowding can cause a depletion of resources, disease and stress • Stress • Makes organisms weak and prone to diseases

16. Density Independent Factors • Affect a population no matter what the density is • Natural disasters • Droughts, floods, tornadoes, fires, hurricanes…they don’t care how many organisms are in an area • Temperature • Determines which organisms can survive • Sunlight • Can only penetrate up to 30 m of water.

17. More… • Human Activities • Habitat destruction, hunting, pollution… • Physical Characteristics • adaptations • Behaviors • Migration, societies, feeding areas…

19. Reproductive Strategies • Goal of every species is to produce as many offspring as possible • Each individual has a limited amount of energy to put towards life and reproduction • This leads to a trade-off of long life or high reproductive rate

20. Conservation Biology • Careful and sensible use of natural resources by humans • Originated in 1970s to deal with problems in maintaining earth's biodiversity • Dedicated to protecting ecosystems and to finding practical ways to prevent premature extinctions of species

21. Conservation Biology • Three Principles • Biodiversity and ecological integrity are useful and necessary to all life on earth and should not be reduced by human actions • Humans should not cause or hasten the premature extinction of populations and species or disrupt vital ecological processes • Best way to preserve earth’s biodiversity and ecological integrity is to protect intact ecosystems that provide sufficient habitat

22. Habitat Fragmentation • Process by which human activity breaks natural ecosystems into smaller and smaller pieces of land • Greatest impact on populations of species that require large areas of continuous habitat • Also called habitat islands

24. 1949 1964 Habitat fragmentation in northern Alberta 1982 1991

25. Human Impacts • Fragmentation and degrading habitat • Simplifying natural ecosystems • Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides • Elimination of some predators

26. Human Impacts • Deliberately or accidentally introducing new species • Overharvesting potentially renewable resources • Interfering with the normal chemical cycling and energy flows in ecosystem