Population Ecology

1. Population Ecology

2. Characteristics of Populations Population: a group of individuals of a single species that simultaneously occupy the same general area Two important characteristics of any population are density and the spacing of individuals Density: the number of individuals per unit area of volume

3. Dispersion: the pattern of spacing among individuals within the boundaries of the population The mark-recapture method can be used to measure population density N= number in 1st catch X total in 2nd catch number of recaptures in 2nd catch

4. 3 Patterns of Dispersion Clumped: the individuals are aggregated into patches ex. mushrooms, animals that move in herds Uniform: evenly spaced; may result from direct interactions between individuals ex. territorial behavior, competition

5. Characteristics of Populations

6. Random: occurs in the absence of strong attractions or repulsions Demography is the study of factors that affect the growth and decline of populations - additions occur because of birth and immigrations

7. - eliminations occur because of deaths and emigration Life tables are used as a summary of the survival patterns of a population - survivorship curves plot the data for a life table - type 1 curve: low death rate during early and middle ages; drops steeply with age

8. - type 3 curve: high death rate among young, then flattens out as death rate declines for adults ex. marine invertebrates - type 2 curve: mortality is constant over lifespan ex. annual plants, grey squirrel

9. Characteristics of Populations

10. Life History Life histories are diverse, but they exhibit patterns in their variability - big-bang reproduction: some plants and animals invest most of their energy into growth and development, and then expend their energy in 1 large reproductive effort; also called semelparity

11. Life History

12. Life History - repeated reproduction: organisms produce fewer offspring at a time, but do so over many seasons; also called iteroparity - limited resources mandate trade-offs between investments in reproduction and survival

13. The exponential model of population growth describes an idealized population in an unlimited environment Change in pop size = births – deaths DN/Dt = B-D Scientists use r to represent the difference in per capita birth and death r = b-d

14. Zero population growth (ZPG) occurs when the birth rate equals the death rate ( r = 0) Intrinsic rate ( rmax) is the fastest growth rate possible reproducing under ideal conditions

15. Exponential growth is a population increase under ideal conditions dN/dt = rmaxN - the population increases rapidly - J shaped growth curve

16. The logistic model of population growth incorporates the concept of carrying capacity Carrying capacity: the maximum population size that an environment can support - symbolized as K - when N = K, the growth rate = 0

17. Population Growth Carrying capacity Number of Yeast Cells Time (hours)

18. Population-limiting factors Factors that limit growth are both density-dependent and density-independent Density dependent: death rate will rise as the population density rises - predation-prey - competition for food

19. Population-limiting factors

20. Population-limiting factors Density independent: birth and death rates do not change with density - mainly caused by weather and climate - not caused by negative feedback