1. Population Ecology

2. Environmental Variation
Key elements of an organism’s environment include:
temperature
water
sunlight
Soil
Classical limiting factors
Many organisms actively employ mechanisms to maintain homeostasis, while others conform to their environment.

3. Populations
A population consists of individuals of a given species living together at the same place at the same time.
Population distributions
Most species have a limited geographic range.
Population ranges change through time.
environment changes
organisms circumvent previously inhospitable habitat

4. Population Dispersion
Randomly spaced
Individuals are randomly spaced within a population.
Uniformly spaced
Uniform spacing within a population often results from resource competition.
Clumped spacing
Individuals clump into groups or clusters in response to uneven distribution of resources in their immediate environment.

5. Population Dispersion

6. Population Dispersion

7. Cost of Reproduction
A life history is the complete life cycle of an organism.
all involve significant trade-offs
Due to limited resources, increased reproduction may decrease survival and chances of future production.
cost of reproduction
Natural selection will favor the life history that maximizes lifetime reproductive success.

8. Cost of Reproduction Investment per offspring
Key reproductive tradeoff concerns the amount of resources to invest in producing any single offspring.
number of offspring versus size of each offspring
In many species, offspring size critically affects chances of survival.

9. Cost of Reproduction
Reproductive events per lifetime
semelparity - organisms focus all reproductive efforts on a single, large event
iteroparity - organisms produce offspring several times over many seasons
Age at first reproduction
Longer-lived animals tend to reproduce later, and provide more parental care than shorter-lived animals.

10. Demography Demography - statistical study of populations
Factors affecting growth rates
sex ratio
effect also determined by mating habits
generation time
average interval between birth of an individual and the birth of its offspring

11. Demography
Age structure
cohort - individuals of the same age
fecundity - number of offspring produced in a given period of time
mortality - number of deaths in a given period of time
Age structure determined by the relative number of individuals in each cohort.

12. Cohort and Age Structure of Baby Boomers

13. Demography
Life tables
constructed by following the fate of a cohort from birth until death
Survivorship curves
Survivorship is the percentage of an original population that survives to a given age.
Type I - full life span
Type II - mortality unrelated to age
Type III - early susceptibility

14. Survivorship Curves

15. dN/dt = riN Population Growth
Darwin recognized that organisms can out reproduce their environmental resources
Biotic potential - the rate at which a population of a species will increase when there are no limits on its rate of growth
Mathematical terms -
dN/dt = riN

16. dN/dt = riN Where: N = number of individuals in the population
dN/dt = the rate of change of population numbers over time
r = intrinsic rate of increase for that population (intrinsic capacity for growth)
r is difficult to calculate and is often considered as the difference between birth rate and the death rate

17. Biotic Potential Exponential growth model
Rate at which a population of a given species will increase when no limits are placed on the rate of growth.
Innate capacity for growth of any population is exponential.
Even when rate remains constant, actual increase in number accelerates as the population size grows.

18. Biotic Potential
Carrying capacity
Carrying capacity (K) is the maximum number of individuals the resources in a given area can support.
Logistic growth
As a population approaches carrying capacity, its growth rate slows as resources become depleted.
sigmoidal growth curve

19. The Carrying Capacity K

20. The Carrying Capacity K

22. The End