1. POPULATION

2. Dynamics of Natural Population
Populations of most species remain more or less constant.
Population Equilibrium: deaths = births

3. Dynamics of Natural Population
Population Growth Curves
Exponential increase results in Population Explosion
J-shaped curve (only happens when a disturbance occurs—foreign species, habitat change, removal of predator)
Growth is independent of population density
Also called geometric growth

4. Dynamics of Natural Population
Doubling Time
How long it takes to double a population
Doubling time (years) = 70/annual % growth
Annual % growth = (BR-DR)/10
Example
BR = 20 DR = 5
Annual % growth = (20-5)/10 = 1.5
Doubling time = 70/1.5 = 47 years

5. Dynamics of Natural Population
When a population exceeds the carrying capacity a population crash or dieback occurs
Overshoot: extent to which a population exceeds the carrying capacity
This pattern of population explosion then crash is called irruptive or Malthusian growth

6. Dynamics of Natural Population
Population Growth Curves
Logistic
S-shaped curve (population levels off and continues in a dynamic equilibrium)
Growth is not independent of population density
A more stable population

8. BIOTIC POTENTIAL Number of offspring that a species may produce
Recruitment: survival through earthy growth stages to become part of the breeding population

9. REPRODUCTIVE STRATEGIES
Malthusian “Strategies”
Produce massive numbers of young, but leave survival to nature
High biotic potential, but low recruitment (high mortality) so population may not increase
Examples: insects, rodents, marine invertebrates, parasites and “weeds”
R-strategists

10. REPRODUCTIVE STRATEGIES
Logistic “Strategies”
Produce less young, but care for them until they can compete for resources themselves
Usually are larger, live longer, mature more slowly and have fewer natural predators
Examples: wolves, elephants, whales and primates
K-strategists

11. Factors that Increase or Decrease Populations
Natality: number of individuals added through reproduction
Fecundity: physical ability to reproduce
Fertility: measure of the actual number of offspring produced
Immigration: organisms introduced into a new ecosystem

12. Factors that Increase or Decrease Populations
Mortality: or death rate
Number organisms that die in time period divided by number alive at beginning of period
Survivorship: percentage of a cohort that survives to a certain age
Life Expectancy: probable number of years of survival for an individual of a given age
Emigration: members leave a population

13. Life Expectancy In United States
1900—47.3 years
2004—77.6 years
Often varies with sex and race
Difference due to genetics, access to medical care, occupations, diet and behavior
Life Span: longest period of life reached by a given type of organism

14. Survivorship Curves
Late Loss: K-strategists that produce few young and care for them until they reach reproductive age thus reducing juvenile mortality
Constant Loss: typically intermediate reproductive strategies with fairly constant mortality throughout all age classes
Early Loss: r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age
Can also have early and late loss with high survival during reproductive years

16. Factors that Regulate Population Growth
Various factors regulate population growth, usually by affecting natality or mortality
Intrinsic: operating within individual organisms or between organisms in the same species
Extrinsic: imposed from outside the population

17. Factors that Regulate Population Growth
Biotic Factors:
Ability of animals to migrate or if seeds to disperse, to similar habitats
Ability to adapt to and invade new habitats
Defense mechanisms
Resistance to adverse conditions and disease
Abiotic Factors:
Light, temperature, nutrients, etc.

18. Environmental Resistance
Combination of all the biotic and abiotic factors that may limit a population’s increase
Replacement Level: when recruitment (young) = adults that have died

19. Carrying Capacity
The maximum population a habitat can support (sustainable)
If population greatly exceeds carrying capacity, it will undergo a J-curve crash
Population reaches max and then starts to decline because of lack of resources

20. Density Dependence/Critical #
Population Density: number of individuals per unit of area
Density Dependent: factors that change based on population density
Population increases, environmental resistance becomes more intense
Density Independent: factors not affected by population
Abiotic factors

21. Factors that Regulate Population Growth
Density-Dependent Factors:
Most are results of interactions between populations of a community (predation) but some are within a population
1)Interspecific Interactions
-predation helps prevent population overshoot
-predator/prey populations often oscillate known as Lotka-Volterra model
-mutualism and commensalism

22. Factors that Regulate Population Growth
2) Intraspecific Interactions
-population of a species can increase to carrying capacity but then start to compete with each other for resources
-territoriality (usually between members of the same species)

23. Factors that Regulate Population Growth
3) Stress and Crowding
-when population densities get high, organisms often exhibit symptoms of what is called stress shock or stress-related diseases
-physical, psychological and/or behavioral changes may occur if too much competition and too close proximity to other members of the same species

24. Factors that Regulate Population Growth
Density-Independent Factors:
Tend to be abiotic components
Examples: weather or climate
Abiotic factors can be beneficial—rainfall in deserts, fires in grasslands
These factors operate without regard to the number of organisms involved

25. Density Dependence/Critical #
Populations may not recover from low #s
Critical Number: minimum number of individuals a species needs to stay a healthy population
If population goes below this it will probably become extinct.

27. Mechanisms of Population Equilibrium
Predator-prey Dynamics
Herbivores and predators, Parasites, Plant-herbivore dynamics and Keystone species
Competition
Intraspecific (same species) and Interspecific (different species)
Introduced Species

28. Island Biogeography
Diversity in isolated habitats is a balance between colonization and extinction rates
Smaller islands farther from mainland have less colonization and fewer individuals of a species
Larger islands closer to mainland tend to have greater diversity

29. Conservation Genetics
Hardy-Weinberg equilibrium
In large populations, if mating is random, no mutations occur and there is no gene in-flow or selective pressure for or against particular traits, random distribution of gene types will occur
Different alleles will be distributed in the offspring in the same ratio they occur in the parents and genetic diversity is preserved

30. Conservation Genetics
In small, isolated populations immigration, mortality, mutations or chance mating events involving only a few individuals can greatly alter the genetic makeup of the population
Gradual changes in gene frequencies due to random events is called genetic drift

31. Conservation Genetics
Founder Effect or Demographic Bottleneck
occurs when just a few members of a species survive a catastrophic event or colonize new habitat geographically isolated from other members of the same species

32. Population Viability Analysis
Minimum viable population size
number of individuals needed for long-term survival of rare and endangered species

33. Metapopulations
A collection of populations that have regular or intermittent gene flow between geographically separate units
Some species exist in several distinct habitats and individuals occasionally move among these, mating with existing animals or recolonizing empty habitats