1. Population and Community Ecology

2. Population Characteristics
Density- # of individuals per unit of area
Determined by…
counts
sample size estimate
indirect indicators
mark-recapture
Dispersion- pattern of spacing
Types:
Random- unpredictable, patternless spacing (c)
Clumped- patchy aggregation (a)
Uniform- even spacing (b)

3. Immigration vs. Emigration
Movement into an area
Emigration
Movement out of an area

4. Demography: factors that affect growth & decline of populations
Birthrate (natality, fecundity)- # of offspring produced
Death rate (mortality)
Age structure- relative number of individuals of each age
Survivorship curve- plot of numbers still alive at each age

5. Types of Survivorship Curves
Type I
Relatively low death rates until later in life
Ex: humans
Type II
Constant death rate throughout lifespan
Ex: lizards
Type III
More death of young individuals
Ex: Sea turtles

6. Population Growth Models
Exponential model (blue)  
idealized population in an unlimited environment (J-curve)
r-selected species (r=per capita growth rate)
Logistic model (red)
carrying capacity (K): maximum population size that a particular environment can support (S-curve)
K-selected species

7. Mathematical Models N = population size t = time Exponential Growth
d = discrete/fixed time interval
r = per capita rate of increase
r = births – deaths
If r > 0, population is growing
If r < 0, population is declining
K= carrying capacity
Exponential Growth
Logistic Growth

8. Life History “Strategies”
r-selected (opportunistic)
Short maturation & lifespan
Many (small) offspring; usually 1 (early) reproduction; no parental care
High death rate
K-selected (equilibrial)
Long maturation & lifespan
Few (large) offspring; usually several (late) reproductions; extensive parental care
Low death rate

9. Population Limiting Factors
Density-dependent factors
competition
predation
stress/crowding
waste accumulation
Density-independent factors
weather/climate
periodic disturbances

10. Community Ecology Community
an assemblage of populations living close enough together for potential interaction

11. Community Structure Richness (number of species) & abundance
Species diversity
Hypotheses:
Individualistic- chance assemblage with similar abiotic requirements
Interactive- assemblage locked into association by mandatory biotic interactions

12. Interactions
Interspecific- interactions between populations of different species within a community:
Predation
Includes herbivory and parasitism
Competition
Commensalism
Mutualism

13. Predation Defense Cryptic (camouflage) coloration
Aposematic (warning) coloration
Mimicry- superficial resemblance to another species
Batesian- palatable/ harmless species mimics an unpalatable/ harmful model
Mullerian- 2 or more unpalatable, aposematically colored species resemble each other

14. Competition: a closer look
Interference- actual fighting over resources
Exploitative- consumption or use of similar resources
Competitive Exclusion Principle- 2 species with similar needs for the same limiting resources cannot coexist in the same place
Gause experiment

15. The Niche
Ecological niche- the sum total of an organism’s use of biotic and abiotic resources in its environment; its “ecological role”
Fundamental- the set of resources a population is theoretically capable of using under ideal conditions
Realized- the resources a population actually uses
2 species cannot coexist in a community if their niches are identical

16. Competition Evidence Resource partitioning- Character displacement-
sympatric species consume slightly different foods or use other resources in slightly different ways
Character displacement-
Allopatric species are similar
Sympatric species show morphological differences

17. Species Richness and Diversity
Total number of different species
Relative Abundance
Proportion each species represents of the total individuals

18. Trophic Structure Transfer of food energy through a community
About 10% of the energy can be transferred from one level to the next
Food Chain- linear feeding relationship
Food Web- shows all the possible feeding relationships

19. Arctic Food Web

20. Special Species Dominant Species Keystone Species Foundation Species
Most abundant
Keystone Species
Strong control on community structure
Not necessarily most abundant
Foundation Species
Cause physiological changes to community

21. Succession
Ecological succession- transition in species composition over ecological time
Primary
begun in lifeless area; no soil, perhaps volcanic activity or retreating glacier
Secondary
an existing community has been cleared by some disturbance that leaves the soil intact