1. Chapter 53 ~ Population Ecology

2. Dispersal and Distribution
Several factors influence where species occur and why species are found in certain places
Biotic factors – do other species limit the distribution of a species?
Abiotic factors – do nonliving factors limit the distribution of a species?
Temperature, water availability, oxygen levels, salinity, sunlight, rocks and soil (pH, mineral composition, ect)

3. Population Characteristics
Density - number of individuals per unit of area
Individual counts
Sample size estimate
Indirect indicators
Mark-recapture
Dispersion - pattern of spacing
Random: unpredictable, patternless spacing
Clumped: patchy aggregation
Uniform: even spacing

4. Animals often exhibit uniform dispersion due to territoriality behavior

5. Demography: factors that affect growth & decline of populations
Birth rate - number of offspring produced
Death rate - number of individuals that die in a population
Growth or decline in populations can be calculated by using the rate of change when comparing births and deaths
Change in population over time is birth rate minus death rate

6. Demography
Age structure diagram: relative number of individuals of each age and sex in a population at a given point in time

7. Age Structure Diagrams
Analysis of age structure diagrams can determine if the population is experiencing an increase, decrease, or no population change
A growing population would have higher numbers of younger ages indicating a high birth rate (true pyramid shape)
A declining population would have lower numbers in the pre- reproductive age groups compared to the reproductive ages
A stable population would have age groups generally the same lengths

8. Examples of Changes to Populations

9. Demography
Survivorship curve: plot of the fraction of a population still alive at each age or from one age to the next

10. Survivorship Curves
Type I = low death rates during early and midlife, then death rate increases sharply in older age
Ex: humans and most mammals
Type II = constant death rate over the organism’s life span
Ex: Belding’s ground squirrel, other rodents, some lizards, and some annual plants
Type III = very high early death rates, then a flat rate for the few surviving to older age
Ex: most marine invertebrates, some plants, many fishes

11. Population Growth Models
Models are used to describe the growth of populations
Per capita rate of increase (r)
Population ecologist are interested in the difference between the per capita (individual) birth and death rates and the effect on the population size
Basically, ecologist want to know how many new individuals will be added to the population each year and what the new population numbers will be
So, change in N (number in the population) over change in time = rN

12. Population Growth Models
Exponential model (blue)
Equation: dN/dt = rN
Idealized population in an unlimited environment
Utilized by r-selected species (r= per capita growth rate)
Populations accumulate more new individuals per unit of time when it is large than when it is small giving the graph a J-curve shape

13. Population Growth Models
Logistic model (red)
Equation: dN/dt = rN (K-N/K)
(K-N/K) represents the fraction of K that is still available for population growth
Carrying capacity (K): maximum population size that a particular environment can support which creates the S- curve shape
K-selected species utilize this type of model

14. Population Change
Population dynamics are influenced by population density and life history traits
Population limiting factors are either affected by or not affected by the density of a given population
Density-dependent and density-independent factors can limit population size in different ways

15. Population limiting factor examples
Density-dependent factors
Competition
Predation
Intrinsic factors – physiological responses within individuals to change reproductive rates
Territoriality
Waste accumulation
Disease
Density-independent factors
Weather/climate
Periodic disturbances

18. Life History
Life history includes traits that affect an organism’s schedule of reproduction and survival
3 Variables:
When reproduction begins and age of sexual maturity
How often the organism reproduces
Some organisms save their resources for one big reproductive event
Coral Spawning and Coral Spawning 2
The number of offspring during each reproductive event

19. Population life history strategies
r-selected
Maximize reproductive success in uncrowded environments (density- independent selection)
Short maturation & lifespan
Many (small) offspring; usually one (early) reproduction; no parental care
High death rate
K-selected
Sensitive to population density changes (density-dependent selection)
Long maturation & lifespan
Few (large) offspring; usually several (late) reproductions; extensive parental care
Low death rate