1. Ecology – Population Growth and Regulation
Ecology – the study of interrelationships among living things and their nonliving environment
Environment – 2 components:
Abiotic – nonliving (soil, water, weather, pH)
Biotic – living (all forms of life)

2. Levels of Organization:
Population – all members of a particular species who live within an ecosystem, interact with one another and can potentially interbreed
Community – all the interacting populations in an ecosystem
Ecosystem – all the organisms and their nonliving environment within a defined area (prairie, forest)
Biosphere – the part of the earth inhabited by living organisms; includes both living and nonliving components

3. Populations Population density – number of individuals/unit area
Measuring density
In rare cases, population size and density can be determined by counting the actual number of organisms
Usually done by random sampling
Common method used is the mark-recapture method (read in textbook)

4. Population distribution – the spatial pattern in which members of a population are dispersed within a given area
Clumped – members of a population live in groups (herds, flocks, schools)
Advantage includes more individuals to find food, large groups confuse predators
May clump due to resource availability (cotton trees cluster along streams, animals around water holes)
Uniform – organisms maintain a relatively constant distance between individuals
Common in animals that are territorial
Helps ensure adequate resources for each individual
Random – patternless and unpredictable, occurs in the absence of strong attractions or repulsions among individuals, resources equally available (more rare) ex. Trees and plants in rainforest

5. Population growth – determined by three factors: births, deaths, and migration (immigration – migration into a population; emigration – migration out of a population)
(births – deaths) + (immigrants – emigrants) = change in population size
Ultimate size of a population results from a balance between opposing factors:
Biotic potential – maximum rate at which the population could increase, assuming ideal conditions that allow a maximum birth rate and minimum death rate
Environmental resistance – limits set by the environment such as availability of food, space, competition, predation, and parasitism

6. Biotic Potential
Growth rate (r) – measure of the change in population size per individual per unit of time
b d = r
(birth rate) (death rate) (growth rate)
To determine number of individuals added to a population in a given time period, growth rate (r) is multiplied by original population size (N)
population growth = rN

7. Biotic Potential
Exponential growth – pattern of continuously accelerating increase in population size – forms a J-curve
Example: bacteria under ideal lab conditions could produce enough bacteria to form a foot deep layer over the entire Earth starting with just one cell dividing every 20 min.

8. Biotic potential is influenced by:
Age at which the organism first reproduces
Frequency with which reproduction occurs
Average number of offspring produced each time
Length of organism’s reproductive life span
Death rate of individuals under ideal conditions
Biotic potential helps ensure that at least one offspring survives to bear it’s own young
In nature, exponential growth occurs only for a limited time

9. Regulation of Population Growth
Population size is limited by environmental resistance (such as available resources)
Boom-and-Bust cycles – populations characterized by rapid growth followed by a sudden massive die-off
ex. Algae, insects – have seasonal cycles linked to rainfall, temperature, nutrient availability
Insects grow during spring and summer and die with the frost

10. S-curves – after a period of growth, populations tend to stabilize at or below the max number the environment can sustain
Reaches a state of equilibrium with growth rate of zero
Carrying capacity – max population size that an ecosystem can support indefinitely
Typical of long-lived organisms

11. Limiting Factors – 2 Major Types
Density independent – limit size of population regardless of population density
Weather (causes boom and bust cycles), human activity (pesticides, pollution, habitat destruction), natural catastrophes (flood, fire, hurricane)

12. Density dependent – limit size of population as population density increases
Major limiting factor for long-lived species
Examples include:
predation and parasitism – control prey/host populations
Competition for limited resources
Intraspecific competition – among individuals of the same species (very intense, impt in natural selection)
Interspecific competition – among individuals of different species
Usually, if two species niches overlap too much, will lead to Competitive Exclusion
Overcrowding may lead to physiological and behavioral changes that increase emigration

13. Competitive Exclusion Principle
Proposed by G.F. Gause (Gause’s Principle)
If two species niches overlap too much, one species will be better at getting the resources and the other will be eliminated

14. Mortality and Survivorship Curves
Populations show characteristics patterns of deaths or survivorship over time
1. Late Loss – show a convex shaped curve, relatively low infant death rates, most individuals survive to old age
Red curve
Ex. Humans, large animals

15. Mortality and Survivorship Curves
2. Constant Loss – individuals have a fairly constant death rate, have an equal chance of dying at any time during their life span
Black line
Ex. annual plants, hydra, some invertebrates, some rodents

16. Mortality and Survivorship Curves
3. Early Loss – show a concave curve, produce large numbers of offspring that receive little parental care, death rate is very high among offspring, those that become adults have a good chance of surviving to old age
Blue curve
Ex. Most invertebrates, plants, many fish

17. Life History
Traits that affect an organism’s schedule of reproduction and death
K- selected populations (species or strategists) and r-selected populations (species or strategists) represent hypothetical models

18. r-selected populations
Usually do not reach carrying capacity
Tend to live in unstable, temporary environments
Generally limited by density independent factors
Produce large numbers of offspring
Early loss survivorship curve

19. K-selected populations
Usually have slow or no population growth
Usually at or near carrying capacity
Live in stable predictable environments
Produce few young and provide parental care
Competition for limited resources limits population size
Late loss survivorship curve