the study of the interactions of living things with each other and their physical environment

Ecological Organization Organism Population Community Ecosystem Biome Biosphere

Population Ecology

Population: all the members of a species inhabiting a given location.

One characteristic of a population is its population density.

Population Density: the number of organisms per unit area. The population density of egrets is greater near the water buffalo than it is away from the water buffalo. Population density depends on many factors: reproductive patterns, food availability, competition etc.

Factors that Affect Population Density Limiting Factors Abiotic Factors v. Biotic Factors Density Dependent v. Density Independent Factors Reproductive Patterns

In all environments, organisms with similar needs may compete with each other for resources, including food, space, water, air, and shelter. These factors that can limit the size of a population are called limiting factors. They can be divided into categories: Abiotic or Biotic and Density- dependent and Density-independent. .

Abiotic Factors NONLIVING FACTORS those physical and chemical factors which affect the ability of organisms to survive and reproduce EXAMPLES: intensity of light range of temperatures amount of moisture type of substratum (soil or rock type) availability of inorganic substances such as minerals supply of gases such as oxygen, carbon dioxide, and nitrogen pH NONLIVING FACTORS

Examples of Abiotic Factors What abiotic factors might affect the survival of these plants?

Examples of how abiotic factors determine population density. A low annual temperature common to the northern latitudes determines in part the species of plants which can exist in that area. 2. The amount of oxygen dissolved in a body of water will help determine what species of fish live there. 3. The dry environment of desert regions limits the organisms that can live there.

Living factors in an organism’s environment. Biotic Factors LIVING FACTORS Living factors in an organism’s environment. Thus, the organisms, their presence, parts, interaction, and wastes are all biotic factors. EXAMPLES: LOOK AT THE SALMON HABITAT  What biotic factors might be in the habitat? - algae, subaquatic vegetation, microscopic organisms, migratory birds that fly over the stream.

Population Limiting Factors Limiting factors keep a population from increasing indefinitely. There are two categories of limiting factors. > Density-independent Factors > Density-dependent Factors

Density-Independent Factors Any factor in the environment that does not depend on the number of members in the population. Examples: Weather events such as drought, flooding, extreme heat or cold, tornadoes, hurricanes, and fire. Human activity such as building dams, water diversions, barriers, introducing nonnative species, and pollution. TYPICALLY ABIOTIC FACTORS

Density-Dependent Factors Any factor in the environment that does depend on the number of members in the population. Examples: Predation, disease, parasites, competition for food TYPICALLY BIOTIC FACTORS

Carrying Capacity the maximum number of organisms the resources of an area can support The carrying capacity of the environment is limited by the available abiotic and biotic resources, as well as the ability of ecosystems to recycle the residue of dead organisms through the activities of bacteria and fungi.

Steady State Occurs when the population remains relatively constant over a number of years. This will occur when the number of births equals the number of deaths.

Population Growth Curves Exponential Growth Model: population grows without any limits placed on it by the environment. Logistic Growth Model: population stops growing exponentially when it reaches its carrying capacity.

Exponential Growth Curve Slow growth period (lag phase) at first, and then rapid growth J - shaped curve All populations grow exponentially until limiting factors slow the growth.

Logistic Growth Curve Population growth slows or stops following its exponential growth Reaches carrying capacity Birth is less than death S – shaped curve Population levels off

Boom and Bust Growth Curve “Booms” characterized by rapid growth which is followed by “busts” during which the population falls back to a minimal level.  

Reproductive Patterns R – Strategists: small organisms, short life spans, many offspring. Ex. Mice K – Strategists: larger organisms, long life span, produces few offspring, nurture young. Ex. Elephant

R - Strategists Live in environments where food, temperature and other factors fluctuate. Reproduce as many offspring as possible in a short period of time. Expend little to no energy in raising their young to adulthood. They usually do not maintain a population near the carrying capacity.

K - Strategists Produce a few offspring that have a better chance of reaching reproductive age because of the energy, resources and time invested in nurturing the young. Carry-capacity changed little from year to year.