Scales of Ecological Organization

Distribution and Abundance Relationships between Populations Population Dynamics Distribution and Abundance Relationships between Populations

Populations A population is a group of individuals of the same species living in the same area. Species features are important to their location

Populations Distribution is the area that one or more members of the same species are found Three patterns found: uniform, clumped, and random. Species have a dispersion pattern which indicates where the species are found. Random Uniform Clumped

Population Growth All populations undergo three distinct phases of their life cycle: growth stability decline Growth - when available resources exceed the number of individuals using them. Reproduction is rapid, and death rates are low, producing an increase in population size.

Population stability is often followed by a "crash" Stability is longest phase Decline is the decrease in the number of individuals in a population can lead to extinction. since the growing population eventually outstrips its available resources.

Competition The main density-dependent factor Compete for resources Can be interspecific or intraspecific

Competitive Exclusion Principle Two species cannot occupy the same niche, in the same place, at the same time If there are 2 species with very similar requirements there are 2 outcomes: One species out competes the other Species undergo evolution and therefore occupy different niches.

Factors Influencing Population Growth Nearly all populations will tend to grow exponentially if resources are available. Most populations have the potential to expand at an exponential rate, since reproduction is generally a multiplicative process. Two of the most basic factors that affect the rate of population growth are the birth rate, and the death rate.

Two modes of population growth. The Exponential curve (also known as a J-curve) occurs when there is no limit to population size. The Logistic curve (also known as an S-curve) shows the effect of a limiting factor (in this case the carrying capacity of the environment).

Relationships in Communities between Populations - PREDATION An interaction where an individual of one species (predator) eats all or most of an individual of another species (prey). The most thoroughly studied consumptive relationship between species. Of high ecological and evolutionary significance. An everyday occurrence in nature.

Possible Outcomes of Predation 1. Predator population has little effect on abundance of prey. 2. Predator population eradicates prey population; 3. Predator and prey populations coexist. this may contribute to extinction of predator population due to lack of food.

Prey Population Living Alone Assume a constant rate of increase in absence of predators.

Predator Population Living Alone Assume a constant rate of decline in absence of predators.

A Model Predator/Prey Cycle This graph shows a limit cycle of predators and prey.

The Hare & Lynx Predator/Prey Relationship Snowshoe hare and Canadian lynx show classic population cycles with a 10-11 year cycle. Hare are herbivores and feed on twigs under the snow in winter; lynx feed primarily on snowshoe hare.

The Hare/Lynx Cycle Based on Pelt Sales Similar data is provided in Figure 53.10 (Freeman, 2005).