Scales of Ecological Organization

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

Population – group of individuals of the same species living in the same area, potentially interacting Community – group of populations of different species living in the same area, potentially interacting What are some ecological interactions?

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.

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.

The size of a population depends on the rates of birth, death, immigration and emigration r = (b+i) – (d-e) Factors that influence population growth as the numbers increase are called DENSITY DEPENDENT eg food supply Birth rates and death rates may vary regardless of population density. Factors which make this happen are called DENSITY – INDEPENDENT eg environmental changes

Types of ecological interactions competition predation parasitism mutualism commensalism symbiosis

Competition – two species share a requirement for a limited resource  reduces fitness of one or both species

Predation – one species feeds on another  enhances fitness of predator but reduces fitness of prey herbivory is a form of predation

Parasitism – one species feeds on another  enhances fitness of parasite but reduces fitness of host

Mutualism – two species provide resources or services to each other  enhances fitness of both species

Commensalism – one species receives a benefit from another species  enhances fitness of one species; no effect on fitness of the other species

Symbiosis – two species live together  can include parasitism, mutualism, and commensalism

Organizing ecological interactions effect on species 1 + 0 - predation herbivory parasitism + - commensalism mutualism effect on species 2 competition

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.

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).

Interaction between Populations can influence population numbers- 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).

Human Population Has been 3 population explosions 20 000yrs ago due to tools 6000yrs ago increase in farming 300yrs ago improvement in medicine etc Humans unlike other species populations have created environmental changes to raise the normal population carrying ability To what extent can the human species can continue to change the environment to sustain an ever increasing population?