Module 2.2: Species Interactions, Ecological Succession, and Population Control

Prelim topic

Interspecific Competition

(Species Interaction)

• The most common type of interaction:

• When 2 species compete for the same resource, their niches overlap

Resource Partitioning

• Occurs when competing species evolve specialized traits that allow them to use shared resources at different times, in different ways, or in different places

Predation

(Species Interaction)

• When an individual of one species feeds directly on another plant or animal species

• The two species are engaged in a predator-prey relationship

• This has a strong effect on population size and other factors

Coevolution

• Happens when populations of 2 different species interact over a long period of time, changes in the gene pool of one species can lead to changes in the gene pool of the other

Parasitism

(Species Interaction)

• This occurs when one species feeds on the body of, or the energy used by another organism (host) - usually by living on or in the host

• They are usually much smaller than its host and rarely kills it

• Tapeworms live inside the host, mistletoes and sea lampreys attached themselves outside of the host

Mutualism

(Species Interaction)

• This occurs when 2 species behave in ways that benefits both

• Providing each with food, shelter, protection, or some other resources

• Ex: Birds ride on the backs of large animals and remove pests (African Buffalo), Bacteria that live in our intestines and help us digest food

Commensalism

(Species Interaction)

• This occurs when one species benefits from species interaction, and the other is not affected or harmed at all

• Ex: Air plants known as epiphytes attach themselves to the trunks or branches of large trees to access sunlight

Ecological Succession

• The normal, gradual change in species composition in a given geographic area

• The species composition of an ecosystem or community can change in response to changing environmental conditions

• Primary and Secondary succession

Primary Succession

(Ecological Succession)

• The gradual establishment of biotic communities in lifeless areas where there is no soil in a terrestrial ecosystem or no bottom sediment in an aquatic system

• Takes hundreds to thousands of years

Secondary Succession

(Ecological Succession)

• Occurs when communities or ecosystems have been disturbed, removed or destroyed, but retain some soil or bottom sediments

• Enriches biodiversity of communities and ecosystems by increasing species diversity and interaction among species

• Promotes population control: increase complexity of food webs, enhances energy flow, increases nutrient cycling

Tolerance

• A population and its ability to survive under various physical and chemical environmental conditions

• Some individuals in a population may also have different ranges of tolerance for temperature or other physical or chemical factors - known as limiting factors

Density

• The number of individuals in a given geographic area

J-Curves

• Some species reproduce and grow rapidly: plotting this data generates this curve showing exponential growth.
  - Members reproduce at an early age; many offspring in each generation; time between generations is short

Environmental Resistance

• The sum of all factors that limit the growth of a population

Carrying Capacity

• The maximum population of a given species that a habitat can sustain indefinitely

• As the population approaches its carrying capacity, its J-curve becomes an S-curve of fluctuating logistic growth

Population Crash

• When a population overshoots the carrying capacity, the population sharply declines

• Now a population must either: stabilize its population, switch to new resources, or move to a new geographic area

r-selected species

(Species Reproductive Patterns)

• These species have a capacity for high rate of population increase

• They have short life spans

• Have many, usually small offspring

• Do not provide much parental care/protection
  - Offspring loss is overcome by massive offspring production, so that at least a few will survive

Oppurtunists

(Species Reproductive Patterns)

• These species reproduce rapidly under favorable environmental conditions

• Often occurs after a fire or clearing an area that opens up new habitats or niches for invasion of a new species

• May crash after growth or when yet another species invades the area

• Go through irregular and unstable boom-and-bust cycles

k-selected species

(Species Reproductive Patterns)

• These species do well in competitive conditions when population size nears carrying capacity

• The reproduce later in life

• Have smaller numbers of offspring with longer life spans

• Typically develop inside their mothers and are born fairly large

• After birth, they mature slowly and are protected by one or both parents