Population Dynamics and Interspecific Relationships c4.1

Population

Interacting groups of organisms of the same species living in an area

Natality

Increases population size through reproduction (births)

Immigration

Increases population size from external populations

Mortality

Decreases population size as a result of death

Emigration

Decreases population size due to loss to external populations

Population Size Equation

Population Size = (Immigration + Natality) - (Mortality + Emigration)

Population Sampling

Identifying individual numbers in small areas and extrapolating to estimate population totals

Quadrat Sampling

Using a rectangular frame to establish population densities, suitable for non-motile species

Capture-Mark-Release-Recapture

Method to estimate population size of motile species by marking and recapturing individuals

Lincoln Index

Formula: Estimated Population = (n1 × n2) ÷ n3, used in capture-mark-release-recapture method

Limiting Factors

Environmental conditions controlling the rate of population growth

Density-Dependent Factors

Environmental factors influenced by the relative size of a population

Density-Independent Factors

Environmental factors not influenced by the relative size of a population

Negative Feedback

Return of a system to its original state, controlling population size by density-dependent factors

Exponential growth pattern (J curve)

Occurs in an ideal, unlimited environment with no competition initially, resulting in a J-shaped curve

Logistic growth pattern (S curve)

Occurs when environmental pressures slow the rate of growth as population approaches a finite carrying capacity, resulting in an S-shaped curve

Biotic potential

The maximal growth rate for a given population in an ideal environment with unlimited resources

Carrying capacity

The maximum number of a species that can be sustainably supported by the environment

Population clocks

Provide current projections of estimated populations based on recorded data, often using assumed rates of change

Sigmoidal growth curve

Demonstrated by stable populations in a fixed geographic space, following three key stages: exponential growth, transitional phase, and plateau phase

Intraspecific competition

Competition within the same species for resources, often the strongest type of competition

Cooperation in intraspecific relationships

Complex behaviors developed to minimize the impact of direct competition within a species

Community

Consists of all living things in an ecosystem, including all populations of all species

Herbivory

The act of eating only plant matter; can be harmful or beneficial to plant species as a whole.

Predation

Biological interaction where one organism (predator) hunts and feeds on another organism (prey), affecting population levels.

Pathogenicity

Capacity of a microbe to cause damage in a host resulting in disease, impacting population carrying capacity.

Symbiosis

Close and persistent interaction between two species, which can be obligate or facultative.

Mutualism

Ongoing interaction between two species where both benefit from the interaction.

Mucivores

Herbivores that feed on plant sap.

Granivores

Herbivores that feed on seeds.

Folivores

Beetles that feed voraciously on leaves/foliage, causing crop failure.

Frugivores

Fruit-eating animals that spread seeds through their feces, promoting seed dispersal.

Commensalism

Symbiotic relationship where one species benefits while the other is unaffected.

Anemone

Protects clownfish in a mutualistic relationship.

Clownfish

Provides fecal matter for food in a mutualistic relationship with anemone.

Barnacles

Transported to plankton-rich waters by whales in a commensalistic relationship.

Ticks

Parasites that feed on the blood of their canine host.

Chytridiomycosis

Amphibian disease caused by the fungus Batrachochytrium dendrobatidis.

Rhizobium

Bacteria that fixes atmospheric nitrogen in exchange for carbohydrates in a mutualistic relationship with plants.

Mycorrhiza

Fungi that grows in association with orchid roots, supplying nutrients and water in exchange for carbohydrates.

Plover birds

Clean crocodile teeth by picking food morsels from between their jaws in a mutualistic relationship.

Honey bees

Gather nectar from flowers and distribute pollen between plants, mediating plant life cycle in a mutualistic relationship.

Fabaceae

Legume family of plants that form mutualistic relationships with nitrogen-fixing bacteria.

Zooxanthellae

Algae that photosynthesize within the protective environment of the polyp's endodermis, feeding the coral.

Competition

Describes the interaction between two organisms where the fitness of one is lowered by the presence of the other. It can be intraspecific (within the same species) or interspecific (between different species).

Competitive exclusion

One species uses resources more efficiently, driving the other species to local extinction.

Resource partitioning

Both species alter their use of the environment to divide resources between them.

Endemic species

Native to a defined geographic region, e.g., koalas in Australia.

Alien species

Species transferred from their natural habitat to a new environment. If they have a detrimental effect on pre-existing food chains, they are classified as invasive.

Invasive species

Threaten biodiversity by displacing native species in the ecosystem they are introduced into.

Competitive exclusion principle

States that two species cannot occupy identical niches within a community, leading to one species having a competitive advantage over the other.

Fundamental niche

The entire range of conditions an organism can tolerate and resources it can use.

Cane Toads

Introduced in Australia in 1935 to control the sugar cane beetle population, now classified as an invasive species endangering native wildlife.

Wild Rabbits

European rabbits introduced to Australia, causing devastating effects on native ecology due to rapid population growth and destructive feeding habits.

Rabbit-proof fences

Built to contain rabbit populations in an attempt to control their spread.

Myxomatosis virus

A rabbit-borne disease released to control rabbit populations with moderate success.

Tests for interspecific competition

Indicated but not proven if one species is more successful in the absence of another. Various approaches include laboratory experiments, field observations, and manipulation by species removal.

Positive Association

When two species are typically found within the same habitat, indicating a relationship such as predator-prey or symbiosis.

Negative Association

When two species tend not to occur within the same habitat due to competition for the same resources, leading to competitive exclusion or resource partitioning.

Independent Distribution

When two species do not interact, resulting in no association between them and their distribution being independent of one another.

Chi-Squared Test

A statistical test applied to data from quadrat sampling to determine if there is a significant association between the distribution of two species.

Degree of Freedom

A mathematical restriction calculated from the table of frequencies, often 1 when comparing distribution patterns of two species.

Limiting Factor

An environmental condition that controls the rate at which a process, such as population growth, can occur.

Top Down Control

Pressures from higher trophic levels that control population dynamics by suppressing prey abundance or limiting population growth.

Bottom Up Control

Pressures that limit resource availability to lower trophic levels, affecting population growth at higher levels by restricting energy supply.

Allelopathy

Chemical inhibition of one organism by another through the release of chemicals that act as growth inhibitors.

Antibiotics

Chemicals produced by organisms, such as fungi, to kill or inhibit the growth of bacteria, often used as medicines.