Population Interactions

Competition

Competition is a part of nature as species compete for food, territory, and mates

Interference competition: direct combat, individuals of one species harm individuals of another species directly.

Exploitative competition: when 2 or more populations use the same limiting resource, so the presence of one species reduces the resource ability for the other.

In the 1920s, a mathematician and a biologist teamed up to experiment the effects of competition between 2 species. They grew 2 different cultures of paramecium separately, and when the placed them together, the one almost completely eliminated the other.

This inspired them to propose a principle, which states that 2 or more species cannot coexist indefinitely if they rely on the same limiting resources.

Fundamental Niche

The fundamental niche of a species is the range of condition and resources that the popluation could possibly tolerate and use

Realized Niche

The range of conditions and resources that a population actually uses in nature. The realized niche is much smaller than the fundamental niche. Biologists can visualize the competition between 2 species by mapping out the niches of each species and if they overlap, the species might compete

Defense mechanisms

Camouflage: organism mimics the pattern of the surrounding environment (e.g. colour changing)

Chemical defense: organism becomes chemically unattractive, it releases noxious odours or concentrates poisonous chemicals in its body (e.g. skunks)

Behavioural defense: passive (hiding, freezing) or active (fleeing, herding, distraction displays)

Mimicry: one species making itself resemble another. Two types, Batesian and Mullerian. Batesian is when a harmless species resembles a dangerous or poisonous species. Mullerian is when two unpalatable species (poisonous) that share common predators look the same.

Spines and Armour: animals and plants with hard, thorny, or needle like structures. (e.g. porcupine)

Population Cycling

Predation: interaction in which the population density of predators increases while the population density of the prey decreases.

Predator population fluctuation follows the prey population fluctuation throughout time.

Population cycles occur when the growth rate of population varies in a recognizable pattern.

Prey density increases when there are fewer predators, the increasing number of predators causes the prey population to decline.

Predator density increases when an abundant amount of prey is captured, density decreases as prey density decreases.

Variables affecting the cycling of population size can include catastrophic natural events, changes in climate, and human interference.

Symbiosis

Symbiosis occurs when one species has a close ecological association with another.

Biologists recognize 3 types of symbiotic relationships, mutualism, commensalism, and parasitism

Mutualism

Both partners in the relationship benefit. An example would be flowers and bees. The bees feed on the plant's nectar and carry the pollen (the plant's gametes) from one flower to another

Commensalism

One species benefits and the other is unaffected. Commensalism is rare in nature because few animals are unaffected by interaction. An example would be cattle egrets (a type of bird) tend to hang around large grazers (like elephants) who flush out small animals and insects from the grass.

Parasitism

One species benefits and the other is harmed. These types of relationships can be seen as predator-prey relationships and parasite-host relationships. An example would be the parasitiod wasp and the aphid. The wasp lays its eggs in the aphid and the aphid lives while the egg is developing. When the larva hatches, it eats the aphid from the inside.

Camouflage: organism mimics the pattern of the surrounding environment (e.g. colour changing)


Spines and Armour: animals and plants with hard, thorny, or needle like structures. (e.g. porcupine)

Chemical defense: organism becomes chemically unattractive, it releases noxious odours or concentrates poisonous chemicals in its body (e.g. skunks)


Behavioural defense: passive (hiding, freezing) or active (fleeing, herding, distraction displays)


Mimicry: one species making itself resemble another. Two types, Batesian and Mullerian. Batesian is when a harmless species resembles a dangerous or poisonous species. Mullerian is when two unpalatable species (poisonous) that share common predators look the same.