Biotic and Abiotic Interactions

Biotic and Abiotic Interactions

•Abiotic - Non living factors

–Temperature

–Light intensity

–Soil pH

–Availability of water

–Availability of minerals

•Biotic – living factors

–Competition

–Predation

–disease

Density dependent and density independent factors

•Density dependent factors

–Effect increases of population density increases

–Population level off, then decrease

–Example - availability of food

•Density independent factors

–Effect independent of the size of the population

–Example – forest fire

Biotic Interactions

•Interspecific interactions

–Between individuals of different species

•Intraspecific interactions

–Between individuals of the same species

Biotic Interactions

•Predation

•Grazing

•competition

Predation

•Patterns of predator prey interaction

–Stable coexistence

–Cyclical variations

–Erratic swings

–Extinction of prey species

•Important factors to consider

–Carrying capacity of the habitat

–Reproduction rate of prey

–Reproduction rate of predator

–Degree of flexibility of predator to switch prey

Role of Predators in maintaining diversity

•By removing prey who are strong competitors, weaker competitors can survive

•Reduce effect of competitive exclusion

•The ecosystem benefits from

–Increasing species diversity

–Increasing stability

–The ability to adapt to environmental change

•Examples where removing predators has collapsed an ecosystem

–Otters and the sea kelp forests

Prey defenses to predators

•Camouflage

•Warning (aposematic)colouration

–Red, black and yellow are aposematic colours

•Mimicry,

•Batesian,

•Mullerian

Grazing

•A grazer is defined as

–Any species that moves from one victim to another, feeding on part of each victim without actually killing it outright

•E.g. eating a shoot or a limb

•Can increase or decrease species diversity depending on grazing pressure.

Grazing of Vegetation

•Plant species with basal meristems can be grazed without suffering mortality

•Plant species with aerial meristems can be eliminated by grazing when the aerial part is removed.

•Grassland is often referred to as a plagioclimax, where a diversion deflected succession off course to reach the natural climax community e.g. fire, grazing, mowing

Competition

•Exploitation competition

–Consumer significantly reduces the resource

•Interference competition

–One species prevents individuals from another from using a resource

•Competitive interactions can:

–Short term – variations in abundance and distribution

–Long term – evolutionary adaptations to improve competitive ability

Styles” of Competition

•Exploitation competition

–occurs when individuals use the same limiting resource or resources, thus depleting the amount available to others.

•Interference competition

–occurs when individuals interfere with the foraging, survival, or reproduction of others

–directly prevent their physical establishment in a portion of a habitat.

Niche

•The sum of

–An organism’s adaptations

–The resources it needs

–The lifestyle to which it is fitted

•Gause’s principle of competitive exclusion

–When cultured together Paramecium aureliahas a competitive advantage over P. caudatum for gaining food.

– Fundamental niche

–Realised niche

Introduction of “exotic species”

•Rhododendron ponticum - Scotland

–Dense canopy

–Leaves contain toxins

•Nile Perch – Lake Victoria

–Carnivourous fish eating species

•Rabbits and Prickly Pear cactus – Australia

•Hedgehogs – Outer Hebrides

•Rats – New Zealand

Importance of survival of weaker species

•Species diversity is essential

•If environmental conditions change,

–The dominant species may no longer be the best adapted and die out

–This gives the weaker competitors who are better adapted a chance to increase in number

•E.g. extinction of the dinosaur and the emergence of mammals