Ecology

Patterns in the Environment Where an organism lives is called it’s Habitat. It is shaped by the organisms interaction with abiotic and biotic factors.

habitats

Niche An organisms niche is its functional position in the environment. It includes a description of how the organism interacts with the abiotic and biotic elements of the environment.

Niche

The law of tolerance states that “For each abiotic factor, an organism has a range of tolerances within which it can survive.” Law of Tolerance- abiotic factors Examples of abiotic factors that influence size of the realized niche: Tolerance range Optimum range Unavailable niche Marginal niche Number of organisms Preferred niche Marginal niche Unavailable niche

Competition affects the size of a competitor’s realized niche. The effect is dependent on the intensity and type of the competition. Niches are narrower with moderate interspecific competition (Fig. 1). Intense interspecific competition results in a very narrow realized niche as species specialize to exploit a narrower range of resources (Fig. 2). Intense intraspecific competition results in a broader realized niche as individuals are forced to occupy suboptimal conditions (Fig. 3). Biotic factors -Competition and Niche Size Fig. 1 Fig. 2 Fig. 3 Narrower niche Broader niche Possible tolerance range Realized niche of species

Gause’s competitive exclusion principle states: “two or more resource-limited species, having identical patterns of resource use, cannot coexist in a stable environment: one species will be better adapted and will out- compete or otherwise eliminate the other(s)”. If two species compete for some of the same resources (e.g. food items of a particular size), their resource use curves will overlap. In the zone of overlap, interspecific competition is the most intense. Gause’s Principle Zone of overlap Species B Resource use as measured by food item size Amount eaten Species A

Competing species cannot occupy the same niche

Barnacles Chthamalus and Balanus compete for space. Note that Chthamalus realised niche is much smaller than its fundamental niche as it is out competed by Balanus.

Interspecific competition is usually less intense than intraspecific competition because niche overlap between species is not complete. Species with similar ecological requirements may reduce competition by exploiting different microhabitats within the ecosystem. Example: Ecologically similar damsel fish at Heron Island, Queensland, Australia exploit different resources or regions over the coral reef. Niche Differentiation Sea levelReef crest PwPomacentrus wardi PfPomacentrus flavicauda PbPomacentrus bankanensis SaStegastes apicalis PlPlectroglyphidodon lacrymatus EfEupomacentrus fasciolatus EgEupomacentrus gascoynei GbGlyphidodontops biocellatus

Zonation in a lake

Zonation- changing environments are often divided into zones

Stratification in a forest is a type of vertical zonation

Different organisms will occupy different niches within the different zones

Succession Communities change over time. Early communities alter the environment allowing other organisms to colonise. Eventually a climax community will form

Secondary succession occurs after a catastrophe or something that disrupts the environment

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