Interactions between plants and animals

Plants live together with animals in communities (biocenoses) and influence each other. Plants offer animals nutrition and they offer certain structures (e.g. nesting sites and mating areas) and are a framework for information (e.g. meeting places and nutrient availability). Animals influence plant life not only by herbivory and by modifying the site (e.g. soil burrowers and termites), but particularly in their roles as pollinators and dispersers. Here, there are countless mutual interactions. Birds and butterflies are pollinators during the day as they are attracted via the colours of flowers or availability of nectar and pollen, where as bats are active at night and are attracted by smell, e.g. of ripe fruit. Synchronised interactions are often very specialised in time and location, and are considered to result from co-evolution.

A large influence is herbivory: distinction is drawn between grazers which mainly eat herbs and grasses in pastures, and browsers which also eat woody species, often including roots. In natural ecosystems generally only a small proportion of the available standing biomass is used. Plants have developed chemical and physical defence mechanisms and respond with compensatory growth, overcoming excessive herbivory.

The relationship between plants and animals at the level of communities is considered in the biocenology. Here the principle of a biocenotic equilibrium is recognised, and countless rules describing community organisation in biocenoses have been formulated. A particularly rich area is research into functional interactions between single organisms and their environment.

I Table 4.3.4. Potential interactions between two organisms

Type of interaction

Organism 1 Organism 2 Type of interaction

Symbiosis (mutalism and protocooperation) + Commensalism (parabiosis, epecology, e.g. + epiphytes, epizoics, metabiosis) Parasitism (antibiosis, allelopathy and antag- + onism)

Neutralism o

Amensalism

Competition

Interaction beneficial to both organisms Interaction beneficial to one organism, without disadvantaging the other Interaction benefits one organism to the detriment of the other Interaction without a beneficial or detrimental effect

Interaction leads to a detrimental influence on one organism without aiding the other Interaction leads to mutual disadvantage o, neutral influence; +, positive, advantageous influence; -, negative, disadvantageous influence

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