ECOLOGICAL APPROACH
■ The study of animals and plants in relation to their habits and habitation
(habitat) is ecology. Ecology developed as a discipline relating to animals and plants, but has been extended to include microorganisms and has a qualitative and quantitative framework similar to epidemiology
■ Ecosystem: The relationship between animals linked by food chains defines the variety of animals in a particular area. Three types of ecosystem can be
identified, according to their origin:
– Autochthonous ecosystems: is one ‘coming from the land itself – Anthropurgic ecosystems: is one created by man
– Synanthropic ecosystems: is one that is in contact with man.
Synanthropic ecosystems facilitate the transmission of zoonotic infections from their lower animal hosts to humans
ECOLOGICAL APPROACH-2
■ Biotope: is the smallest spatial unit providing uniform conditions for life.
An organism’s biotope therefore describes its location.
– A biotope can vary in size. For example, it may be the caeca of a chicken for coccidia
■ Biocenosis (biotic community): is the collection of living organisms in a biotope. The organisms include plants, animals and microorganisms in the biotope.
– Sometimes biotic community is used synonymously with biocenosis.
On other occasions, biotic community refers to a large biocenosis.
– Major biotic communities are biomes
ECOLOGICAL APPROACH-3
■ Biomes: It has large plant and animal structure and large areas
determined by climatic conditions. Tropical rain forest, savannah and tundra are biomes, each with its own particular range of plants and animals
■ Ecological climax: Traditionally is said to have occurred when plants, animals, microbes, soil and macroclimate have evolved to a stable,
balanced relationship, and originally was used in relation only to plants
■ Ecological niche: It is the place or functional position of an organism in a community.
■ Ecological interfaces: The factor that separates the two ecosystems
from each other, or the link between the two ecosystems.
ECOLOGICAL APPROACH-4
■ Ecological mosaics: is a modified patch of vegetation, created by
humans, within a biome that has reached a climax. Infection may
spread from wild animals to humans in such circumstances
REGULATION OF POPULATION SIZE
■ The ‘balance of nature’: Populations grow, reach a certain size, and then stop growing. The population becomes stable and balanced, with the rate of
reproduction equalling the death rate
– The currently accepted theory is that populations are brought into balance by competition for the resources of the habitat, the most common of which is food. Competition therefore is density dependent.
■ Predation: has an obvious plausible role in controlling the size of populations but, in large animals, there is contradictory evidence
■ Epidemiological interference: The settlement of other living organisms in an ecological niche which is occupied by a living organisms
Reference: Veterinary Epidemiology, 4ed. Michael Thrusfield with Robert Christley, Brown H, Diggle PJ, French N, Howe K, Kelly L, O’Connor A, Sargeant J, Wood H.
