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Ecological Relationships

A summary explanation of the science of Ecological Relationships.

Date : 23/04/2017

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Thomas

Uploaded by : Thomas
Uploaded on : 23/04/2017
Subject : Biology

Ecological Relationships


A summary explanation of the science of Ecological Relationships.

 

A habitat is any place where organisms live.  Organisms can survive only in habitats which provide them with all the essentials for life and reproduction.  (QCA 2000) The variables which differentiate habitats are known as environmental factors.  These include abundance or lack of water, temperature, access to sunlight, rainfall, shelter from or exposure to wind, quality of soil, drainage and relief. Since a range of habitats offer such variety of environmental factors, each habitat supports a different range of plants and animals.  Individuals more suited to an environment are more likely to survive and reproduce and in doing so pass on the traits that allowed them to thrive.  If this continues over a number of generations, the organism is said to have adapted to its environment.  Groups of organisms which alter sufficiently over many, many generations are said to have evolved into new varieties and new species.  (Darwin 1859, cited in Wikipedia 2009)

 

Organisms are categorised firstly into plants and animals.  Animals are then subcategorised into vertebrates (those with backbones) and invertebrates (without).  Each group is then further subcategorized.  Vertebrates include mammals, reptiles, amphibians, birds and fish.  Invertebrates (98% of the earth’s animal population (Wikipedia (2) 2009)) include arthropods (subcategorised yet further into insects, arachnids and crustaceans), molluscs, worms and jelly-like sea creatures.  Plants too can be subcategorised, including conifers, ferns, mosses and liverworts and flowering plants.  Organisms in each subcategory have characteristic traits in common.  These characteristics can be used to classify organisms.  Each subcategory is further subcategorized and the lower the level of subcategory, the more characteristics the organisms in it will share.

 

Plants and animals are affected by and in turn affect the environmental factors in their habitat.  Populations of different organisms occupying the same or neighbouring habitats also interact with and affect each other.  One of the main ways this takes place is through feeding habits.  Animals eat plants and/or other animals.  Decaying remains of dead plants and animals help to nourish plants.  Food chains are simple diagrams used to show feeding patterns.  Food chains are linked together in food webs.  Arrows indicate the transfer of energy from plants and animals which are eaten to animals doing the eating.  Organisms at the bottom of a food chain are known as producers and those that eat them, primary consumers.  Those that eat primary consumers are called secondary consumers and so on.  Within animal feeding patterns, the terms predator and prey are more commonly used to describe eater and eaten.

 

 

 

Given the web of interactions between different organisms sharing a habitat, it is inevitable that a change in the population of one organism will cause a change in the population of another sharing the same habitat.  For example, in the food web above, if a cold winter killed off much of the grasshopper population it would mean less food for the frog population and a sharp drop in its numbers would be expected to follow which would in turn reduce food for the owls and snakes that prey on the frogs, reducing their number.  A fall in the mouse population however could be expected to cause an increase in the frog population, since the mice and frogs compete for food (grasshoppers). 

 

Pyramids of numbers can be used to represent the size of populations in feeding relationships, with producers on the bottom and consumers layered above.

 

This can, however give a misleading idea of the energy transfers involved:  Pyramids of mass, where the size of a layer depends on the mass, rather than the number of the population are often clearer.

 

 

Measuring population size can reveal important information about the interactions between populations, each other and environment, however, measuring whole populations is often difficult for various reasons – they may be spread over a large area or be dangerous or inaccessible.

 

Sampling is the technique where a small part of a population is measured to represent the whole.  In biology, small areas are often measured (often with a quadrat, a square of known area which should be ‘thrown’ at random to mark out a sample area) and the population recorded therein multiplied by an appropriate scale factor to estimate the whole population.  The more samples are taken, the more likely the estimate to be accurate.  Given the often uneven distribution of populations, location of samples can also affect the representativeness of the samples – for example at edge or middle of a field.

 

Human interaction can affect organisms.  Researchers in the field must be careful to ensure that their activities have a minimal effect on the organisms they are investigating.

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