How Wildlife Populations are Impacted by Habitat Changes

Habitat changes can take a large number of forms.  The wildlife manager will be mainly concerned with how habitat change will affect wildlife populations.  Changes to habitats will cause changes to food supply, changes to migration patterns and stress in wildlife populations.  These things can have profound effects on wildlife populations.

The type of habitat alteration directly affects the type of influence it has on the wildlife there – whether it be altered breeding cycles, age structure of the population, animal health, etc.  

Physical Changes
Physical changes to habitats include destruction and reduction in habitat.  One thing that many people do not think about is a reduction in the size of habitat due to fragmentation of a natural area.  When a natural area becomes fragmented or even just divided, it can have a big impact on both the vegetation and wildlife in the area.  Vegetation in fragmented areas has weedy edges, and the altered microclimate can cause changes in the vegetation composition.  These changes alone can impact animals.  In small fragments, there may not be enough resources such as food, shelter and nesting sites to support a viable population of animals.  If animals are migratory, fragments can prevent the animals from moving in their traditional way.  Wildlife corridors and road crossings have been experimented with as a way to link fragments and decrease division - but with mixed results.

Biological Changes
All over the world, there are examples of unwanted species – such as possums and deer in New Zealand, foxes and rabbits in Australia, and cats in many other countries.  The introduction of new species into an ecosystem can have profound effects on wildlife.  Introduced species can actually displace native species by taking over their role in the ecosystem; compete with native animals for resources, or simply predate upon native species.

Sometimes, wildlife managers will intentionally introduce an exotic species so that it will have some beneficial impact on the ecosystem.  This is known as biological control.  For example, the North American Screw Worm fly has been a pest in cattle grazing areas in the past.  Scientists introduced sterile male flies into the ecosystem, knowing that the female flies only mate once.  The male flies mated with the female flies, who then did not reproduce – thus the population dropped dramatically.  Introducing individuals from outside can actually have a beneficial effect on the ecosystem.

Air Pollution

Air pollution can have long and short term effects on wildlife habitats.  It varies somewhat depending on the locality of the wildlife.  One particularly pertinent example of air pollution is acid rain.  This can have a devastating effect on the food source and nesting areas of wildlife.

Water Pollution
Water pollution affects both aquatic and land based wildlife.  When water is overused by mankind, it can lead to changes to the water table.  This can have long term flow on effects such as salinity and topographical changes.

Changes in water chemistry due to runoff, sewage disposal, industrial waste, etc can all have dramatic effects on wildlife habitats and populations.  A wildlife manager must be aware of the importance of clean water in the habitat.

Toxic Chemicals
When toxic chemicals come into an ecosystem, they can affect animal opulations. Often with only mild levels of pollution, only one or two species may be impacted; but as the populations of those species decline; their absence can then have a flow on affect upon populations of other species that may feed on them; or be impacted by them is some other way.

Water Loss
Water is a very important resource, and whether managing a small or large area, managers need to be aware of how water affects animals in a terrestrial situation.

Some reserves may be huge, but ensuring a water supply at all times over several years may be difficult.  The fact that wildlife habitats are now fragmented means that wildlife can be restricted in where they can move to in order to find water.  Some birds may have a wider range than non flying animals.  However, there is still only a certain distance that any one animal can travel in order to reach water.  When assessing the water supply in a wildlife habitat, the following should be taken into account:

  • Area of habitat
  • Carrying capacity (see later lessons)
  • List of species present
  • Daily water requirements of each wildlife species being managed
  • Previous rainfall and evaporation data for the area
  • Contour maps of the area so that the stream flow catchments can be anticipated
  • Recent aerial photographs can be useful to indicate the condition of the existing vegetation
  • Vegetation and soil maps
  • Information about other activities that require water in the area – for example agricultural irrigation schemes, human settlements, etc.

If you have the above information, you can plan ahead to provide water to wildlife in an appropriate manner.