Environmental Change Impact

When an environmental condition changes, a previously suitable place may become unsuitable. Meanwhile, another place may become suitable. Mobile animals may move, migrate or expand into the newly suitable area. Plants cannot move as individuals, but their distribution can shift over generations when seeds disperse and establish in new places. If a species cannot move or adapt quickly enough, its local population may decline or disappear.

Temperature changes

Organisms are adapted to function within a particular range of temperatures. Temperature affects enzyme-controlled reactions and therefore processes such as respiration, growth and reproduction. Beyond a species’ tolerated range, it may grow or reproduce less successfully, or fail to survive.

Temperature changes can therefore alter the boundaries of a species’ range. As average temperatures rise, some European plant, bird and insect species have spread northwards into areas that were previously too cold. At the same time, warmer conditions can make parts of their former range less suitable. This is not simply “all species move north”: the direction and size of any shift depend on the species, local geography and its ability to disperse.

Seasonal temperature changes can also produce temporary changes in distribution. For example, animals may migrate between breeding and feeding areas, while seasonal plant growth changes where food and shelter are available.

Changes in water availability

Water is needed for reactions inside cells. Plants also require it for photosynthesis, transport and maintaining their tissues. Water availability therefore has both direct and indirect effects: an animal may need drinking water, but it may also depend on water for its habitat or for the plants at the base of its food web.

During a drought, organisms may move towards rivers, pools or wetter ground. Those unable to move may experience reduced survival or reproduction. Regular seasonal rainfall can produce repeating movements: wildebeest migrations in Africa follow rainfall because it supplies water and promotes fresh grazing. Longer-term changes in rainfall may shift the area in which a species can persist.

Changes in atmospheric gases

Changing the composition of the air can affect organisms because gases are used in biological processes or may act as pollutants.

Oxygen is required for aerobic respiration, while carbon dioxide is required for photosynthesis. A change in carbon dioxide concentration can therefore affect plant growth, although the outcome in a real ecosystem may also be limited by temperature, water, light or mineral ions.

Some species are particularly sensitive to gaseous pollutants. For example, some lichens cannot grow where sulfur dioxide is present. Their absence from polluted areas and presence in cleaner areas produces a change in distribution. However, different lichen species have different tolerances, so evidence should be interpreted for the particular species identified rather than for “lichen” as a single group.

Seasonal, geographical and human-caused change

Environmental change can occur in several overlapping ways:

• Seasonal: temperature and rainfall vary through the year, potentially causing migration, dormancy or seasonal growth.
• Geographical: conditions differ between locations—for example, temperature may fall with increasing altitude or latitude.
• Human-caused: greenhouse-gas emissions can alter climate, while industrial emissions can change local air quality.

These categories describe the origin or pattern of a change, not three separate biological mechanisms. A human-caused change in climate can, for example, alter both geographical temperature patterns and seasonal rainfall.

Evaluating evidence

To evaluate an environmental change, first identify the environmental factor and the measured biological response. Then describe the pattern accurately: state where the species becomes more or less common, appears or disappears, or how the boundary of its range changes. Use figures and units from any supplied graph or table.

Next, explain a plausible mechanism connecting the factor to survival or reproduction. For example:

less rainfall → less plant growth and less surface water → reduced food and drinking water → animals leave or fewer survive → distribution changes

Finally, judge how confidently the data support that explanation. If plant species richness falls as altitude increases and temperature falls, the results show a correlation. They do not prove that temperature is the cause, because moisture, soil, wind and light may also change with altitude. Repeated sampling, measurements of other variables and evidence from several locations would strengthen the conclusion.

A sound evaluation also distinguishes distribution from abundance. Finding fewer individuals at one sampled site might indicate a range shift, but it could instead be a local fall in population size or imperfect sampling. The best conclusion is one that matches the evidence without claiming more than the data show.