Environmental change and species distribution overview
Ecology • Organisation of an ecosystem
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Key concepts
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Definitions and limiting factors
Distribution describes where a species occurs across a habitat or geographic area. Abundance describes how many individuals live in those areas. A limiting factor is any abiotic or biotic condition that restricts survival, growth or reproduction; examples include temperature, water, pH, oxygen availability and food. Limiting factors set the tolerance range for a species and define its realised niche.
Abiotic drivers: temperature, water, pH and gases
Temperature determines physiological processes and sets latitudinal and altitudinal limits for species. Small increases in mean temperature cause poleward or uphill range shifts as organisms track preferred thermal conditions; seasonal temperature changes cause migration in many animals . Water availability controls plant and animal distributions; very low water forces adaptations or exclusion from deserts, while localized water sources (oases) support higher local biodiversity . Soil pH and mineral content determine which plant species establish; pH changes by liming or acid pollution therefore alters plant communities and their consumers . Atmospheric gases and air pollutants change species occurrence; lichens act as bioindicators because many lichens tolerate only low pollution levels .
Biotic drivers: interactions, disease and invasive species
Predation, competition and disease alter population sizes and distribution by changing survival and reproductive rates. Introduction of a new predator or competitor can cause rapid declines or local extinction of native species, and new diseases can decimate populations. Invasive species often outcompete natives because of absent natural predators; the cane toad provides a clear example of an introduced species causing community change .
Human-caused environmental change
Deforestation reduces habitat area and connectivity, lowers local biodiversity and changes local climate and water cycles, which further shifts species distributions and increases extinction risk . Pollution of air and water changes abiotic limits and produces zones where sensitive species disappear; bioindicators reveal these changes through presence/absence patterns . Global warming drives long-term range shifts and may enable disease vectors or tropical species to colonise formerly unsuitable regions .
Responses of species to environmental change
Species respond by moving (migration or range shift), adapting genetically or phenotypically, changing life-cycle timing, or facing local extinction. Movement causes community reassembly and novel species interactions. Adaptation requires sufficient time, genetic variation and population size; rapid environmental change often outpaces adaptive capacity and increases extinction risk .
Evaluation framework for impact on distribution
Evaluation uses cause→effect logic: identify the environmental change, measure direct physiological effects and document distributional responses, then assess secondary effects and long-term outcomes. Reliable evidence includes repeat surveys, indicators (e.g., lichens), controlled experiments and long-term monitoring. Sampling design must avoid bias through random or systematic sampling and adequate sample size to infer real distribution changes .
Key notes
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