Effects of environmental change on communities
Ecology • Adaptations, interdependence and competition
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Definitions and limiting factors
Abiotic factors are the non-living parts of the environment that affect organisms, for example light intensity, temperature, water availability, soil pH and dissolved oxygen. A limiting factor is any abiotic condition that restricts the rate of a biological process or the size of a population, such as light limiting photosynthesis or low dissolved oxygen limiting aquatic animal abundance . Population size responds to the most limiting factor at that time. Multiple limiting factors can interact so that altering one factor can change which factor becomes limiting. Farmers and growers manipulate limiting factors (light, temperature, CO2) to maximise crop yield because growth depends on the most restrictive condition .
Effects of reduced or increased light
Reduced light intensity reduces the rate of photosynthesis in producers, causing slower growth and lower plant biomass. Lower plant biomass reduces food available for herbivores, which reduces herbivore population sizes and then predator populations after a lag phase, producing a cascade of decreasing numbers through the food web . Increased light in an area that previously receives little light (for example a gap in a forest canopy) increases photosynthesis and growth for shade-sensitive plants, enabling opportunistic species to increase faster and outcompete others for space and resources. The community composition shifts as light-demanding species become more abundant .
Effects of temperature change
Temperature affects metabolic rates, enzyme activity and reproduction. A rise in temperature can increase growth and reproduction up to an optimum, beyond which enzymes denature and survival drops; a fall in temperature can reduce metabolic activity and cause mortality in species not adapted to the cold. Species shift their distributions toward areas with suitable temperatures when local climate changes, altering community composition and species interactions fileciteturn0file9turn0file18. Global or local temperature change causes migration of species toward suitable climates and changes in the timing of life-cycle events (phenology). Such shifts alter predator–prey timing and competition, creating mismatches in food availability for dependent species and reducing ecosystem stability .
Effects of changes in pH and soil nutrients
Soil pH and mineral content determine nutrient availability for plants. Acidification or alkalinisation of soil favours some species and excludes others; for example, some plants require acidic soils while others need more alkaline conditions. Altering pH therefore changes which plant species dominate and changes the food and habitat available for animals that depend on those plants . Adding nutrients (fertilisers, manure) increases plant growth but can favour fast-growing species and reduce biodiversity. Excess nutrients can also alter soil pH and produce knock-on effects in the community. Aquatic nutrient increases cause algal blooms that reduce oxygen levels and harm aquatic animals by causing mass mortality events through oxygen depletion fileciteturn0file5turn0file7.
Effects of altered dissolved gases and water availability
Dissolved oxygen in water and atmospheric CO2 influence aquatic and terrestrial producers and consumers. Higher dissolved oxygen supports greater abundance of aquatic animals; lower dissolved oxygen reduces animal abundance and can cause local die-offs. CO2 concentration influences photosynthesis rates; increased CO2 can boost plant growth where other factors are not limiting, shifting competitive balances among plant species fileciteturn0file5turn0file9. Water availability acts as a limiting factor for plants. Increased drought reduces plant survival and food supply, lowering herbivore numbers and then predator numbers. Increased water availability in dry habitats can allow colonisation by new species and change community structure over time .
Effects of changes in biotic factors: food, predators and disease
Reduced food availability directly decreases population size by limiting growth and reproduction. Predator removal increases prey population size until another factor becomes limiting, while introduction of a new predator reduces prey numbers and can cause cascading effects across the food web. Predator–prey relationships often produce population cycles: increases in prey lead to later increases in predators, followed by prey declines and subsequent predator declines fileciteturn0file14turn0file6. Introduced species and new pathogens disrupt communities by outcompeting or killing native species. Invasive species can reduce native populations by competition or predation, and introduced pathogens can cause rapid population crashes. Historical examples include deliberate biological controls or accidental introductions that cause long-term community restructuring .
Interdependence and knock-on effects
Species in a community depend on each other for food, shelter and ecological services. A change to one species or factor often produces indirect effects that are difficult to predict: removing a top predator can increase prey, which can overgraze producers and reduce habitat quality for other species. Such interdependence maintains community stability but also makes communities vulnerable to disruption . Sampling and careful observation provide evidence for distribution changes as environments change. Ecologists use sampling to estimate abundance and distribution and assess how environmental changes shift community composition over time .
Human-driven environmental change
Human activities, such as deforestation, pollution and greenhouse gas emissions, change abiotic and biotic conditions. Climate warming causes habitat loss for cold-adapted species, sea-level rise and changes in rainfall patterns, driving species migration and threats to food security. Local habitat destruction reduces biodiversity and ecosystem stability fileciteturn0file18turn0file19. Management actions alter communities by changing limiting factors or biotic interactions. Restoration, conservation or agricultural practices intentionally change factors such as nutrient levels or predator presence, producing predictable effects when based on ecological principles; unintended side effects occur when interdependence is underestimated fileciteturn0file9turn0file19.
Key notes
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