Homeostasis and Negative Feedback in Ecosystems

A key feature of ecosystems is homeostasis – the ability to maintain stability and balance in the face of external changes or stresses through self-regulation. Negative feedback loops are a key mechanism behind achieving homeostasis.

Negative Feedback

In a negative feedback loop, a stimulus or change triggers a response that counteracts or reduces the original stimulus, keeping conditions within an acceptable range. The variable that’s being regulated is known as the controlled variable while the stimulus that causes a change is called the input signal.

We can understand it by animal body example of Negative Feedback. In mammals including humans, the body temperature is the controlled variable. If it starts rising too high, sensors detect this change (the input signal) and initiate responses like sweating or blood vessel dilation to cool the body, reducing the elevated temperature (the counteracting response). Once temperature is back in the normal range, these cooling responses are reduced or switched off.

Now, let’s take an ecosystem example. In grassland ecosystems, soil moisture is an important controlled variable. Many factors can alter soil moisture, acting as input signals to the system. For instance, reduced rainfall would act as an input signal, lowering soil moisture. This drying triggers counteracting responses from the grassland plants and ecosystem – grasses may slow their growth rate or go dormant to reduce water loss, leaf surfaces may close stomata preventing evapotranspiration losses, and root systems may extend deeper tapping water tables. These responses all serve to conserve soil moisture.

Once rainfall picks up again and soil moisture is restored to prior levels, the water-conserving responses of the grasses and ecosystem would slow down or reverse. Growth rates may increase again, stomata reopen and deep root growth decreases. This demonstrates a self-regulating, negative feedback loop where the ecosystem’s response works against the original input stimulus of declining moisture to keep soil water in a suitable range. Similar negative feedback mechanisms maintain stability in other ecological variables like fire regimes, predator-prey populations and nutrient cycles.

Types of Ecosystem Homeostasis

Ecosystem homeostasis occurs at both the individual organism level as well as higher community and system levels through key processes:

Organism-Level Homeostasis

Organisms maintain internal stability of variables like body temperature, fluid balances, respiration and metabolism in the face of external fluctuations. This is achieved through negative feedback via nerve responses, chemical signaling like hormones, enzyme regulation, etc. For example, plants can open and close their stomata to maintain internal CO2 levels for photosynthesis.

Population Homeostasis

Populations self-regulate their sizes through availability of food, competition for resources, predation, disease and reproductive capacity, allowing long term stability. For example, as more coyotes enter an area, they may exhaust prey resources, leading many to starve or migrate away until the population stabilizes at the carrying capacity.

Community Equilibrium

Species interactions and natural selection guide community evolution toward an equilibrium where various niches are optimally filled. For example, grass production may be kept stable by herbivore grazing pressures and nutrient cycling. If grasses are grazed too much, herd sizes fall reducing grazing pressure and allowing regrowth.

Resilience Ecosystem Homeostasis

Ecosystems have built in buffers, feedback loops and pathways that confer resilience against external perturbations and rapid changes. For example forest soil microbes, fungi and invertebrates form complex food webs that allow nutrient recycling and decomposition processes to continue at functional rates even if individual species are lost.