Ecological Resilience
Ecological resilience refers to the capacity of an ecosystem to absorb disturbances—whether natural or human-made—while maintaining its essential functions and structure. This concept involves the idea of stable states, where an ecosystem ideally exists in equilibrium without external pressures. However, ecosystems inevitably face some level of environmental stress, making complete stability unachievable. Resilience can manifest either through resistance to disturbances or through adaptation, with varying degrees of resilience evident across different ecosystems. For instance, a grassland may transition into a forest under environmental pressures, indicating a low level of resilience if significant changes occur with limited stress.
The notion of ecological resilience is critical for understanding the health of social-ecological systems, where human activities intersect with natural environments. It has implications for addressing issues like climate change, pollution, and sustainable development. A resilient ecosystem is typically characterized by high biodiversity, allowing multiple species to fulfill similar ecological roles, which enhances stability. Studying ecological resilience helps scientists devise strategies for restoring and managing ecosystems, ensuring they can withstand future challenges while maintaining their functionality and health.
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Ecological Resilience
Ecological resilience is a term used to describe the ability of an ecosystem to respond to changes created by natural or human-made disturbances without losing its original function and structure. Ecosystems may demonstrate resilience either through resistance to stressors or by adapting to these stressors. Ecological resilience is used as a measurement of the relative stability of an ecosystem.
The term relates to what is deemed the "stable state" of an ecosystem. A stable state is the natural state of an ecosystem if no external pressures are applied—that is, it exists in a state of equilibrium. An ecosystem in a completely stable state will continue to function in the exact same way over time. However, all ecosystems experience some level of environmental pressure—whether from natural or human-made disturbances—so maintaining a completely stable state indefinitely is impossible. Examples of ecosystems in a relatively stable state might include grasslands, coral reefs, or degraded lakes. Resilience measures how much disturbance is required to alter an ecosystem so it moves from one stable state to another. For instance, each individual ecosystem may have several natural stable states. In the case of a grassland, environmental pressures may cause this ecosystem to eventually transition into a forest over time. In this example, the ecosystem evolved from one stable state—a grassland—to another stable state—a forest. Therefore, the original grassland demonstrated a low level of ecological resilience because it transformed into a new ecosystem with only limited pressure, albeit over a long period.
A stable or highly resilient ecosystem is not necessarily positive. Biologists cite the example of a eutrophic body of water as a stable but potentially unhealthy ecosystem. Eutrophic water contains high levels of nutrients. As a result, the rapid addition of these nutrients favors certain types of fast-growing aquatic plants, like algae. This enables the algae to overwhelm the entire ecosystem in a short amount of time. In such circumstances, the algae may consume all the oxygen in the water, killing the other plant and animal species in the ecosystem. The process of eutrophication often occurs as a result of human interference, such as when water is exposed to fertilizers from farm runoff. Once in a eutrophic state, the water remains very ecologically resilient—that is, it is very difficult to restore the water to its former natural, healthy condition.
Background
Resilience theory is still an evolving concept. It was originally defined as the amount of external change or disturbance an ecosystem could absorb without causing fundamental changes in how it operated. Still, some scientists have suggested that resiliency is better measured by assessing how long it takes an ecosystem to be restored to its original state after a disturbance.
Such disturbances may take any number of forms. From a natural perspective, these stressors may include hurricanes, droughts, insect population explosions, and fires. Many ecosystems have developed ways to respond to recurring disturbances, such as an ecosystem that is prone to hurricanes or fires. For instance, in Florida, the Everglades developed over millennia into a complex series of interconnected ecosystems that are able to naturally absorb and filter water during periods of flooding. However, human-related triggers such as pollution, deforestation, invasive species, soil degradation, and the local extinction of essential species may result in changes that are too sudden and drastic for an ecosystem to withstand. In the case of the Everglades, alterations to the flow of water through the creation of canals and the draining of swamps resulted in episodes of severe flooding.
Canadian ecologist C.S. Holling first outlined the concept of ecological resilience in 1973. The term resilience had prior applications in other academic specialities before it was used in ecology. In fields such as engineering and psychology, resilience refers to the ability of a set of interdependent infrastructures or systems, such as a building or the human brain, to absorb or adapt to stress. Holling applied the term to describe the behavior of ecosystems when faced with disturbances. He believed that studies of ecological resilience might allow scientists to understand how environmental stressors impact the behavioral, genetic, and physiological functions of ecosystems.
Overview
Ecologists increasingly link human activity to the health of natural environments, which affects the health of human habitats as well. The environment shared by humans and the natural world is called a social-ecological system (SES). Ecological resilience is an important metric used to measure the relative health of an SES. This concept also has applications for the studies of climate change, pollution control, environmental engineering, human population management, invasive species control, sustainable development, environmental impact, and ecosystems management and restoration. Ecological resilience allows biologists to understand the impact that humans have on their environment.
The goal of studying ecological resilience is often to help build, maintain, and restore ecosystems to healthy, stable states. A resilient, healthy ecosystem is defined as an environment in which the natural mechanisms needed to maintain its stability are able to respond positively to change. The standards used to judge such criteria vary among ecosystems. For instance, the ecological resilience of coral reefs is dependent upon a coral-rich environment in which many species of coral coexist, rather than one in which one species of coral dominates or where algae becomes the principal species.
A key characteristic of a resilient ecosystem is biodiversity. A biodiverse ecosystem will typically have several species that fill the same role. For instance, in a healthy reef ecosystem, several species of herbivore fish help control algae populations. Even when faced with the loss of one such species, a resilient ecosystem will have other algae-eating fish species that fill the same functional need, allowing the reef to remain healthy.
The study of ecological resilience provides scientists with insight about how to restore or strengthen damaged ecosystems while preparing for possible changes resulting from climate change. Resiliency also allows scientists to explore how ecosystems may be best managed to provide for sustainable means of development (such as agriculture or fishing) without negatively influencing their functionality and health. Many ecologists have also adopted resilience theories as a means of establishing how human environments are inextricably linked to their natural surroundings.
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