Ecosystem collapse
An ecosystem, short for ecological system, is defined as a collection of interacting organisms within a biophysical environment. Ecosystems are never static, and are continually subject to both stabilizing and destabilizing processes. Stabilizing processes allow ecosystems to adequately respond to destabilizing changes, or perturbations, in ecological conditions, or to recover from degradation induced by them. Yet, if destabilizing processes become strong enough or fast enough to cross a critical threshold within that ecosystem, often described as an ecological 'tipping point', then an ecosystem collapse occurs.
Ecosystem collapse does not mean total disappearance of life from the area, but it does result in the loss of the original ecosystem's defining characteristics, typically including the ecosystem services it may have provided. Collapse of an ecosystem is effectively irreversible more often than not, and even if the reversal is possible, it tends to be slow and difficult. Ecosystems with low resilience may collapse even during a comparatively stable time, which then typically leads to their replacement with a more resilient system in the biosphere. However, even resilient ecosystems may disappear during the times of rapid environmental change, and study of the fossil record was able to identify how certain ecosystems went through a collapse, such as with the Carboniferous rainforest collapse or the collapse of Lake Baikal and Lake Hovsgol ecosystems during the Last Glacial Maximum.
Today, the ongoing Holocene extinction is caused primarily by human impact on the environment, and the greatest biodiversity loss so far had been due to habitat degradation and fragmentation, which eventually destroys entire ecosystems if left unchecked. There have been multiple notable examples of such an ecosystem collapse in the recent past, such as the collapse of the Atlantic northwest cod fishery. More are likely to occur without a change in course, since estimates show that 87% of oceans and 77% of the land surface have been altered by humanity, with 30% of global land area is degraded and a global decline in ecosystem resilience. Deforestation of the Amazon rainforest is the most dramatic example of a massive, continuous ecosystem and a biodiversity hotspot being under the immediate threat from habitat destruction through logging, and the less-visible, yet ever-growing and persistent threat from climate change.
Biological conservation can help to preserve threatened species and threatened ecosystems alike. However, time is of the essence. Just as interventions to preserve a species have to occur before it falls below viable population limits, at which point an extinction debt occurs regardless of what comes after, efforts to protect ecosystems must occur in response to early warning signals, before the tipping point to a regime shift is crossed. Further, there is a substantial gap between the extent of scientific knowledge how extinctions occur, and the knowledge about how ecosystems collapse. While there have been efforts to create objective criteria used to determine when an ecosystem is at risk of collapsing, they are comparatively recent, and are not yet as comprehensive. While the IUCN Red List of threatened species has existed for decades, the IUCN Red List of Ecosystems has only been in development since 2008.
Definition
Ecosystem collapse has been defined as a "transformation of identity, loss of defining features, and replacement by a novel ecosystem", and involves the loss of "defining biotic or abiotic features", including the ability to sustain the species which used to be associated with that ecosystem. According to another definition, it is "a change from a baseline state beyond the point where an ecosystem has lost key defining features and functions, and is characterised by declining spatial extent, increased environmental degradation, decreases in, or loss of, key species, disruption of biotic processes, and ultimately loss of ecosystem services and functions". Ecosystem collapse has also been described as "an analogue of species extinction", and in many cases, it is irreversible, with a new ecosystem appearing instead, which may retain some characteristics of the previous ecosystem, yet has a greatly altered structure and function. There are exceptions where an ecosystem can be recovered past the point of a collapse, but by definition, will always be far more difficult to reverse than allowing a disturbed yet functioning ecosystem to recover, requiring active intervention and/or a prolonged period of time even if it can be reversed.Drivers
While collapse events can occur naturally with disturbances to an ecosystem—through fires, landslides, flooding, severe weather events, disease, or species invasion—there has been a noticeable increase in human-caused disturbances over the past fifty years. The combination of environmental change and the presence of human activity is increasingly detrimental to ecosystems of all types, as our unrestricted actions often increase the risk of abrupt changes post-disturbance; when a system would otherwise have been able to recover.Some behaviors that induce transformation are: human intervention in the balance of local diversity, alterations in the chemical balance of environments through pollution, modifications of local climate or weather with anthropogenic climate change, and habitat destruction or fragmentation in terrestrial/marine systems. For instance, overgrazing was found to cause land degradation, specifically in Southern Europe, which is another driver of ecological collapse and natural landscape loss. Proper management of pastoral landscapes can mitigate risk of desertification.
Despite the strong empirical evidence and highly visible collapse-inducing disturbances, anticipating collapse is a complex problem. The collapse can happen when the ecosystem's distribution decreases below a minimal sustainable size, or when key biotic processes and features disappear due to environmental degradation or disruption of biotic interactions. These different pathways to collapse can be used as criteria for estimating the risk of ecosystem collapse. Although states of ecosystem collapse are often defined quantitatively, few studies adequately describe transitions from pristine or original state towards collapse.
Geological record
In another example, 2004 research demonstrated how during the Last Glacial Maximum, alternations in the environment and climate led to a collapse of Lake Baikal and Lake Hovsgol ecosystems, which then drove species evolution. The collapse of Hovsgol's ecosystem during the LGM brought forth a new ecosystem, with limited biodiversity in species and low levels of endemism during the Holocene. That research also shows how ecosystem collapse during LGM in Lake Hovsgol led to higher levels of diversity and higher levels of endemism as a byproduct of subsequent evolution.In the Carboniferous period, coal forests, great tropical wetlands, extended over much of Euramerica. This land supported towering lycopsids which fragmented and collapsed abruptly. The collapse of the rainforests during the Carboniferous has been attributed to multiple causes, including climate change and volcanism. Specifically, at this time climate became cooler and drier, conditions that are not favourable to the growth of rainforests and much of the biodiversity within them. The sudden collapse in the terrestrial environment made many large vascular plants, giant arthropods, and diverse amphibians to go extinct, allowing seed-bearing plants and amniotes to take over.
Historic examples of collapsed ecosystems
The Rapa Nui subtropical broadleaf forests in Easter Island, formerly dominated by an endemic Palm, are considered collapsed due to the combined effects of overexplotaition, climate change and introduced exotic rats.The Aral Sea was an endorheic lake between Kazakhstan and Uzbekistan. It was once considered one of the largest lakes in the world but has been shrinking since the 1960s after the rivers that fed it were diverted for large scale irrigation. By 1997, it had declined to 10% of its original size, splitting into much smaller hypersaline lakes, while dried areas have transformed into desert steppes.
The regime shift in the northern Benguela upwelling ecosystem is considered an example of ecosystem collapse in open marine environments. Prior to the 1970s sardines were the dominant vertebrate consumers, but overfishing and two adverse climatic events lead to an impoverished ecosystem state with high biomass of jellyfish and pelagic goby.
Another notable example is the collapse of the Grand Banks cod in the early 1990s, when overfishing reduced fish populations to 1% of their historical levels.
Currently collapsing
It's not currently considered collapsed, but well on the way if there is no intervention.Northerns Savannas of Australia, The Kimberley and the Cape York Peninsula. Both are considered some of the largest intact ecosystems, with the Kimberley containing 2,000 native plants and the Cape containing roughly 3,000. Both home hundreds of birds, mammals, reptiles, and insects alike. Due to fire-promoting weeds, the landscape has changed from woodlands to grasslands over the years. Added pressures from climate change, overgrazing, and forestry has started to make a significant decline.
The Northern Mangroves in Australia continue to lose nutrients and landmass. Approximately 7,400 hectares of the mangroves were lost in the largest die back recorded between 2015 and 2016.
The Great Barrier Reef recorded its first bleaching event in 1998, and the largest bleaching spread occurred in 2020. It is recorded that roughly 50% of the coral has been lost, as of 2023. As the coral bleaches, it is not only dying, but the organisms that rely on it for survival are being impacted as well. It is assumed the Great Barrier Reef supports over 9,000 organisms. The continued decline of the Great Barrier Reef is due to many factors, the largest being Climate Change and pollution.
World Heritage Site: Shark Bay is considered the most venerable according to the . The ecosystem supports the community but decline due to global warming and climate change have heavily affected this. The sea grass is not sustainable with changing climates and that is the main source of habitat for the fish and marine life.
Great Salt Lake of Utah is considered a keystone ecosystem and economic dependent factor for the state of Utah. It has lost over 73% of its water and 60% surface area since 1850. Unless drastic measures are taken, the lake is expected to completely dry up and cause irreparable damage that will impact the wellbeing of the wildlife, public health, environmental decline, and economic decline.