Ecosystem collapse

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Image of the Aral Sea in 1989 (left) and 2014. The Aral Sea is an example of a collapsed ecosystem.[1] (image source: NASA)

An

biophysical environment.[2]: 458  Ecosystems are never static, and are continually subject to stabilizing and destabilizing processes alike.[3] Stabilizing processes allow ecosystems to adequately respond to destabilizing changes, or pertubations, 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 (sometimes also termed ecological collapse).[4] occurs.[5]

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

Lake Hovsgol ecosystems during the Last Glacial Maximum.[7][8]

Today, the ongoing

habitat degradation and fragmentation, which eventually destroys entire ecosystems if left unchecked.[9] 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.[10] 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.[6] 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.[11][12]

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 had existed for decades, the IUCN Red List of Ecosystems had only been in development since 2008.[1][6]

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.

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 agreatly altered structure and function.[1] There are exceptions where an ecosystem can be recovered past the point of a collapse,[13] 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.[6][1]

Drivers

A diagram of the typical drivers of ecosystem collapse.[1]

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.[14][15] 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 (and potentially irreversible) changes post-disturbance; when a system would otherwise have been able to recover.[15]

Some behaviors that induce transformation are: human intervention in the balance of local diversity (through introduction of new species or

anthropogenic climate change, and habitat destruction or fragmentation in terrestrial/marine systems.[14] 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.[16]

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.[17][18] Although states of ecosystem collapse are often defined quantitatively, few studies adequately describe transitions from pristine or original state towards collapse.[19][20]

Geological record

See also: Regime shift

In another example, 2004 research demonstrated how during the

Lake Hovsgol ecosystems, which then drove species evolution.[7] The collapse of Hovsgol's ecosystem during the LGM brought forth a new ecosystem, with limited biodiversity in species and low levels of endemism
, in Hovsgol 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

amniotes to take over (but smaller relatives of the affected ones survived also).[8]

Historic examples of collapsed ecosystems

Subtropical broadleaf forests disappeared from Easter Island. The island is currently mostly covered in grassland with nga'atu or bulrush (Schoenoplectus californicus tatora) in the crater lakes of Rano Raraku and Rano Kau.

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.[22]

The

hypersaline lakes, while dried areas have transformed into desert steppes.[1][23]

The regime shift in the northern

sardines were the dominant vertebrate consumers, but overfishing and two adverse climatic events (Benguela Niño in 1974 and 1984) lead to an impoverished ecosystem state with high biomass of jellyfish and pelagic goby.[25]

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.[10]

Contemporary risk

Log–log linear relationship between the spatial area and the temporal duration of 42 observed Earth system regime shifts[26]

There are two tools commonly used together to assess risks to ecosystems and biodiversity: generic risk assessment protocols and stochastic simulation models. The most notable of the two tactics is risk assessment protocol, particularly because of the IUCN Red List of Ecosystems (RLE), which is widely applicable to many ecosystems even in data-poor circumstances. However, because using this tool is essentially comparing systems to a list of criteria, it is often limited in its ability to look at ecosystem decline holistically; and is thus often used in conjunction with simulation models that consider more aspects of decline such as ecosystem dynamics, future threats, and social-ecological relationships.[18]

The IUCN RLE is a global standard that was developed to assess threats to various ecosystems on local, regional, national, and global scales, as well as to prompt conservation efforts in the face of the unparalleled decline of natural systems in the last decade.[20][27] And though this effort is still in the earlier stages of implementation, the IUCN has a goal to assess the risk of collapse for all of the world's ecosystems by 2025.[20] The concept of ecosystem collapse is used in the framework to establish categories of risk for ecosystems, with the category Collapsed used as the end-point of risk assessment. Other categories of threat (Vulnerable, Endangered and Critically Endangered) are defined in terms of the probability or risk of collapse.[1] A paper by Bland et al. suggests four aspects for defining ecosystem collapse in risk assessments:[19]

  1. qualitatively defining initial and collapsed states
  2. describing collapse and recovery transitions
  3. identifying and selecting indicators of collapse
  4. setting quantitative collapse thresholds.

Early detection and monitoring

Further information: Regime shift § Early-warning signals and critical slowing down
Emerging signals of declining forest resilience under climate change.[28]

Scientists can predict tipping points for ecosystem collapse. The most frequently used model for predicting food web collapse is called R50, which is a reliable measurement model for food web robustness.[29] However, there are others: i.e. marine ecosystem assessments can use RAM Legacy Stock Assessment Database. In one example, 154 different marine fish species were studied to establish the relationship between pressures on fish populations such as overfishing and climate change, these populations; traits like growth rate, and the risk of ecosystem collapse.[30]

The measurement of "critical slowing down" (CSD) is one approach for developing early warning signals for a potential or likely onset of approaching collapse. It refers to increasingly slow recovery from perturbations.[31][32]

In 2020, one paper suggested that once a 'point of no return' is reached, breakdowns do not occur gradually but rapidly and that the

savannah-type mixture of trees and grass within 50 years and the Caribbean coral reefs could collapse within 15 years once a state of collapse has been reached.[33][34][35][26] Another indicated that large ecosystem disruptions will occur earlier under more intense climate change: under the high-emissions RCP8.5 scenario, ecosystems in the tropical oceans would be the first to experience abrupt disruption before 2030, with tropical forests and polar environments following by 2050. In total, 15% of ecological assemblages would have over 20% of their species abruptly disrupted if as warming eventually reaches 4 °C (7.2 °F); in contrast, this would happen to fewer than 2% if the warming were to stay below 2 °C (3.6 °F).[36]

Rainforest collapse

Trees being felled in Kalimantan, the Indonesian part of Borneo, in 2013, to make way for a new coal mining project
Deforestation of the Amazon rainforest in Bolivia in 2016

Rainforest collapse refers to the actual past and theoretical future ecological collapse of rainforests. It may involve habitat fragmentation to the point where little rainforest biome is left, and rainforest species only survive in isolated refugia. Habitat fragmentation can be caused by roads. When humans start to cut down the trees for logging, secondary roads are created that will go unused after its primary use. Once abandoned, the plants of the rainforest will find it difficult to grow back in that area.[37] Forest fragmentation also opens the path for illegal hunting. Species have a hard time finding a new place to settle in these fragments causing ecological collapse. This leads to extinction of many animals in the rainforest.

A classic pattern of

forest fragmentation is occurring in many rainforests including those of the Amazon, specifically a 'fishbone' pattern formed by the development of roads into the forest. This is of great concern, not only because of the loss of a biome with many untapped resources and wholesale death of living organisms, but also because plant and animal species extinction is known to correlate with habitat fragmentation.[38]

In the year 2022, research found that more than three-quarters of the Amazon rainforest has been losing resilience due to deforestation and climate change since the early 2000s as measured by recovery-time from short-term perturbations (the critical slowing down), reinforcing the theory that it is approaching a critical transition.[12][11] Another study from 2022 found that that tropical, arid and temperate forests are substantially losing resilience.[28][39]

Coral reefs

See also: Environmental issues with coral reefs

A major concern for

marine biologists is the collapse of coral reef ecosystems.[40]). An effect of global climate change is the rising sea levels which can lead to reef drowning or coral bleaching.[40] Human activity, such as fishing, mining, deforestation, etc., serves as a threat for coral reefs by affecting the niche of the coral reefs. For example, there is a demonstrated correlation between a loss in diversity of coral reefs by 30-60% and human activity such as sewage and/or industrial pollution.[41]

This section is an excerpt from Extinction risk from climate change § Corals.[edit]
Coral reefs off Raja Ampat Islands in New Guinea.
Almost no other ecosystem is as vulnerable to climate change as coral reefs. Updated 2022 estimates show that even at 1.5 °C (2.7 °F), only 0.2% of the world's coral reefs would still be able to withstand marine heatwaves, as opposed to 84% being able to do so now, with the figure dropping to 0% by 2 °C (3.6 °F) and beyond.[42][43] However, it was found in 2021 that each square meter of coral reef area contains about 30 individual corals, and their total number is estimated at half a trillion - equivalent to all the trees in the Amazon, or all the birds in the world. As such, most individual coral reef species are predicted to avoid extinction even as coral reefs would cease to function as the ecosystems we know.[44][45] A 2013 study found that 47–73 coral species (6–9%) are vulnerable to climate change while already threatened with extinction according to the IUCN Red List, and 74–174 (9–22%) coral species were not vulnerable to extinction at the time of publication, but could be threatened under continued climate change, making them a future conservation priority.[46] The authors of the recent coral number estimates suggest that those older projections were too high, although this has been disputed.[44][47][48]

Conservation and reversal

See also:
Restoration ecology and Conservation biology

As of now there is still not much information on effective conservation or reversal methods for ecosystem collapse. Rather, there has been increased focus on the predictability of ecosystem collapse, whether it is possible, and whether it is productive to explore.[20] This is likely because thorough studies of at-risk ecosystems are a more recent development and trend in ecological fields, so collapse dynamics are either too recent to observe or still emerging. Since studies are not yet long term, conclusions about reversibility or transformation potential are often hard to draw from newer, more focused studies.[5]

See also

References

  1. ^
    PMID 23667454. Archived from the original
    on 28 October 2020. Retrieved 8 September 2018.
  2. OCLC 755081405
    .
  3. doi:10.1038/nature10832
    .
  4. ^ "Ecological collapse". The Global Challenges Foundation. Retrieved 2021-12-03.
  5. ^
    S2CID 237994459
    .
  6. ^
    hdl:10536/DRO/DU:30148368
    .
  7. ^
    doi:10.1016/j.palaeo.2004.02.017
    .
  8. ^
    doi:10.1130/G31182.1
    .
  9. ^ "Living Planet Report". World Wildlife Fund.
  10. ^ a b Hamilton, Lawrence C.; Butler, M. J. (January 2001). "Outport adaptations: Social indicators through Newfoundland's Cod crisis". Human Ecology Review. 8 (2): 1–11.
  11. ^
    S2CID 234889502
    .
  12. ^ a b Carrington, Damian (7 March 2022). "Climate crisis: Amazon rainforest tipping point is looming, data shows". The Guardian. Retrieved 18 April 2022.
  13. hdl:11573/624610
    .
  14. ^ a b "Ecological collapse". The Global Challenges Foundation. Retrieved 2021-12-03.
  15. ^
    S2CID 4320064
    .
  16. S2CID 128464303
    .
  17. hdl:10278/3671359
    .
  18. ^
    PMID 28931744. Archived from the original
    on 28 October 2020. Retrieved 9 September 2018.
  19. ^
    hdl:11343/283474
    .
  20. ^
    S2CID 90179066
    .
  21. S2CID 31953303
    .
  22. doi:10.1016/j.jas.2009.10.006
    .
  23. ^ Philip Micklin; Nikolay V. Aladin (March 2008). "Reclaiming the Aral Sea". Scientific American. Retrieved 17 May 2008.
  24. S2CID 92093006
    .
  25. ISSN 0304-3800
    .
  26. ^
    PMID 32157098
    .
  27. ^ "Red List of Ecosystems". IUCN. 2015-12-08. Retrieved 2021-12-07.
  28. ^
    PMID 35831499
    .
  29. ISSN 1600-0706
    .
  30. PMID 26246548
    .
  31. PMID 25422412
    .
  32. S2CID 6916712
    .
  33. ^ "Ecosystems the size of Amazon 'can collapse within decades'". The Guardian. 10 March 2020. Retrieved 10 March 2020.
  34. ^ "Amazon rainforest could be gone within a lifetime". EurekAlert!. 10 March 2020. Retrieved 10 March 2020.
  35. ^ "Ecosystems the size of Amazon 'can collapse within decades'". The Guardian. 10 March 2020. Retrieved 13 April 2020.
  36. S2CID 256822113
    .
  37. ISSN 2150-8925
    .
  38. ^ Rosenzweig, Michael L. (1995). Species diversity in space & time. Cambridge, United Kingdom: Cambridge University Press.
  39. ^ "Forests are becoming less resilient because of climate change". New Scientist. Retrieved 21 August 2022.
  40. ^
    PMID 11344288
    .
  41. doi:10.1016/S0025-326X(98)00047-2
    .
  42. S2CID 246512448
    .
  43. ^ Dunne, Daisy (1 February 2022). "Last refuges for coral reefs to disappear above 1.5C of global warming, study finds". Carbon Brief.
  44. ^
    S2CID 256726373
    .
  45. ^ "Half a trillion corals: World-first coral count prompts rethink of extinction risks". Phys.org. 1 March 2021.
  46. PMID 23950785
    .
  47. S2CID 246827109
    .
  48. S2CID 246826874
    .
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