Ecosystem collapse
[7][8] 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.
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.
[1] 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".
[15] Some behaviors that induce transformation are: human intervention in the balance of local diversity (through introduction of new species or overexploitation), 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.
[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.
[16] Despite the strong empirical evidence and highly visible collapse-inducing disturbances, anticipating collapse is a complex problem.
In the Carboniferous period, coal forests, great tropical wetlands, extended over much of Euramerica (Europe and America).
[8] 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.
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.
[24] Prior to the 1970s 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.
[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.
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.
An effect of global climate change is the rising sea levels which can lead to reef drowning or coral bleaching.
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.
