Temporal and spatial biogeographical boundaries are usually associated with extinction processes. However, some boundary regions seem to be places of speciation. It is unclear if boundaries are favored by generalized or specialized species. Recent studies suggest that narrow-ranging species can be strong competitors and they can replace wide-ranging species while shifting their range boundaries under the effect of climate change. In other boundary regions, the decline of both passive-and active-dispersing specialists has been observed. Core regions are also weakening. They are jeopardized mainly by extreme climate events and fragmentation and by the accompanied non-native invasions. Biodiversity loss and homogenization have been observed globally.
The synergistic effects of direct human perturbations and climate change have been causing the mass extinction of species. Here, I present the deterministic factors of collapses in present ecosystems. I captured and synthesized the key deterministic traits and processes before a collapse in the peer-reviewed literature. The results of the literature review show that deterministic factors can be used as early warning signals of collapses. The literature also suggests that we have entered the middle stage of global mass extinction, which may be irreversible.
We studied similarities of collapses and concluded that dominant species have a universal effect on the pattern of collapses. We used open paleoecological and modern data to detect ‘early warning signals’ of collapses. We tested and ranked collapse indicators at the community level (abundance, species richness, constancy, dominance, Shannon’s H, standard deviation, variance, lag-1 autocorrelation of community abundance, lag-1 autocorrelation of Shannon’s H) and at the level of the dominant species (total changes of pre-collapse and collapse dominant species, lag-1 autocorrelation of pre-collapse and collapse dominant species) based on their performances. We distinguished between small-scale signals (sharp drops and peaks) and large-scale signals (trend changes). Small-scale signals and large-scale signals can be at the same time, however, small-scale signals can also precede large-scale signals. Small-scale signals indicate environmental events. Large-scale trend changes refer to the decline and eventually the collapse of the community. Our results show that the collapse indicators of the dominant species outperform community-level critical slowing down indicators, which suggests that the dominant species probably have an important role in community-level collapses triggered by environmental events. We also concluded that unusual environmental events might be the number one cause of collapses therefore small-scale signals should be involved in analyses.
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