Abstract
We studied the patterns of pre-collapse communities, the small-scale and the large-scale signals of collapses, and the environmental events before the collapses using four paleoecological and one modern data series. We applied and evaluated eight indicators in our analysis: the relative abundance of species, hierarchical cluster analysis, principal component analysis, total abundance, species richness, standard deviation (without a rolling window), first-order autoregression, and the relative abundance of the dominant species. We investigated the signals at the probable collapse triggering unusual environmental events and at the collapse zone boundaries, respectively. We also distinguished between pulse and step environmental events to see what signals the indicators give at these two different types of events. Our results show that first-order autoregression is not a good environmental event indicator, but it can forecast or indicate the collapse zones in climate change. The rest of the indicators are more sensitive to the pulse events than to the step events. Step events during climate change might have an essential role in initiating collapses. These events probably push the communities with low resilience beyond a critical threshold, so it is crucial to detect them. Before collapses, the total abundance and the species richness increase, the relative abundance of the species decreases. The hierarchical cluster analysis and the relative abundance of species together designate the collapse zone boundaries. We suggest that small-scale signals should be involved in analyses because they are often earlier than large-scale signals.
Highlights
The current climate change and the ongoing sixth mass extinction (Barnosky et al, 2011) highlight the importance of research on community collapses (Henderson, 2007; Lever et al, 2014; Dakos & Bascompte, 2014; Hufnagel et al, 2020)
Besides using community-level indicators, we introduced a new indicator at the species level: the relative abundance of the dominant species
As unusual environmental events are an interest of this study, we examined whether the indicators are sensitive to pulse events, step events, collapse zone boundaries, and what signals they give
Summary
The current climate change and the ongoing sixth mass extinction (Barnosky et al, 2011) highlight the importance of research on community collapses (Henderson, 2007; Lever et al, 2014; Dakos & Bascompte, 2014; Hufnagel et al, 2020). We believe that communities show changes in their patterns long before collapses. Unusual or extreme environmental events are sudden and of great magnitude. They can be pulse events or step events. We can describe pulse events as a sudden and significant change of system parameters for a short period, for example, bolide events, volcanic eruptions, sudden, temporary cooling or warming, fires. Unusual environmental events are stochastic, and it is difficult or impossible to predetermine their time windows. These events probably have an essential role in the initiation of community collapses. Step events are PaleoceneEocene Thermal Maximum, Arctic warming events during the 1920s–1940s, presumed EM2, EM1
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