Holocene shifts in the assembly of plant and animal communities implicate human impacts

Abstract

Understanding how ecological communities are organized and how they change through time is critical to predicting the effects of climate change. Recent work documenting the co-occurrence structure of modern communities found that most significant species pairs co-occur less frequently than would be expected by chance. However, little is known about how co-occurrence structure changes through time. Here we evaluate changes in plant and animal community organization over geological time by quantifying the co-occurrence structure of 359,896 unique taxon pairs in 80 assemblages spanning the past 300 million years. Co-occurrences of most taxon pairs were statistically random, but a significant fraction were spatially aggregated or segregated. Aggregated pairs dominated from the Carboniferous period (307 million years ago) to the early Holocene epoch (11,700 years before present), when there was a pronounced shift to more segregated pairs, a trend that continues in modern assemblages. The shift began during the Holocene and coincided with increasing human population size and the spread of agriculture in North America. Before the shift, an average of 64% of significant pairs were aggregated; after the shift, the average dropped to 37%. The organization of modern and late Holocene plant and animal assemblages differs fundamentally from that of assemblages over the past 300 million years that predate the large-scale impacts of humans. Our results suggest that the rules governing the assembly of communities have recently been changed by human activity.

Climate legacies drive global soil carbon stocks in terrestrial ecosystems

“…Therefore, the paleoclimatic footprint is difficult to observe in these areas. Together, our findings accord with recent studies highlighting the importance of past climate as a driver of ecosystem attributes, such as litter decomposition and biodiversity in terrestrial ecosystems ( 6 , 27 , 28 ), and provide, to the best of our knowledge, the first empirical demonstration that climatic legacies continue to drive the magnitude of contemporary soil C stocks at regional and global scales in terrestrial ecosystems.…”

Incorporating Temporal and Spatial Variations of Groundwater into the Construction of a Water-Based Ecological Network: A Case Study in Denko County

“…Based on the results of the point pattern analysis in this study, the spatial patterns of water nodes are characterized by a small-scale highly aggregated distribution and a large-scale uniform distribution. This pattern was the same as the findings of other research on plant communities [54], animal communities [55], and virus distribution [56], and is prevalent in natural and even human social networks. This small-scale clustering distribution and large-scale uniform distribution can ensure the sustainable and stable development of a community.…”

Sympatry or syntopy? Investigating drivers of distribution and co‐occurrence for two imperiled sea turtle species in Gulf of Mexico neritic waters

“…Analyses on plant and mammal communities across geological time have shown that aggregated species were more common before the increase in human population during the Holocene, suggesting that current evidence for sympatry and syntopy may also be impacted by human activity (Lyons et al, 2016). As these two sea turtle species evolved about 3-6 million years before this Holocene shift (Bowen, Meylan, & Avise, 1991), it is possible that the distributions we see today might be more constricted than in the past.…”