Abstract
The late Quaternary of North America was marked by prominent ecological changes, including the end‐Pleistocene megafaunal extinction, the spread of human settlements and the rise of agriculture. Here we examine the mechanistic reasons for temporal changes in mammal species association and body size during this time period. Building upon the co‐occurrence results from Lyons et al. (2016) – wherein each species pair was classified as spatially aggregated, segregated or random – we examined body mass differences (BMD) between each species pair for each association type and time period (Late Pleistocene: 40 000 14C–11 700 14C ybp, Holocene: 11 700 14C–50 ybp and Modern: 50–0 yr). In the Late Pleistocene and Holocene, the BMD of both aggregated and segregated species pairs was significantly smaller than the BMD of random pairs. These results are consistent with environmental filtering and competition as important drivers of community structure in both time periods. Modern assemblages showed a breakdown between BMD and co‐occurrence patterns: the average BMD of aggregated, segregated and random species pairs did not differ from each other. Collectively, these results indicate that the late Quaternary mammalian extinctions not only eliminated many large‐bodied species but were followed by a re‐organization of communities that altered patterns of species coexistence and associated differences in body size.
Highlights
Classical niche theory suggests that trait-based approaches can be used to study the processes underlying patterns of association among species (Weiher and Keddy 1995, Kraft et al 2008)
It was rare for aggregations to become segregations and vice versa; most pairs tended to transition from aggregated to random or from random to segregated from the Late Pleistocene to the Holocene (Fig. 1)
During the Late Pleistocene and Holocene, aggregated and segregated species pairs were more similar in body mass than random pairs (Fig. 2)
Summary
Classical niche theory suggests that trait-based approaches can be used to study the processes underlying patterns of association among species (Weiher and Keddy 1995, Kraft et al 2008). Such processes include habitat filtering (Belmaker and Jetz 2011), biotic interactions [e.g. competition (HilleRisLambers et al 2012)] or dispersal limitation (Hubbell 2001). Species with widely diverging habitat preferences or environmental tolerances co-occur less frequently and have different traits (Cornwell et al 2006, Kraft and Ackerly 2010) Biotic interactions, such as competition for the same resources, can cause species that have similar traits to exclude one another if competition is strong (Hardin 1960, Belmaker and Jetz 2015). Coexistence of species may be constrained by dispersal limitation, such as geographic or climatic barriers (Condit et al 2000, Hubbell 2001)
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