Climate and plant community diversity in space and time.

Climate strongly shapes plant diversity over large spatial scales, with relatively warm and wet (benign, productive) regions supporting greater numbers of species. Unresolved aspects of this relationship include what causes it, whether it permeates to community diversity at smaller spatial scales, whether it is accompanied by patterns in functional and phylogenetic diversity as some hypotheses predict, and whether it is paralleled by climate-driven changes in diversity over time. Here, studies of Californian plants are reviewed and new analyses are conducted to synthesize climate-diversity relationships in space and time. Across spatial scales and organizational levels, plant diversity is maximized in more productive (wetter) climates, and these consistent spatial relationships are mirrored in losses of taxonomic, functional, and phylogenetic diversity over time during a recent climatic drying trend. These results support the tolerance and climatic niche conservatism hypotheses for climate-diversity relationships, and suggest there is some predictability to future changes in diversity in water-limited climates

Long-term shifts in the patterns and underlying processes of plant associations in Wisconsin forests

© 2016 John Wiley & Sons Ltd. Aim: Plant species co-occur within communities in response to variation in environmental conditions, limited species dispersal and biotic interactions. We used surveys and resurveys of the same sites of three temperate forest plant communities to study patterns of association between co-occurring species pairs and to infer how these mechanisms contribute to community assembly. Our goal was to compare these forces among communities occupying more and less disturbed landscapes and examine how these have changed over the last 50 years. Location: Wisconsin, USA. Methods: We resurveyed 266 sites first surveyed in the 1950s to assess the patterns and dynamics of co-occurrence among understorey plant species in three community types. We then used checkerboard scores, null models and a newly developed framework to infer the mechanisms likely to have driven community assembly. Finally, we compared these across the three communities and two time periods. Results: Species co-occur less often than expected in all three vegetation types and both periods. We detected high fractions of aggregated and segregated species pairs (up to 14% and 17%, respectively). In the fragmented southern upland forests and central sand plains, both biotic interactions and dispersal limitation may play important roles in community assembly with inferred dispersal limitation becoming more important since the 1950s. In the more continuous and intact northern upland forests, environmental filtering and biotic interactions appear to dominate community dynamics with little change over time. Aggregated and segregated species pairs made a similar contribution to our ability to infer these mechanisms. Main conclusions: Environmental filtering, biotic interactions and dispersal limitation all appear to affect plant community structure in both time periods. However, the influence of dispersal limitation seems to be increasing in more fragmented forest landscapes, portending shifts in community composition and dynamics. Because aggregated and segregated species pairs may be shaped by similar processes both can be used to infer processes of community assembly

Fire exclusion and climate change interact to affect long-term changes in the functional composition of plant communities

© 2017 John Wiley & Sons Ltd Aim: Plant functional traits allow us to mechanistically link changes in species composition to changes in ecosystem functions. Understanding how and why changes occur in functional composition of plant communities can thus help us better conserve and restore biodiversity. We aim to examine long-term effects of fire exclusion and climate change on the functional composition of fire-maintained pine barrens in central Wisconsin. Location: Central Wisconsin, USA. Methods: Using a database that included vegetation data of surveys (1958) and resurveys (2012) of 30 sites, we quantified functional composition (α and β functional diversity, community-weighted means) of each site at both time periods. We then applied linear regression and linear mixed models to study effects of fire exclusion and climate change on changes in functional composition. Results: We observed shifts towards larger specific leaf area, greater seed mass and other traits related to shade tolerance. These communities thus appear to be undergoing ecological succession, favouring plant adaptions to better harvest light and carbon in darker, warmer and wetter habitats. Functional alpha diversity increased, while functional beta diversity decreased even after controlling for changes in taxonomic diversity. Fire exclusion and climate change both contributed to these increases in local functional diversity but neither is related to the functional homogenization observed. Fire exclusion and climate change also interacted negatively to affect local functional diversity, suggesting that future climate change and succession may soon reduce alpha functional diversity. Main conclusions: Our study provides a rare record of long-term functional dynamics and demonstrates that fire exclusion and climate change can interact to affect the functional composition of plant communities. Thus, we should consider changes in local ecological conditions as we seek to predict how climate change will affect the functional composition of plant communities

Drivers of observed biotic homogenization in pine barrens of central wisconsin

© 2015 by the Ecological Society of America. Fire suppression throughout the 20th century greatly altered plant communities in fire-dominated systems across North America. Our ability to assess these effects over the long term, however, is handicapped by the paucity of baseline data. Here, we used detailed baseline data from the 1950s to track changes in the over- and understory composition of pinebarrens vegetation growing on sandy, glacial lake-bed sediments in central Wisconsin. We expected fire suppression to favor succession to closed-canopy conditions, leading to decreases in shade-intolerant and fire-Adapted species and consequent reductions in alpha and gamma diversity. We also expected beta diversity to decline due to increases in shade-tolerant, firesensitive, and exotic species. In fact, fire suppression has greatly altered the structure and composition of these pine-barrens communities over the past 54 years. Woody, windpollinated, and shade-tolerant species all increased in richness and abundance, as expected, with succession following fire suppression. Contrary to expectations, local and regional species richness increased by 12% and 26%, respectively, while Shannon beta diversity declined 24.1%. Increases in canopy coverage and number of native species appear to have driven this biotic homogenization. In contrast, increases in exotic species in our study did not promote biotic homogenization, reflecting their relative rarity across sites. Our findings highlight the key role fire plays in shaping the assembly of these pine-barrens communities

Climate drives loss of phylogenetic diversity in a grassland community

© 2019 National Academy of Sciences. All rights reserved. While climate change has already profoundly influenced biodiversity through local extinctions, range shifts, and altered interactions, its effects on the evolutionary history contained within sets of coexisting species—or phylogenetic community diversity—have yet to be documented. Phylogenetic community diversity may be a proxy for the diversity of functional strategies that can help sustain ecological systems in the face of disturbances. Under climatic warming, phylogenetic diversity may be especially vulnerable to decline in plant communities in warm, water-limited regions, as intensified water stress eliminates drought-intolerant species that may be relicts of past wetter climates and may be distantly related to coexisting species. Here, we document a 19-y decline of phylogenetic diversity in a grassland community as moisture became less abundant and predictable at a critical time of the year. This decline was strongest in native forbs, particularly those with high specific leaf area, a trait indicating drought sensitivity. This decline occurred at the small spatial scale where species interact, but the larger regional community has so far been buffered against loss of phylogenetic diversity by its high levels of physical and biotic heterogeneity

Can functional traits account for phylogenetic signal in community composition?

© 2017 The Authors. New Phytologist © 2017 New Phytologist Trust Phylogenetic and functional trait-based analyses inform our understanding of community composition, yet methods for quantifying the overlap in information derived from functional traits and phylogenies remain underdeveloped. Does adding traits to analyses of community composition reduce the phylogenetic signal in the residual variation? If not, then measured functional traits alone may be insufficient to explain community assembly. We propose a general statistical framework to quantify the proportion of phylogenetic pattern in community composition that remains after including measured functional traits. We then illustrate the framework with applications to two empirical data sets. Both data sets showed strong phylogenetic attraction, with related species likely to co-occur in the same communities. In one data set, including traits eliminated all phylogenetic signals in the residual variation of both abundance and presence/absence patterns. In the second data set, including traits reduced phylogenetic signal in residuals by 25% and 98% for abundance and presence/absence data, respectively. Our framework provides an explicit way to estimate how much phylogenetic community pattern remains in the residual variation after including measured functional traits. Knowing that functional traits account for most of the phylogenetic pattern should provide confidence that important traits for phylogenetic community structure have been identified. Conversely, knowing that there is unexplained residual phylogenetic information should spur the search for additional functional traits or other processes underlying community assembly

Species richness and phylogenetic diversity of native and non-native species respond differently to area and environmental factors

© 2018 John Wiley & Sons Ltd Aim: To test whether native and non-native species have similar diversity–area relationships (species–area relationships [SARs] and phylogenetic diversity–area relationships [PDARs]) and whether they respond similarly to environmental variables. Location: United States. Methods: Using lists of native and non-native species as well as environmental variables for \u3e250 US national parks, we compared SARs and PDARs of native and non-native species to test whether they respond similarly to environmental conditions. We then used multiple regressions involving climate, land cover and anthropogenic variables to further explore underlying predictors of diversity for plants and birds in US national parks. Results: Native and non-native species had different slopes for SARs and PDARs, with significantly higher slopes for native species. Corroborating this pattern, multiple regressions showed that native and non-native diversity of plants and birds responded differently to a greater number of environmental variables than expected by chance. For native species richness, park area and longitude were the most important variables while the number of park visitors, temperature and the percentage of natural area were among the most important ones for non-native species richness. Interestingly, the most important predictor of native and non-native plant phylogenetic diversity, temperature, had positive effects on non-native plants but negative effects on natives. Main conclusions: SARs, PDARs and multiple regressions all suggest that native and non-native plants and birds responded differently to environmental factors that influence their diversity. The agreement between diversity–area relationships and multiple regressions with environmental variables suggests that SARs and PDARs can be both used as quick proxies of overall responses of species to environmental conditions. However, more importantly, our results suggest that global change will have different effects on native and non-native species, making it inappropriate to apply the large body of knowledge on native species to understand patterns of community assembly of non-native species

Body size trends in response to climate and urbanization in the widespread North American deer mouse, Peromyscus maniculatus

© 2020, The Author(s). Body size decline is hypothesized to be a key response to climate warming, including warming driven by urban heat islands. However, urbanization may also generate selective gradients for body size increases in smaller endotherms via habitat fragmentation. Here we utilize a densely sampled, multi-source dataset to examine how climate and urbanization affect body size of Peromyscus maniculatus (PEMA), an abundant rodent found across North America. We predicted PEMA would conform to Bergmann’s Rule, e.g. larger individuals in colder climates, spatially and temporally. Hypotheses regarding body size in relation to urbanization are less clear; however, with increased food resources due to greater anthropogenic activity, we expected an increase in PEMA size. Spatial mixed-models showed that PEMA conform to Bergmann’s Rule and that PEMA were shorter in more urbanized areas. With the inclusion of decade in mixed-models, we found PEMA mass, but not length, is decreasing over time irrespective of climate or population density. We also unexpectedly found that, over time, smaller-bodied populations of PEMA are getting larger, while larger-bodied populations are getting smaller. Our work highlights the importance of using dense spatiotemporal datasets, and modeling frameworks that account for bias, to better disentangle broad-scale climatic and urbanization effects on body size