The abiotic and biotic environment together predict plant, mammal, and bird diversity and turnover across the United States

The distribution of taxonomic, phylogenetic, and functional biodiversity results from a combination of abiotic and biotic drivers which are scale dependent. Parsing the relative influence of these drivers is critical to understanding the processes underlying species assembly and generating predictions of biodiversity across taxonomic groups and for novel sites. However, doing so requires data that capture a spatial extent large enough to reflect broad-scale dynamics such as speciation and biogeography, and a spatial grain fine enough to detect local-scale dynamics like environmental filtering and biotic interactions. We used species inventories of vascular plants, birds, and mammals collected by the U.S. National Ecological Observatory Network (NEON) at 38 terrestrial field sites, to explore the processes underlying taxonomic, phylogenetic, and functional diversity and turnover. We found that, for both species richness (alpha-diversity) and turnover (beta-diversity), taxonomic, phylogenetic, and functional diversity are weak proxies for one-another, and thus may capture different species assembly processes. All diversity metrics were best predicted by a combination of abiotic and biotic variables. Taxonomic and phylogenetic richness tended to be higher at warmer, wetter sites, reflecting the role energy inputs play in driving broad-scale diversity. However, plant diversity was negatively correlated with bird phylogenetic and mammal functional diversity, implying trait conservation in plant communities may limit niche availability for consumer species. Equally, turnover in bird and mammal species across sites were associated with plant turnover. That the biodiversity of one taxon is predictive of another across these North American sites, even when controlling for environment, supports a role for the cross-clade biotic environment in driving species assembly.

The Dessau Grassland Experiment—Impact of Fertilization on Forage Quality and Species Assembly in a Species-Rich Alluvial Meadow

Since alluvial meadows of river valleys of the Cnidion dubii are protected by the EU Habitats Directive, reconciling farmers’ demands for forage quality with the objective of maintaining them in good conservation status is an important issue in grassland research. In a long-term experiment from 2010 to 2018, we investigated the impact of fertilizing on forage quality and species assembly on a species-rich and twice-mown alluvial grassland in the Dessau Elbe floodplain (Germany). The experiment was composed of an unfertilized control, PK, N60, N60PK and N120PK applications. A significant improvement in forage quality was achieved by nitrogen fertilization only for crude protein, with higher feeding requirements for sheep met only in individual years. The legume cycle was inhibited by the application of nitrogen and high grass cover was maintained, but not increased, at the highest nitrogen application after an exceptional summer flood. The target forbs persisted in numbers over the study period in all treatments. For cover, the low-competitive target forbs responded neutrally to nitrogen fertilization, whereas detrimental effects were demonstrated for the competitive ones. Thus, we recommend not applying more than 60 kg year−1 of nitrogen and only in combination with phosphorus and potassium.

Varying richness need not imply non-random species co-occurrence: implications for specifying null models

BackgroundNon-random species co-occurrence is of fundamental interest to ecologists. One approach to analysing non-random patterns is null modelling. This involves calculation of a metric for the observed dataset, and comparison to a distribution obtained by repeatedly randomising the data. Choice of randomisation algorithm, specifically whether null model species richness is fixed at that of the observed dataset, is likely to affect model results. This is particularly important in cases when there is high variation in species richness between sampling units in the observed data.MethodsHere I demonstrate the effects of accounting for variation in species richness. I use the C-score, a metric measuring species segregation as “checkerboard units”, applied to 289 datasets. First, I run null models in which sites are equally likely to be occupied (fixed-equiprobable algorithm). I do this both for the original datasets, and for the same datasets where occurrences are randomised with the species richness distribution fixed (pre-randomised datasets). Second, I run null models that fix site species richness to that observed (fixed-fixed algorithm).ResultsFor real datasets, using the fixed-equiprobable algorithm (sites are equally likely to be colonised), C-score standardised effect size (SES) was positively related to variability in species richness between sites within a dataset. This effect was also found for pre-randomised datasets, indicating that variability in species richness can be exclusively responsible for detection of non-random species co-occurrence. When using the fixed-fixed algorithm (richness is constrained to that of real sites), there was no relationship between SES and variability in species richness. There was also a reverse in the effect direction, with 94% of significant tests indicating a lower C-score than expected for the fixed-equiprobable algorithm, but 98% of significant tests indicating a higher C-score than expected for the fixed-fixed algorithm.DiscussionI speculate that when variation in species richness is high, fewer checkerboard units are possible, regardless of segregation between species. Therefore, use of fixed-equiprobable algorithms in situations where real species richness is highly variable between sites within a dataset will yield significant results, even if species co-occur randomly within the constraints of the species richness distribution. Consequently, use of such tests makes the a priori assumption that high within-dataset variation in species richness indicates non-random species co-occurrence. I recommend using algorithms that explicitly take into account species richness distributions when one wants to eliminate the effect of richness variation in terms of producing significant but spurious positive co-occurrence results. Alternatively, non-null mechanistic models can be created, in which hypothesised species assembly processes must be explicitly stated and tested.

A novel framework for modeling the evolution of cross-scale ecological assembly

Community assembly can be driven by species’ responses to environmental gradients, and interactions within (e.g., competition) and across (e.g., herbivory) clades. These ecological dynamics are mediated by species’ traits, which are in turn shaped by past evolution. As such, identifying the drivers of species assembly is made difficult by the differing temporal and spatial scales of ecological and evolutionary dynamics. Two recent advances have emerged to address the cross-scale challenge of modeling species assembly: phylogenetic generalized linear mixed modeling (PGLMM) and earth observation networks (EONs). PGLMM integrates through time by modeling the evolution of trait-based community assembly, while EONs synthesize across space by placing standardized site-level species occurrence data within their regional context. Here we describe a framework for combining these tools to investigate the drivers of species assembly, and so address three outstanding questions: (1) Does evolution adapt or constrain regional-scale environmental responses? (2) Do evolved responses to past competition minimize or enhance present-day competition? (3) Are species’ cross-clade associations evolutionarily constrained? We provide a conceptual overview of how PGLMM and EONs can be synthesized to answer these questions, and provide exemplar Bayesian PGLMM code. Finally, we describe the capacity of these tools to aid in conservation and natural resource management, including predicting future colonization by rare and invasive species, vulnerable mutualisms, and pest and pathogen outbreaks.

Environmental controls and anthropogenic impacts on deep-sea sponge grounds in the Faroe-Shetland Channel, NE Atlantic: the importance of considering spatial scale to distinguish drivers of change

Determining the scale of anthropogenic impacts is critical in order to understand ecosystem effects of human activities, within the context of changes caused by natural environmental variability. We applied spatial eigenfunction analysis to disentangle effects of anthropogenic drivers from environmental factors on species assembly in the Faroe-Shetland Channel (FSC), in the northeast Atlantic. We found that the species assembly considered here was structured at both small and large spatial scales. Specifically, substrate types, distance to oil wells and pipelines, the presence of objects and demersal fishing (both static and mobile) appeared significant in explaining large spatial scale species assembly structures. Conversely, temperature and variance in temperature shaped the species community across smaller spatial scales. Mobile scavenger species were found in areas impacted by demersal fishing. Oil and gas structures seemed to provide a habitat for a range of species including the commercially important fishes Molva sp. and Sebastes sp. These results demonstrate how the benthic ecosystem in the FSC has been shaped by multiple human activities, at both small and large spatial scales. Only by sampling datasets covering several sites, like in this study, can the effects of anthropogenic activities be separated from natural environmental controls.

How species colonize gaps after soil disturbance in temporary ponds? Implication of species traits

This work aims to review the existing theoretical literature and experiments on plant species colonising gaps after soil disturbance. It attempts to evaluate the various mechanisms by which plants regenerate among the soil openings within the Mediterranean temporary ponds. Intensity and frequency of disturbances are key factors in the response of communities. Knowing the specificity of plant strategies and the species assembly process is important for a better understanding of the impact of soil disturbance on the structure of temporary ponds community, and their mechanisms of resilience. Under the scope of these mechanisms, we will assess the contribution of seed bank by regrowth of buried seeds, vegetative propagules growth via clonal propagation and dispersion of propagules. Soil disturbance has a biotic effect on competition giving a chance to competitively inferior species.