Relationships between climate and phylogenetic community structure of fossil pollen assemblages are not constant during the last deglaciation

Disentangling the influence of environmental drivers on community assembly is important to understand how multiple processes influence biodiversity patterns and can inform understanding of ecological responses to climate change. Phylogenetic Community Structure (PCS) is increasingly used in community assembly studies to incorporate evolutionary perspectives and as a proxy for trait (dis)similarity within communities. Studies often assume a stationary relationship between PCS and climate, though few studies have tested this assumption over long time periods with concurrent community data. We estimated two PCS metrics—Nearest Taxon Index (NTI) and Net Relatedness index (NRI)—of fossil pollen assemblages of Angiosperms in eastern North America over the last 21 ka BP at 1 ka intervals. We analyzed spatiotemporal relationships between PCS and seven climate variables, evaluated the potential impact of deglaciation on PCS, and tested for the stability of climate-PCS relationships through time. The broad scale geographic patterns of PCS remained largely stable across time, with overdispersion tending to be most prominent in the central and southern portion of the study area and clustering dominating at the longitudinal extremes. Most importantly, we found that significant relationships between climate variables and PCS (slope) were not constant as climate changed during the last deglaciation and new ice-free regions were colonized. We also found weak, but significant relationships between both PCS metrics (i.e., NTI and NRI) and climate and time-since-deglaciation that also varied through time. Overall, our results suggest that (1) PCS of fossil Angiosperm assemblages during the last 21ka BP have had largely constant spatial patterns, but (2) temporal variability in the relationships between PCS and climate brings into question their usefulness in predictive modeling of community assembly.

Source range phylogenetic community structure can predict the outcome of avian introductions

Competing phylogenetic models have been proposed to explain the success of species introduced to other communities. Here, we present a study predicting the establishment success of birds introduced to Florida, Hawaii, and New Zealand using several alternative models, considering species' phylogenetic relatedness to source and recipient range taxa, propagule pressure, and traits. We find consistent support for the predictive ability of source region phylogenetic structure. However, we find that the effects of recipient region phylogenetic structure vary in sign and magnitude depending on inclusion of source region phylogenetic structure, delineation of the recipient species pool, and the use of phylogenetic correction in the models. We argue that tests of alternative phylogenetic hypotheses including the both source and recipient community phylogenetic structure, as well as important covariates such as propagule pressure, are likely to be critical for identifying general phylogenetic patterns in introduction success, predicting future invasions, and for stimulating further exploration of the underlying mechanisms of invasibility.

Can trait-based approaches model the resilience of soil microbial communities?

<p>Soil microbial communities (microbiomes) are dynamic, responding continually to their surrounding environment.  These dynamics may relate to changes in the taxonomic/phylogenetic community structure as well as the functional capacity of the entire microbiome. This dynamism makes it challenging to define resilience for such ecosystems. Here, resilient communities are those able to adjust their taxonomic composition under environmental pulse or press stresses to maintain or restore a particular function.  Trait-based models typically assume trade-offs between life cycle strategies because of the resources required to enable different behaviours. An individual trait may be advantageous depending on the environmental conditions at a particular time and location. However, recent experiments addressing resilience in which soils were repeatedly exposed to stress cycles show soils developed the ability to maintain function despite a repeatedly imposed pulse stress. This suggests that a stress tolerance strategy operates in conjunction with other life cycle strategies. Here, we consider conceptual approaches to reconcile these findings – such as the inclusion of additional life strategies to represent further dimensions of soil community function and a community level trait-based approach that represents the dynamics of functional change in trait space. We also consider the challenge, pertinent to resilience modelling, of distinguishing between stress tolerance and the exposure to stress in heterogeneous soil; both aspects will affect the soil microbial community response, yet the latter could erroneously affect stress tolerance parameters in a trait-based model.</p>

Deep-Sea Nematodes of the Mozambique Channel: Evidence of Random Community Assembly Dynamics in Seep Sediments

Cold seeps occur globally in areas where gases escape from the seafloor, occasionally resulting in the formation of topographic depressions (pockmarks), characterised by unique physicochemical conditions such as anoxic and sulphuric sediments. Free-living marine nematodes tend to dominate the meiofaunal component in such environments, often occurring at extremely high densities and low richness; the mechanisms defining community assembly in areas of fluid seepage, however, have received little attention. Here we focus on a low-activity pockmark at 789 m in the Mozambique Channel (MC). We assessed the diversity, co-occurrence patterns and phylogenetic community structure of nematodes at this bathyal site to that of a nearby reference area as well as abyssal sediments using metabarcoding. In addition, we compared our molecularly-derived diversity estimates to replicate samples identified morphologically. Overall, nematode Amplicon Sequence Variants (ASVs) and generic richness were similar between Pockmark and Abyssal sediments, but lower compared to the Reference area. Although more than half the genera were shared, over 80% of ASVs were unique within each area and even within each replicate core. Even though both methodologies differentiated the Pockmark from the Reference and Abyssal sites, there was little overlap between the molecularly and morphologically identified taxa, highlighting the deficit of reference sequences for deep-sea nematodes in public databases. Phylogenetic community structure at higher taxonomic levels was clustered and did not differ between the three areas yet analysis within three shared and dominant genera (Acantholaimus, Desmoscolex, Halalaimus), revealed randomness with respect to phylogeny as well as co-occurrence which was exclusive to the Pockmark area. These patterns point to the influence of neutral dynamics at this locality resulting from the stochastic sampling of early colonizing taxa, the successional stage at sampling and/or the functional redundancy within the investigated genera.

Relatedness and the composition of communities over time: Evaluating phylogenetic community structure in the late Cenozoic record of bivalves

Understanding the mechanisms that prevent or promote the coexistence of taxa at local scales is critical to understanding how biodiversity is maintained. Competitive exclusion and environmental filtering are two processes thought to limit which taxa become established in a community. However, determining the relative importance of the two processes is a complex task, especially when the critical initial stages of colonization cannot be directly observed. Here, we explore the use of phylogenetic community structure for identifying filtering mechanisms in a fossil community. We integrated a time-calibrated molecular phylogeny of bivalve genera with a spatial dataset of late Cenozoic bivalves from the Pacific coast of North America to characterize how the community that was present in the semirestricted San Joaquin Basin (SJB) embayment of present-day California was phylogenetically structured. We employed phylogenetic distance-based metrics across six time bins spanning 27–2.5 Ma and found no evidence of significant clustering or evenness in the SJB community when compared with communities randomly assembled from the regional source pool. Additionally, we found that new colonizers into the SJB were not significantly more or less closely related to native taxa than expected by chance. These findings suggest that neither competitive exclusion nor environmental filtering were overwhelmingly influential factors shaping the composition of the SJB community over time. We further discuss interpretations of these patterns in light of current understandings in community phylogenetics and reiterate the critical role historical perspectives play in how community assembly rules are assessed.

Relationships between climate and phylogenetic community structure of fossil pollen assemblages are not constant during the last deglaciation

Disentangling the influence of environmental drivers on community assembly is important to understand how multiple processes influence biodiversity patterns and can inform understanding of ecological responses to climate change. Phylogenetic Community Structure (PCS) is increasingly used in community assembly studies to incorporate evolutionary perspectives and as a proxy for trait (dis)similarity within communities. Studies often assume a stationary relationship between PCS and climate, though few if any studies have tested this assumption over long time periods with concurrent community data. We estimated Nearest Taxon Index (NTI) and Net Relatedness index (NRI), two PCS metrics, of fossil pollen assemblages of angiosperms in eastern North America data over the last 21 ka BP at 1ka intervals. We analyzed spatiotemporal relationships between PCS and seven climate variables, evaluated the potential impact of deglaciation on PCS, and tested for the stability of climate-PCS relationships. The broad scale patterns of PCS, with overdispersion increasing towards the southern and eastern parts of the study area, remained largely stable across time. Most importantly, we found that significant relationships between climate variables and PCS (slope) were unstable as climate changed during the last deglaciation and new ice-free regions were colonized. We also found weak, but significant, relationships between both PCS metrics (i.e., NTI and NRI) and climate and time-since-deglaciation, which were stable even though the baselines (intercepts) changed through time. Overall, our results suggest that (1) PCS of fossil Angiosperm assemblages during the last 21ka BP have had predictable spatial patterns, but (2) the instability in the relationships between PCS and climate brings into question their usefulness in predictive modeling of community assembly.

Community Assembly as the Basis for Species Selection for Tropical Forest Restoration in Global Change Scenario

Background Tropical forests hold high biodiversity, which challenges the selection of species for forest restoration. For a site-specific restoration is required the understanding of the main influences ruling the assemblages. We aimed to answer three questions. 1) how do environmental variables influence taxonomic, phylogenetic diversities, and the phylogenetic structure in the of Rio Doce Basin (TFRD)? 2) How do environmental variables, phylogenetic structure and the main types of seed dispersal relate to each other? 3) Which information of the TFRD assemblages can be used for ecological restoration and conservation in global change scenario? We used 78 sites with their checklists to calculate taxonomic, and phylogenetic diversities, phylogenetic structures, and dispersal proportions. Then, we related the diversities of the sites to their bioclimatic variables and built GLM models.Results Species richness was influenced negatively by water excess duration, by water deficit duration, and positively by maximum temperature, and temperature seasonality. Water regime drives diversity and phylogenetic community structure in the TFRD more than other variables. Annual precipitation and maximum temperature presented the clearer influences on diversity and phylogenetic structure. Zoochory was positively, and anemochory, autochory were negatively related to sesMPD. Conclusions By choosing the lineages with high fitness for each site, the functioning and the stability of ecosystems should increase. The addition of species with anemochory and autochory increases functional and phylogenetic diversity in areas with extreme water excess or water deficit, important in a global change scenario. A high proportion of zoochory allows the communities to function conserving dispersers, biodiversity, and services.