Whether niche processes, like environmental filtering, or neutral processes, like dispersal limitation, are the primary forces driving community assembly is a central question in ecology. Here, we use a natural experimental system of isolated tree “islands” to test whether environment or geography primarily structures fungal community composition at fine spatial scales. This system consists of isolated pairs of two distantly related, congeneric pine trees established at varying distances from each other and the forest edge, allowing us to disentangle the effects of geographic distance vs. host and edaphic environment on associated fungal communities. We identified fungal community composition with Illumina sequencing of
Benthic microalgae (
- NSF-PAR ID:
- 10246690
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Phycology
- Volume:
- 52
- Issue:
- 5
- ISSN:
- 0022-3646
- Format(s):
- Medium: X Size: p. 827-839
- Size(s):
- ["p. 827-839"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract ITS amplicons, measured all relevant environmental parameters for each tree—including tree age, size and soil chemistry—and calculated geographic distances from each tree to all others and to the nearest forest edge. We applied generalized dissimilarity modelling to test whether total and ectomycorrhizal fungal (EMF ) communities were primarily structured by geographic or environmental filtering. Our results provide strong evidence that as in many other organisms, niche and neutral processes both contribute significantly to turnover in community composition in fungi, but environmental filtering plays the dominant role in structuring both free‐living and symbiotic fungal communities at fine spatial scales. In our study system, we foundpH and organic matter primarily drive environmental filtering in total soil fungal communities and thatpH and cation exchange capacity—and, surprisingly, not host species—were the largest factors affectingEMF community composition. These findings support an emerging paradigm thatpH may play a central role in the assembly of all soil‐mediated systems. -
more » « less
Abstract Ecological communities are structured by a combination of local processes like habitat filtering and species interactions, and regional forces driven by the dispersal of organisms between localities on a landscape. Previous studies suggest that the position of local communities within a dispersal network can greatly influence the relative influence of these two sets of processes on community assembly. However, the majority of previous investigations have used models or inferences based on observational data to investigate these hypotheses, while experiments directly addressing this question have been rare.
We experimentally investigated the relative influence of local and regional processes in structuring benthic invertebrate communities using artificial streams. We manipulated three factors—source pool for the macroinvertebrate community (headwater vs. mainstem) as a surrogate of network location, habitat complexity (high vs. low) in the flume, and dispersal (high vs. low)—and followed changes in macroinvertebrate community structure for 8 weeks.
Previous research suggests that because headwater (
HW ) streams are isolated within river networks,HW s are less influenced by regional processes relative to more well‐connected mainstems (MS s). We therefore predicted (i) that flumes colonised from aHW source community would respond more strongly to our dispersal treatment than those colonised byMS communities becauseMS were already largely structured through dispersal‐driven processes, and (ii) that bothHW andMS communities would respond to manipulations of local habitat, indicating that responses to the dispersal treatment were a direct result of dispersal driven dynamics rather than specific affinity for conditions in the flumes.Both of our predictions were strongly supported by the results of the experiment. For flumes with
HW source pools, the high dispersal treatment had significantly higher diversity than low dispersal flumes. However, this difference only occurred in flumes withHW source pools and did not occur in flumes withMS sources. There was also strong evidence of community composition inHW flumes shifting significantly towards the macroinvertebrate composition in our experimental dispersal treatment. The major effect of experimental dispersal was to introduce new species in fairly low abundances as would be expected from dispersal via drift over a relatively short time. BothMS andHW colonised flumes showed highly significant signals of habitat filtering, though the influence of specific habitat differed between the source types.These results support the hypothesis that dispersal driven processes are a more important structuring force in well‐connected areas of networks by experimentally demonstrating the responsiveness of previously isolated communities to experimentally induced dispersal. They also demonstrate that this responsiveness is not due to an inherent difference in habitat affinity since source communities from both
HW s andMS s responded to manipulation of habitat variables. This experiment only simulated one type of dispersal process in streams—drifting—and did not include simulated dispersal from other sources, nor did it include population dynamics given the relatively short duration of the experiment. Nevertheless, the sensitivity of previously isolated communities to one type of simulated dispersal is a powerful indication of the mechanisms that structure these systems. -
more » « less
Abstract The study of diversity has become increasingly sophisticated, including the use of measures of phylogenetic diversity.
We calculate the spatial variation in species richness, taxonomic beta diversity, and alpha and beta phylogenetic diversity (
PD α andPD β , respectively) of Atlantic Forest harvestman communities using a data set containing 556 species from 68 sites, distributed in 12 Brazilian states.We compare the congruence of phylogenetic and taxonomic diversity patterns, and also compare
PD α with null model expectations, to check for phylogenetic clustering or overdispersion in communities.Species richness and
PD α are correlated, peaking in southern and south‐eastern coastal sites and decreasing towards the interior and towards the north‐east.PD α in north‐eastern sites was higher than expected, while a clustered phylogenetic pattern characterised most other sites.Communities in the southern and south‐eastern regions were dominated by species from the large family Gonyleptidae, presenting a high richness and a low
PD α . As the dominance of Gonyleptidae decreased towards the north, where local communities have fewer species, but a higherPD α , they contain representatives of other families. The beta diversity was more sensitive to the compositional changes involving closely related Gonyleptidae species, whilePD β is more influenced by deeper phylogenetic compositional changes, between more distant lineages.Phylogenetic diversity may be of special importance to assess the conservation value of distantly related lineages. These species‐poor groups are less likely to influence taxonomic‐based diversity analyses, but their importance for conservation arises from their phylogenetic distinctiveness, captured by
PD α andPD β measures. -
more » « less
Premise At the intersection of ecology and evolutionary biology, community phylogenetics can provide insights into overarching biodiversity patterns, particularly in remote and understudied ecosystems. To understand community assembly of the high alpine flora in the Sawtooth National Forest,
USA , we analyzed phylogenetic structure within and between nine summit communities.Methods We used high‐throughput sequencing to supplement existing data and infer a nearly completely sampled community phylogeny of the alpine vascular flora. We calculated mean nearest taxon distance (
MNTD ) and mean pairwise distance (MPD ) to quantify phylogenetic divergence within summits, and assessed whether maximum elevation explains phylogenetic structure. To evaluate similarities between summits, we quantified phylogenetic turnover, taking into consideration microhabitats (talus vs. meadows).Results We found different patterns of community phylogenetic structure within the six most species‐rich orders, but across all vascular plants phylogenetic structure was largely not different from random. There was a significant negative correlation between elevation and tree‐wide phylogenetic diversity (
MPD ) within summits: overdispersion degraded as elevation increased. Between summits, we found high phylogenetic turnover driven by greater niche heterogeneity on summits with alpine meadows.Conclusions Our results provide further evidence that stochastic processes may also play an important role in the assembly of vascular plant communities in high alpine habitats at regional scales. However, order‐specific patterns suggest that adaptations are still important for assembly of specific sectors of the plant tree of life. Further studies quantifying functional diversity will be important in disentangling the interplay of eco‐evolutionary processes that likely shape broad community phylogenetic patterns in extreme environments.
-
more » « less
Abstract Establishing diverse mycorrhizal fungal communities is considered important for forest recovery, yet mycorrhizae may have complex effects on tree growth depending on the composition of fungal species present. In an effort to understand the role of mycorrhizal fungi community in forest restoration in southern Costa Rica, we sampled the arbuscular mycorrhizal fungal (
AMF ) community across eight sites that were planted with the same species (Inga edulis, Erythrina poeppigiana, Terminalia amazonia, andVochysia guatemalensis ) but varied twofold to fourfold in overall tree growth rates. TheAMF community was measured in multiple ways: as percent colonization of host tree roots, byDNA isolation of the fungal species associated with the roots, and through spore density, volume, and identity in both the wet and dry seasons. Consistent with prior tropical restoration research, the majority of fungal species belonged to the genusGlomus and genusAcaulospora , accounting for more than half of the species and relative abundance found on trees roots and over 95% of spore density across all sites. GreaterAMF diversity correlated with lower soil organic matter, carbon, and nitrogen concentrations and longer durations of prior pasture use across sites. Contrary to previous literature findings,AMF species diversity and spore densities were inversely related to tree growth, which may have arisen from trees facultatively increasing their associations withAMF in lower soil fertility sites. Changes toAMF community composition also may have led to variation in disturbance susceptibility, host tree nutrient acquisition, and tree growth. These results highlight the potential importance of fungal–tree–soil interactions in forest recovery and suggest that fungal community dynamics could have important implications for tree growth in disturbed soils.
