Habitat loss and fragmentation are leading causes of species declines, driven in part by reduced dispersal. Isolating the effects of fragmentation on dispersal, however, is daunting because the consequences of fragmentation are typically intertwined, such as reduced connectivity and increased prevalence of edge effects. We used a large‐scale landscape experiment to separate consequences of fragmentation on seed dispersal, considering both distance and direction of local dispersal. We evaluated seed dispersal for five wind‐ or gravity‐dispersed, herbaceous plant species that were planted at different distances from habitat edges, within fragments that varied in their connectivity and shape (edge‐to‐area ratio). Dispersal distance was affected by proximity and direction relative to the nearest edge. For four of five species, dispersal distances were greater further from habitat edges and when seeds dispersed in the direction of the nearest edge. Connectivity and patch edge‐to‐area ratio had minimal effects on local dispersal. Our findings illustrate how some, but not all, landscape changes associated with fragmentation can affect the key population process of seed dispersal.
Habitat fragmentation is a leading threat to biodiversity, yet the impacts of fragmentation on most taxa, let alone interactions among those taxa, remain largely unknown.
We studied how three consequences of fragmentation—reduced patch connectivity, altered patch shape, and edge proximity—impact plant-dwelling mite communities and mite-plant-fungus interactions within a large-scale habitat fragmentation experiment.
We sampled mite communities from the leaves of
Habitat edges influenced the abundance and richness of leaf-dwelling mites; plants closer to the edge had higher mite abundance and species richness. Likewise, hyphal counts were higher on leaves near patch edges. Despite both mite and fungal abundance being higher at patch edges, leaf hyphal counts were not impacted by mite abundance on those leaves. Neither patch shape nor connectivity influenced mite abundance, mite species richness, or the influence of mites on leaf surface fungal abundance.
Our results suggest that mites and foliar fungi may be independently affected by edge-structured environmental gradients, like temperature, rather than trophic effects. We demonstrate that large-scale habitat fragmentation and particularly edge effects can have impacts on multiple levels of microscopic communities, even in the absence of cascading trophic effects.
- NSF-PAR ID:
- 10373699
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Landscape Ecology
- Volume:
- 37
- Issue:
- 12
- ISSN:
- 0921-2973
- Page Range / eLocation ID:
- p. 3029-3041
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract The structure of local ecological communities is thought to be determined by a series of hierarchical abiotic and biotic filters which select for or against species based on their traits. Many human impacts, like fragmentation, serve to alter environmental conditions across a range of spatial scales and may impact trait–environment interactions.
We examined the effects of environmental variation associated with habitat fragmentation of seagrass habitat measured from microhabitat to landscape scales in controlling the taxonomic and trait‐based community structure of benthic fauna.
We measured patterns in species abundance and biomass of seagrass epifauna and infauna sampled using sediment cores from 86 sites (across 21 meadows) in Back Sound, North Carolina, USA. We related local faunal community structure to environmental variation measured at three spatial scales (microhabitat, patch and landscape). Additionally, we tested the value of species traits in predicting species‐specific responses to habitat fragmentation across scales.
While univariate measures of faunal communities (i.e. total density, biomass and species richness) were positively related to microhabitat‐scale seagrass biomass only, overall community structure was predicted by environmental variation at the microhabitat, patch (i.e. patch size) and landscape (i.e. number of patches, landscape seagrass area) scales. Furthermore, fourth‐corner analysis revealed that species traits explained as much variation in organismal densities as species identity. For example, species with planktonic‐dispersing larvae and deposit‐feeding trophic modes were more abundant in contiguous, high seagrass cover landscapes while suspension feeders favoured more fragmented landscapes.
We present quantitative evidence supporting hierarchal models of community assembly which predict that interactions between species traits and environmental variation across scales ultimately drive local community composition. Variable responses of individual traits to multiple environmental variables suggest that community assembly processes that act on species via traits related to dispersal, mobility and trophic mode will be altered under habitat fragmentation. Additionally, with increasing global temperatures, the tropical seagrass
Halodule wrightii is predicted to replace the temperateZostera marina as the dominate seagrass in our study region, therefore potentially favouring species with planktonic‐dispersing larva and weakening the strength of environmental control on community assembly. -
more » « less
Abstract The plant microbiome can affect host function in many ways and characterizing the ecological factors that shape endophytic (microbes living inside host plant tissues) community diversity is a key step in understanding the impacts of environmental change on these communities. Phylogenetic relatedness among members of a community offers a way of quantifying phylogenetic diversity of a community and can provide insight into the ecological factors that shape endophyte microbiomes. We examined the effects of experimental nutrient addition and herbivory exclusion on the phylogenetic diversity of foliar fungal endophyte communities of the grass species
Andropogon gerardii at four sites in the Great Plains of the central USA. Using amplicon sequencing, we characterized the effects of fertilization and herbivory on fungal community phylogenetic diversity at spatial scales that spanned within‐host to between sites across the Great Plains. Despite increasing fungal diversity and richness, at larger spatial scales, fungal microbiomes were composed of taxa showing random phylogenetic associations. Phylogenetic diversity did not differ systematically when summed across increasing spatial scales from a few meters within plots to hundreds of kilometers among sites. We observed substantial shifts in composition across sites, demonstrating distinct but similarly diverse fungal communities were maintained within sites across the region. In contrast, at the scale of within leaves, fungal communities tended to be comprised of closely related taxa regardless of the environment, but there were no shifts in phylogenetic composition among communities. We also found that nutrient addition (fertilization) and herbivory have varying effects at different sites. These results suggest that the direction and magnitude of the outcomes of environmental modifications likely depend on the spatial scale considered, and can also be constrained by regional site differences in microbial diversity and composition. -
more » « less
Abstract Shelter building caterpillars act as ecosystem engineers by creating and maintaining leaf shelters, which are then colonized by other arthropods. Foliage quality has been shown to influence initial colonization by shelter-building caterpillars. However, the effects of plant quality on the interactions between ecosystem engineers and their communities have yet to be studied at the whole plant level. We examined how leaf tying caterpillars, as ecosystem engineers, impact arthropod communities on
Quercus alba (white oak), and the modifying effect of foliage quality on these interactions. We removed all leaf tying caterpillars and leaf ties on 35Q. alba saplings during the season when leaf tying caterpillars were active (June–September), and compared these leaf tie removal trees to 35 control trees whose leaf ties were left intact. Removal of these ecosystem engineers had no impact on overall arthropod species richness, but reduced species diversity, and overall arthropod abundance and that of most guilds, and changed the structure of the arthropod community as the season progressed. There was an increase in plant-level species richness with increasing number of leaf ties, consistent with Habitat Diversity Hypothesis. In turn, total arthropod density, and that of both leaf tying caterpillars and free-feeding caterpillars were affected by foliar tannin and nitrogen concentrations, and leaf water content. The engineering effect was greatest on low quality plants, consistent with the Stress-Gradient Hypothesis. Our results demonstrate that interactions between ecosystem engineering and plant quality together determine community structure of arthropods onQ. alba in Missouri. -
more » « less
Summary Foliar fungal endophytes are one of the most diverse guilds of symbiotic fungi found in the photosynthetic tissues of every plant lineage, but it is unclear how plant environments and leaf resource availability shape their diversity.
We explored correlations between leaf nutrient availability and endophyte diversity among
Pinus muricata andVaccinium ovatum plants growing across a soil nutrient gradient spanning a series of coastal terraces in Mendocino, California.Endophyte richness decreased in plants with higher leaf nitrogen‐to‐phosphorus ratios for both host species, but increased with sodium, which may be toxic to fungi at high concentrations. Isolation frequency, a proxy of fungal biomass, was not significantly predicted by any of the same leaf constituents in the two plant species.
We propose that stressed plants can exhibit both low foliar nutrients or high levels of toxic compounds, and that both of these stress responses predict endophyte species richness. Stressful conditions that limit growth of fungi may increase their diversity due to the suppression of otherwise dominating species. Differences between the host species in their endophyte communities may be explained by host specificity, leaf phenology, or microclimates.
