Spatial patterns of species richness and nestedness in ant assemblages along an elevational gradient in a Mediterranean mountain range

Six groups of ground-dwelling arthropods show different diversity responses along elevational gradients in the Swiss Alps

Elevational gradients along mountain slopes offer opportunities to study key factors shaping species diversity patterns. Several environmental factors change over short distances along the elevational gradient in predictable ways. However, different taxa respond to these factors differently resulting in various proposed models for biodiversity patterns along elevational transects. Using a multi-taxa approach, we investigated the effects of elevation, area, habitat and soil characteristics on species richness, individual abundance and species composition of six groups of ground-dwelling arthropods along four transect lines in the Swiss National Park and its surroundings (Eastern Alps). Spiders, millipedes, centipedes, ants, ground beetles and rove beetles were sampled using standardized methods (pitfall traps, cardboard traps, visual search) in 65 sites spanning an elevational range from 1800 to 2750 m a.s.l.. A total of 14,782 individuals comprising 248 species were collected (86 spider, 74 rove beetle, 34 ground beetle, 21 millipede, 19 centipede and 14 ant species). Linear mixed model-analysis revealed that rarefied species richness in five out of the six arthropod groups was affected by elevation (the quadratic term of elevation provided the best fit in most cases). We found three different patterns (linear decrease in centipedes, low elevation plateau followed by a decrease in ants and rove beetles, and midpoint peak in spiders and millipedes). These patterns were only partially mirrored when considering individual abundance. Elevation influenced species composition in all groups examined. Overall, elevation was the most important factor explaining the diversity patterns, while most local habitat and soil characteristics have little influence on these patterns. Our study supports the importance of using multi-taxa approaches when examining effects of elevational gradients. Considering only a single group may result in misleading findings for overall biodiversity.

Ants of the Palouse Prairie: diversity and species composition in an endangered grassland

Grasslands are globally imperilled ecosystems due to widespread conversion to agriculture and there is a concerted effort to catalogue arthropod diversity in grasslands to guide conservation decisions. The Palouse Prairie is one such endangered grassland; a mid-elevation habitat found in Washington and Idaho, United States. Ants (Formicidae) are useful indicators of biodiversity and historical ecological disturbance, but there has been no structured sampling of ants in the Palouse Prairie. To fill this gap, we employed a rapid inventory sampling approach using pitfall traps to capture peak ant activity in five habitat fragments. We complemented our survey with a systemic review of field studies for the ant species found in Palouse Prairie. Our field inventory yielded 17 ant species across 10 genera and our models estimate the total ant species pool to be 27. The highest ant diversity was found in an actively-managed ecological trust in Latah County, Idaho, suggesting that restoration efforts may increase biodiversity. We also report two rarely-collected ants in the Pacific Northwest and a microgyne that may represent an undescribed species related to Brachymyrmexdepilis. Our score-counting review revealed that grassland ants in Palouse Prairie have rarely been studied previously and that more ant surveys in temperate grasslands have lagged behind sampling efforts of other global biomes.

Mid-elevational Peaks in Diversity of Ground-dwelling Arthropods with High Species Turnover on the Colorado Plateau

Patterns of biodiversity along elevational gradients elucidate how climate shapes biological communities and help predict ecosystem responses to environmental change. Arid elevational gradients are particularly interesting because temperature limitations at high elevations and precipitation limitations at low elevations cause mid-elevation peaks in diversity. Ground-dwelling arthropods form highly diverse communities but few studies document elevational patterns of their full diversity. Here we investigate the elevational patterns of ground-dwelling arthropods in northern Arizona on the Colorado Plateau, an arid and understudied region in the United States. We sampled seven sites along an elevation gradient from 1,566 to 2,688 m corresponding to a difference of 6.5°C average annual temperature and 620 mm average annual precipitation. We captured 16,942 specimens comprising 169 species, mostly ants and beetles, and discovered a new ant species. First- and second-order elevation terms significantly correlated to multiple measures of arthropod α and β diversity. Arthropod abundance, richness, and Shannon-Wiener diversity index peaked at mid-elevations, with functional groups (i.e., omnivores, predators, detritivores, and herbivores) showing similar patterns. Community composition varied significantly across the gradient, correlated with changes in elevation, and was driven by shifts of ants dominating low- to mid-elevations, to beetles dominating high-elevations. Dissimilarity among sites was driven by high species turnover with 59% of species exclusive to a single site, whereas nestedness among sites was low except at the lowest elevation site. High rates of turnover and elevation-dependent communities suggest that ground-dwelling arthropods are highly vulnerable to environmental change, particularly at lower elevations in arid regions.

Ant Communities Resist Even in Small and Isolated Gypsum Habitat Remnants in a Mediterranean Agroecosystem

Natural and seminatural habitat remnants play a crucial ecological role in intensified agroecosystems. Assumptions on the conservation value of small and poorly connected fragments in a hostile matrix come from generalization obtained from a limited number of taxa, mostly plants, and vertebrates. To date, few studies have analyzed the effect of fragmentation on ant communities in Mediterranean agroecosystems, despite the importance of this group of animals on several key ecosystem functions and services. Here, we analyze the effects of fragment area and connectivity on ant communities in gypsum outcrops in a large cereal agroecosystem of Central Spain. Ant communities were described by their species composition, abundance (total number of occurrences), and number of species, standardized both by area (species density), and abundance (species richness). Observed number of species was relatively high in comparison with other studies in the Mediterranean, and we found no effects of fragment characteristics on species density, species richness and species composition, which implies that even small and isolated patches do have a value for ant conservation. Moreover, total number of occurrences were higher for smaller and more isolated fragments. This finding contrasts with the results reported for other taxa in similar gypsum habitats and suggests that certain ant traits and strategies make them particularly resistant to fragmentation and capable to take advantage of small habitat patches. Given the important ecological role played by ants, we recommend the preservation of these small habitat fragments in the management plans of agroecosystems in these drylands, especially in those cases in which intensification of agricultural practices greatly diminish natural habitat availability.

A multimetric approach to evaluate offshore mussel aquaculture effects on the taxonomical and functional diversity of macrobenthic communities

A multimetric approach was used to detect structural, compositional, and functional shifts in the underlying macrobenthic communities of an offshore mussel (Mytilus galloprovincialis) farm in a Portuguese Aquaculture Production Area. Sampling stations distributed inside and outside this area were used to evaluate sediment descriptors and macrobenthic samples collected before (April and September 2010) and after (June and September 2014) the initiation of mussel farming. Sediment fine fraction, organic matter content, and trace element concentrations were found to increase with depth, independently from the mussel farm. Moreover, the structure and composition of the macrobenthic communities were likewise structured by depth. Turnover was the dominant temporal and spatial pattern of beta diversity for all communities. Furthermore, the functional diversity of these communities was unaffected by the mussel farm. These results suggested that an offshore profile allowed hydrodynamic conditions to weaken the impact of mussel farming and highlighted the importance of conducting an integrative multimetric analysis when studying aquaculture impacts on benthic communities.