Turning back the tide? Local-scale impacts of climate change may have positive effects by restoring natural riverine habitat and reducing invasive fish density

1. Global biodiversity is increasingly threatened by habitat loss, climate change, and biological invasion. However, predictions of impacts on native fauna are hampered by an inadequate knowledge of how these factors interact and how climate change will affect the distribution, abundance, and behaviour of both native and invasive species, not least as most predictions are based on the long-term effects of temperature alone.
2. Here, we present a case study illustrating how local-scale climate change impacts (increased temperature, reduced rainfall, shifts in peak rainfall) affected the hydrology of a channelised lowland European river (reduced flow, reduction in flood events, increased siltation, macrophyte growth), allowing native fish species to recolonise the bankside zone and reducing the density of invasive round goby Neogobius melanostomus by removing its preferred habitat.
3. While most studies predict long-term negative impacts on global fish populations, some suggest potential direct and indirect benefits at a local scale. We are of the opinion that, at a local scale, climate change impacts on fish will be more nuanced and complex than long-term predictions suggest, resulting in both positive and negative effects, with consolation prizes in the face of larger losses. While impacts on fish will differ between regions and/or continents, depending on the specific impacts of climate change, identification of positive effects will be essential in clarifying long-range forecasts and identifying management procedures for mitigating overall negative impacts.

     

Evaluating the link between predation and pest control services in the mite world

1. Pest regulation by natural enemies has a strong potential to reduce the use of synthetic pesticides in agroecosystems. However, the effective role of predation as an ecosystem service remains largely speculative, especially with minute organisms such as mites.
2. Predatory mites are natural enemies for ectoparasites in livestock farms. We tested for an ecosystem level control of the poultry pest Dermanyssus gallinae by other mites naturally present in manure in poultry farms and investigated differences among farming practices (conventional, free‐range, and organic).
3. We used a multiscale approach involving (a) in vitro behavioral predation experiments, (b) arthropod inventories in henhouses with airborne DNA, and (c) a statistical model of covariations in mite abundances comparing farming practices.
4. Behavioral experiments revealed that three mites are prone to feed on D. gallinae. Accordingly, we observed covariations between the pest and these three taxa only, in airborne DNA at the henhouse level, and in mites sampled from manure. In most situations, covariations in abundances were high in magnitude and their sign was positive.
5. Predation on a pest happens naturally in livestock farms due to predatory mites. However, the complex dynamics of mite trophic network prevents the emergence of a consistent assemblage‐level signal of predation. Based on these results, we suggest perspectives for mite‐based pest control and warn against any possible disruption of ignored services through the application of veterinary drugs or pesticides.

     

Linking life history strategies and historical baseline information shows effects of altered flow regimes and impoundments on freshwater mussel assemblages

1. Human impacts on aquatic ecosystems are causing shifts in the composition and distribution of species, leading to subsequent changes in community structure. However, these changes may not be fully realised because of inadequate baseline information. In Texas, such baseline information is generally lacking for cryptic aquatic species such as unionid mussels, which will be likely to impede identification of impacted populations, potential causal factors, and the setting or achieving of management goals.
2. The Navasota River, located in central Texas, is an exception, having been comprehensively surveyed more than 40 years ago, prior to large-scale impoundment of this system. Hierarchical cluster analysis, nonmetric multidimensional scaling, and fuzzy set ordination were performed to compare assemblage structure from the 1975 survey to that of a recent survey in 2016 at similar sampling locations.
3. Comparing sites based on the presence–absence of mussel species, we found no significant differences between the number of taxa and species present; however, we did find significant filtering of mussel life history strategies. Specifically, prior to impoundment, we found that mussel assemblages were filtered based on longitudinal patterns in life history strategy from taxa that are adapted to disturbed habitats to those favoured in more stable habitats with low environmental variation.
4. However, following large-scale impoundment after 1975, we saw a shift in the hydrologic regime towards consistent, homogenised flows and a shift in assemblage structure towards equilibrium species. This shift appears to represent a discontinuity, wherein river impoundment alters physical parameters of the hydrologic regime and these changes in turn modify biotic patterns and processes.
5. Our results provide another example of how large dams can restructure mussel assemblages, highlight the importance of incorporating reference or baseline conditions wherever possible when evaluating the conservation status of aquatic biota, and provide further evidence for the use of life history theory and the serial discontinuity concept in predicting the consequences of flow alteration and river impoundment.

     

Effects of global change on bird and beetle populations in boreal forest landscape: An assemblage dissimilarity analysis

Aim

Despite an increasing number of studies highlighting the impacts of climate change on boreal species, the main factors that will drive changes in species assemblages remain ambiguous. We study how species community composition would change following anthropogenic and natural disturbances. We determine the main drivers of assemblage dissimilarity for bird and beetle communities.

Location

Côte-Nord, Québec, Canada.

Methods

We quantify two climate-induced pathways based on direct and indirect effects on species occurrence under different forest harvest management scenarios. The direct climate effects illustrate the impact of climate variables while the indirect effects are reflected through habitat-based climate change. We develop empirical models to predict the distribution of 127 and 108 species under climate-habitat and habitat-only models, respectively, over the next century. We analyse the regional and the latitudinal species assemblage dissimilarity by decomposing it into balanced variation in species occupancy and occurrence and occupancy and occurrence gradient.

Results

Both pathways increased dissimilarity in species assemblage. At the regional scale, both effects have an impact on decreasing the number of winning species. Yet, responses are much larger in magnitude under mixed climate effects. Regional assemblage dissimilarity reached 0.77 and 0.69 under mixed effects versus 0.09 and 0.10 under indirect effects for beetles and birds, respectively, between RCP8.5 and baseline climate scenarios when considering forest harvesting. Latitudinally, assemblage dissimilarity increased following the climate conditions pattern.

Main conclusions

The two pathways are complementary and alter biodiversity, mainly caused by species turnover. Yet, responses are much larger in magnitude under mixed climate effects. Therefore, inclusion of climatic variables considers aspects other than just those related to forest landscapes, such as life cycles of animal species. Moreover, we expect differences in occupancy between the two studied taxa. This could indicate the potential range of change in boreal species concerning novel environmental conditions.     

Engineering novel habitats on urban infrastructure to increase intertidal biodiversity

Urbanization replaces natural shorelines with built infrastructure, seriously impacting species living on these “new” shores. Understanding the ecology of developed shorelines and reducing the consequences of urban development to fauna and flora cannot advance by simply documenting changes to diversity. It needs a robust experimental programme to develop ways in which biodiversity can be sustained in urbanized environments. There have, however, been few such experiments despite wholesale changes to shorelines in urbanized areas. Seawalls––the most extensive artificial infrastructure––are generally featureless, vertical habitats that support reduced levels of local biodiversity. Here, a mimic of an important habitat on natural rocky shores (rock-pools) was experimentally added to a seawall and its impact on diversity assessed. The mimics created shaded vertical substratum and pools that retained water during low tide. These novel habitats increased diversity of foliose algae and sessile and mobile animals, especially higher on the shore. Many species that are generally confined to lowshore levels, expanded their distribution over a greater tidal range. In fact, there were more species in the constructed pools than in natural pools of similar size on nearby shores. There was less effect on the abundances of mobile animals, which may be due to the limited time available for recruitment, or because these structures did not provide appropriate habitat. With increasing anthropogenic intrusion into natural areas and concomitant loss of species, it is essential to learn how to build urban infrastructure that can maintain or enhance biodiversity while meeting societal and engineering criteria. Success requires melding engineering skills and ecological understanding. This paper demonstrates one cost-effective way of addressing this important issue for urban infrastructure affecting nearshore habitats. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Littoral benthos of a Victorian lake and its outlet stream: Spatial and temporal variation

Abstract There have been few comparative studies of the fauna in the two major types of freshwater systems, lakes and streams, in the one locality. This study compared the faunal assemblages at two times of the year (summer and winter) on stones in three locations: the littoral zone of two shores in Lake Purrumbete (one wave-exposed and one sheltered) and riffles in the Curdies River, which flows out of the lake. The lake fauna was dominated by crustaceans, gastropods and planarians, whereas the stream fauna was dominated by insects. The most abundant lake taxa were also present, but much less abundant, in the stream. The total number of species and individuals and densities of some common species varied between the three locations and between seasons. However, no consistent pattern reflecting a difference between the two lake shores was evident. Interpretation of MDS ordinations of the lake fauna was dependent on the data standardizations applied, with increased separation of the season-location combinations when species were standardized to equal total abundances; the seasonal difference was always greatest for the exposed (cliff) shore. In contrast, MDS on the stream fauna showed seasonal differences under all standardizations. This was consistent with the high seasonal turnover of species in the stream compared with the lake. These results demonstrate that, even within a local area with similar geology and connected water bodies, lake and stream fauna from the same substratum (stones) can be markedly different. Taxa that occurred in both were more abundant in the lake, whereas seasonal differences in abundance were much greater in the stream.     

Sampling local ant diversities and the importance of trait analyses

Ants are an incredibly diverse and ubiquitous group of invertebrates in most terrestrial ecosystems. Although extensively sampled, the majority of ant inventories do not evaluate the effect of different sampling techniques in capturing nontraditional metrics of diversity. We aimed to quantify TD (taxonomic) and FD (functional) diversities for a local ant assemblage by integrating metrics and evaluating complementarity of pitfall traps and Winkler extractors for the leaf litter versus epigeic ant faunas and to determine the effect of sampling techniques on functional composition (community-weighted means of 11 morphological traits) and functional diversity (multi-trait morphospace measured with three different metrics). We sampled the local community in an Atlantic Forest fragment using week-long pitfall traps and 1m² leaf litter samples submitted to Winkler extractors and quantified the contribution on the technique to uniquely capture the ant morphospace by applying a new index (PWindex). Although ant TD overlapped, FD was significantly affected by the sampling technique. By controlling for TD effects, the community collected by each technique was differentially structured. Higher TD did not translate into wider morphospace for Winklers. Pitfalls recovered more functionally overdispersed assemblages. Pitfalls and Winklers overlapped in the sampling of the overall community, but each sampling method contributed with a unique spectrum to the ant morphospace. Our results suggest the importance of incorporating FD metrics in local ant inventories and the importance of sampling techniques when measuring the magnitude of FD and community structure. Our PWindex further illuminates sampling effects for ant assemblages. Abstract in Portuguese & Spanish is available with online material.     

Compartmentalized organization of ecological niche occupation in insular invertebrate communities

Understanding the mechanisms of species distribution within ecosystems is a fundamental question of ecological research. The current worldwide changes and loss of habitats associated with a decline in species richness render this topic a key element for developing mitigation strategies. Ecological niche theory is a widely accepted concept to describe species distribution along environmental gradients where each taxon occupies its own distinct set of environmental parameters, that is, its niche. Niche occupation has been described in empirical studies for different closely related taxa, like ant, ungulate, or skink species, just to name a few. However, how species assemblages of whole ecosystems across multiple taxa are structured and organized has not been investigated thoroughly, although considering all taxa of a community would be essential when analyzing realized niches. Here, we investigated the organization of niche occupation and species distribution for the whole ground‐associated invertebrate community of small tropical insular ecosystems. By correlating environmental conditions with species occurrences using partial canonical correspondence analysis (pCCA), we demonstrated that the ground‐associated invertebrate community does not spread evenly across the overall niche space, but instead is compartmentalized in four distinct clusters: crustacean and gastropod taxa occurred in one cluster, attributable to the beach habitat, whereas hexapods and spider taxa occurred in three distinct inland clusters, attributable to distinct inland habitats, that is, grassland, open forest, and dense forest. Within the clusters, co‐occurrence pattern analysis suggested only a few negative interactions between the different taxa. By studying ground‐associated insular invertebrate communities, we have shown that species distribution and niche occupation can be, similar to food webs, organized in a compartmentalized way. The compartmentalization of the niche space might thereby be a mechanism to increase ecosystem resilience, as disturbances cascade more slowly throughout the ecosystem.     

Food Limitation Affects Algivory and Grazer Performance for New Zealand Stream Macroinvertebrates

We studied herbivory and grazer performance (i.e., fitness correlates) for the hydrobiid snail Potamopyrgus antipodarum, the leptophlebiid mayfly Deleatidium spp., and the conoesucid caddisfly Pycnocentrodes aeris, common, co-occurring algivores in many New Zealand streams. Grazing effects and costs of coexisting differed among these taxa reared at ambient densities in different combinations in microcosms with algal food conditions (on clay tiles) characteristic of heavily grazed streams. The prostrate diatoms Staurosirella leptostauron, Cymbella novazealandia, and Achnanthidium minutissimum were the dominant algal species on pre- and post-grazed tiles. The relative abundance of erect physiognomic forms, dominated by Synedra ulna and Fragilaria vaucheriae, were 2–3× higher in ungrazed controls and in snail alone treatments than in other grazer treatments. The green filamentous algae Mougeotia sp. and Stigeoclonium lubricum, and the cyanophyte Merismopedia glauca were present only in ungrazed controls. Grazers significantly reduced algal community biomass in treatments by 26–52% relative to controls, except snails alone. Snails (15–30%) burrowed into surrounding sand substrates, dampening their grazing impact on tiles. Caddisflies were more effective than mayflies or snails at removing algae because of higher foraging rates, a larger body size, and an abrasive sand-grained case. Algal biomass reductions did not affect grazer growth. However, pre-pupation rates of caddisflies and emergence rates of subimago mayflies were significantly higher in caddisfly-alone and mayfly-alone treatments, respectively, than in combined-species treatments. These results imply that a limited periphytic food supply ( < 0.3 mg AFDM cm⁻²) even over a relatively brief period ( ≤ 16 d) may have population-scale consequences for co-existing P. aeris and Deleatidium spp.