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"Samways, Michael J"
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Insect-flower interaction networks vary among endemic pollinator taxa over an elevation gradient
Interaction networks are sensitive to elevation gradients through changes in local distribution of interacting partners. Here, we use plant-pollinator interaction network metrics to assess the effect of elevation on flowers and flower-visiting insect assemblages on a sentinel mountain used for monitoring climate change in the flower- and insect-rich Cape Floristic Region. We also use these interaction metrics to explain the effect of environmental factors on the interaction networks. We did this over four vegetation zones <1640m asl, as determined by former botanical studies. Overall, bees were the dominant flower visitors, followed by monkey beetles, and far behind were wasps and flies. The middle elevation zone (650-744 m a.s.l), which is also an ecotone between two distinct botanical zones, had the highest species richness and abundance of interacting plants and insects. Interaction frequency and size of network were also greatest in the middle zone, as were network diversity, generality, and linkage density, while lowest in the peak zone. In sum, there was distinct elevation zoning of flower-visiting insects. The greatest zonal change was between species at the middle compared with peak zone. Large-sized monkey beetles, bees and flies characterized the unique assemblage in the peak zone (1576-1640 m a.s.l.). The insect zonation tracked that of plant assemblages, with air temperature (lapse rate) being the primary driver of bee distribution, with lowest levels in the peak zone. In contrast, beetle distribution was driven mostly by flower assemblages as well as air temperature. In turn, wasp and fly interaction networks were not affected by any of the measured environmental variables. We conclude that increased elevation stress from reduced temperatures, changing abiotic weather conditions (e.g. strong winds at high elevations),and decline in flowering plant composition causes breakdown of interaction networks involving bees and beetles but not that of flies and wasps.
Journal Article
Only multi-taxon studies show the full range of arthropod responses to fire
Fire is a major driver in many ecosystems. Yet, little is known about how different ground-living arthropods survive fire. Using three sampling methods, and time-since-fire (last fire event: 3 months, 1 year, and 7 years), we investigate how ground-living arthropod diversity responds to fire, and how species richness, diversity, abundance, and composition of the four dominant taxa: ants, beetles, cockroaches and mites, respond. We did this in the naturally fire-prone Mediterranean-type scrubland vegetation (fynbos) of the Cape Floristic Region. Surprisingly, overall species richness and diversity was the same for all time-since-fire categories. However, when each dominant taxon was analysed separately, effect of fire on species richness and abundance varied among taxa. This emphasizes that many taxa must be investigated to really understand fire-driven events. We also highlight the importance of using different diversity measures, as fire did not influence species richness and abundance of particular taxa, while it affected others, overall greatly affecting assemblages of all taxa. Rockiness affected species richness, abundance and composition of a few taxa. We found that all time-since-fire categories supported distinctive assemblages. Some indicator species occurred across all time-since-fire categories, while others were restricted to a single time-since-fire category, showing that there is a wide range of responses to fire between taxa. Details of local landscape structure, abiotic and biotic, and frequency and intensity of fire add complexity to the fire-arthropod interaction. Overall, we show that the relationship between fire and arthropods is phylogenetically constrained, having been honed by many millennia of fire events, and highly complex. Present-day species manifest a variety of adaptations for surviving the great natural selective force of fire.
Journal Article
Identifying managerial legacies within conservation corridors using remote sensing and grasshoppers as bioindicators
Biodiversity conservation under global change requires effective management of key biodiversity areas, even areas not under formal protection. Natural grassland conservation corridors between plantation forests are such areas, as they improve landscape connectivity, mitigate the impact of landscape fragmentation, and conserve biodiversity. However, empirical evidence is required to identify the extent to which past management actions promote effectiveness of conservation corridors into the future. We address this issue using grasshoppers, which are well-established indicators of habitat quality. In particular, we assess grasshopper response within corridors to historic grassland photosynthetic activity using a 25-yr normalized difference vegetation index (NDVI) time series. We then use vegetation characteristics measured in the field to understand the potential mechanisms driving grasshopper response. Furthermore, we explore the efficacy of satellite remote sensing for monitoring grasshopper habitat using additive models. We found that grasshopper evenness responded positively to deviation in NDVI within a 3-yr period, whereas assemblage composition responded positively over a shorter time of two years. Grasshopper richness and evenness responded strongly to the local vegetation height and bare ground, whereas grasshopper assemblage composition also responded to plant species richness. We found a major negative impact of the invasive alien bramble (Rubus cuneifolius) on large-sized grasshoppers and species of conservation concern. Overall, the results illustrate the importance of maintaining primary high-quality habitat for maintaining grasshopper diversity, alongside removal of invasive bramble. We recommend prescribed burning to maintain high-quality habitat heterogeneity, with sites burned within three years. Furthermore, high-resolution satellite imagery is effective for monitoring grasshopper richness and assemblage composition response to changes in vegetation within the corridors. Grassland conservation corridors do conserve biodiversity, although effective management and monitoring needs to be in place to ensure biodiversity resembles that of neighbouring protected areas.
Journal Article
New policy directions for global pond conservation
Despite the existence of well‐established international environmental and nature conservation policies (e.g., the Ramsar Convention and Convention on Biological Diversity) ponds are largely missing from national and international legislation and policy frameworks. Ponds are among the most biodiverse and ecologically important freshwater habitats, and their value lies not only in individual ponds, but more importantly, in networks of ponds (pondscapes). Ponds make an important contribution to society through the ecosystem services they provide, with effective conservation of pondscapes essential to ensuring that these services are maintained. Implementation of current pond conservation through individual site designations does not function at the landscape scale, where ponds contribute most to biodiversity. Conservation and management of pondscapes should complement current national and international nature conservation and water policy/legislation, as pondscapes can provide species protection in landscapes where large‐scale traditional conservation areas cannot be established (e.g., urban or agricultural landscapes). We propose practical steps for the effective incorporation or enhancement of ponds within five policy areas: through open water sustainable urban drainage systems in urban planning, increased incentives in agrienvironment schemes, curriculum inclusion in education, emphasis on ecological scale in mitigation measures following anthropogenic developments, and the inclusion of pondscapes in conservation policy.
Journal Article
Effects of both climate change and human water demand on a highly threatened damselfly
While climate change severely affects some aquatic ecosystems, it may also interact with anthropogenic factors and exacerbate their impact. In dry climates, dams can cause hydrological drought during dry periods following a great reduction in dam water discharge. However, impact of these severe hydrological droughts on lotic fauna is poorly documented, despite climate change expected to increase drought duration and intensity. We document here how dam water discharge was affected by climate variability during 2011–2018 in a highly modified watershed in northeastern Algeria, and how an endemic endangered lotic damselfly,
Calopteryx exul
Selys, 1853 (Odonata: Calopterygidae), responded to hydrological drought episodes. Analysis was based on a compilation of data on climate (temperature, precipitation, and drought index), water dam management (water depth and discharge volume and frequency), survey data on
C. exul
occurrence, and capture–mark–recapture (CMR) of adults. The study period was characterized by a severe drought between 2014 and 2017, which led to a lowering of dam water depth and reduction of discharge into the river, with associated changes in water chemistry, particularly during 2017 and 2018. These events could have led to the extirpation of several populations of
C. exul
in the Seybouse River (Algeria). CMR surveys showed that the species was sensitive to water depth fluctuations, avoiding low and high water levels (drought and flooding). The study shows that climate change interacts with human water requirements and affects river flow regimes, water chemistry and aquatic fauna. As drought events are likely to increase in the future, the current study highlights the need for urgent new management plans for lotic habitats to maintain this species and possible others.
Journal Article
Asynchrony among insect pollinator groups and flowering plants with elevation
Mountains influence species distribution through differing climate variables associated with increasing elevation. These factors determine species niche ranges and phenology. Although the distribution patterns of some specific insect groups relative to elevation have been determined, how differing environmental conditions across elevation zones differentially influence the phenology of various insect groups is largely unknown. This is important in this era of rapid climate change. We assess here how species composition and seasonal peaks in abundance among different insect pollinator groups and flowering plants differ across four floristically distinct elevation zones up a sentinel mountain subject to strong weather events. We sampled insect pollinators in four major groups (bees, wasps, beetles and flies) over two spring seasons. Pollinator species composition across all elevation zones tracks flowering plant species composition. In terms of abundance, beetles were the dominant group across the three lower zones, but declined greatly in the summit zone, where flies and bees were more abundant. Bee abundance peaked earlier than the other groups across all four elevation zones, where there were significant peaks in abundance. Bee abundance peaked earlier than flowering plants at the middle zone and slightly later than flowering plants at the base zone, suggesting a mismatch. We conclude that, while elevation shapes species distribution, it also differentially influences species phenology. This may be of great significance in long-term assessment of species distribution in sensitive mountain ecosystems.
Journal Article
Wild Herbivore Grazing Enhances Insect Diversity over Livestock Grazing in an African Grassland System
Southern Africa's grassland biodiversity is threatened by habitat transformation such as commercial forestry. Ecological networks (ENs) have been instigated to alleviate the pressure of habitat transformation on local biodiversity. ENs are large scale webs of corridors and patches of natural vegetation criss-crossing production landscapes that can simulate conditions in protected areas (PAs). Many ENs have lost many native large mammal species, which have been replaced by domestic livestock to retain natural grazing dynamics, which could have an impact on the long-term value of ENs for insects. Here we compared dung beetle, butterfly and grasshopper diversity in ENs across a landscape mosaic of timber plantations, where 1) wild megaherbivores were maintained, 2) in ENs where these herbivores were replaced by livestock and, 3) in a nearby World Heritage PA which retained its natural complement of megaherbivores. Sites in the PA far from any plantation were similar in composition to those in the wild grazed EN. Presence of the wild grazers improved the alpha- and beta-diversity of all focal insect taxa when compared to domestic grazing. Furthermore, species composition shows significant differences between the two grazing systems indicating that an assemblage of native large mammals facilitates insect diversity conservation. We support the maintenance or introduction of large native mammals in ENs or similar conservation areas in production landscapes to simulate the ecological conditions and natural heterogeneity in nearby PAs.
Journal Article
Eco‐evolutionary origins and diversification in a megadiverse hotspot: Arthropods in the Greater Cape Floristic Region
The Greater Cape Floristic Region at the southern tip of Africa is a global megadiversity hotspot. The region's biodiversity has been driven by a long history of topographic, climatic, and sea level change coupled with geological uplift, and without being exposed to any major climate events such as glaciations since the breakup of Gondwana. Among arthropods, this long history has led to the survival of many ancient lineages, manifested by much disparity followed by considerable speciation in more recent times, with the emergence of many cryptic species flocks. There is much convergence among the various taxa and functional groups in how they have responded to the various environmental filters of the past. There has also been the development of a great many morphological, behavioral, and microhabitat specialisms, associated with both topography and particular habitats, as well as interactions with other organisms. Morphological and molecular advances are elucidating how this megadiversity came about. There are indications that among the arthropod fauna, especially species that are small‐sized and have cryptic lifestyles, many more taxa remain to be discovered. Here, we review the eco‐evolutionary trends that have occurred in this region and that have resulted in such remarkable arthropod diversity. Conservation of the arthropod fauna requires recognition of this historical biogeography and ecology. Instigation of approaches over wide areas is required so as to encompass all this diversity. The Greater Cape Floristic Region at the southern tip of Africa is a global megadiversity hotspot. The region's biodiversity has been driven by a long history of topographic, climatic, and sea level change coupled with geological uplift, and without being exposed to any major climate events such as glaciations since the breakup of Gondwana. Here, we review the eco‐evolutionary trends that have occurred in this region and that have resulted in the remarkable arthropod diversity.
Journal Article
Condition-dependent survival and movement behavior in an endangered endemic damselfly
Movement is essential for the maintenance of populations in their natural habitats, particularly for threatened species living in fluctuating environments. Empirical evidence suggests that the probability and distance of movement in territorial species are context-dependent, often depending on population density and sex. Here, we investigate the movement behavior of the spring cohort of an endangered endemic damselfly
Calopteryx exul
in a lotic habitat of Northeast Algeria using capture-mark-recapture (CMR) of adults. By sampling 10 gridded river stretches across a 2 km section of the watercourse, we were able to estimate the distance of movement throughout individual lifespans and estimate movement probability for both males and females. We used multistate models to examine whether individual density and sex ratio influence survival and movement probability. We found that males and females had similar movement kernels with most individuals moving short distances (83% performing movements of < 100 m and only 1% > 1000 m). Of the 547 marked individuals, 63% were residents, and 37% were movers (moved at least 50 m from one sampling occasion to another). Survival probability showed higher estimates for females and was slightly density-dependent (i.e., lower survival probabilities were associated with high male densities). Survival probability did not show a marked difference between residents and movers. Movement probability and distances were positively correlated with individual density, but were not or slightly correlated with sex ratio, respectively. These results are not in line with the hypotheses of sex-biased movement and survival costs of movement. Our results suggest that the species performs mostly short-distance movements that are dependent on intraspecific interactions.
Journal Article