Positive Edge Effects Research Articles

Urban wild bees benefit from flower-rich anthropogenic land use depending on bee trait and scale

ContextWild bees are important pollinators for wild and cultivated plants. Besides other causes, their decline has been linked to land-use change such as urbanisation. In contrast, urban habitats are discussed as potential wild bee refuges.ObjectivesTo expand our understanding of cities as wild bee habitats, bee responses to urban land-use types with varying foraging and nesting resources were analysed.MethodsWild bees were sampled with pan traps at 49 study sites in a Central European city. Effects of land-use types on wild bees were examined at 12 scales ranging from 50 to 1500 m from sampling points. For analyses, bees were grouped according to their traits (e.g., size, nesting and pollen-collecting behaviour) to account for species-specific requirements.ResultsLand-use types significantly affected wild bees covering all investigated scales. Anthropogenically managed flower-rich habitats, i.e., long-term allotments and cemeteries, were beneficial for most wild bee groups within varying scales between 200 and 600 m. Impervious surface affected only some of the investigated wild bee groups, mostly in a unimodal manner within a 100 m scale.ConclusionsThis study shows that it is recommended for future investigations to take different scales and different bee traits into account when assessing urban habitat quality for bees. In particular, the non-linear response to impervious surface indicates positive edge effects between urban core and rural areas. Conservation measures and implementation management to support wild bees in urban areas should consider the results on scale and land use to meet species-specific demands effectively.

Edge grassland provide a stronger thermal buffer against core grassland in the agro-pastoral ecotone of Inner Mongolia

The impact of land use/cover change on land surface temperature is an important topic in research on biodiversity, environment planning, sustainability. However, such studies are rare in grassland ecosystems. Based on morphological spatial pattern analysis, we analyzed the change in grassland landscape patterns in the agro-pastoral ecotone of Inner Mongolia from 2000 to 2020. We also examined the impact of grassland landscape pattern change on productivity and land surface temperature. We found that the grassland area decreased significantly, with grassland fragmentation increasing during the past 20 years. A series of landscape types showed different area changes: the area of islet and perforation increased, and the area of core, edge, and bridge decreased. Compared with the core grassland, the edge grassland shows higher productivity, which is a positive edge effect. Moreover, the edge grassland has a lower daytime temperature, higher nighttime temperature, and a smaller daily range than that in the core grassland. Our study highlights that the edge grassland has higher productivity and stronger thermal buffering. We suggest that more attention should be paid to the edge areas in grassland management to alleviate the thermal stress caused by human induced climate change.

Seasonal effects of edge and habitat complexity on eelgrass epifaunal assemblages

Habitat degradation and fragmentation reduce habitat structural complexity (e.g. amount of physical features) and increase habitat edges. While many studies have focused on the effects of habitat edges or complexity on biodiversity, relatively few have disentangled them or investigated their effects over time. We investigated how proximity to the edge of eelgrassZosterasubg.Zostera marinaLinnaeus, 1753 habitat, shoot density and their interactions across seasons can influence the diversity pattern of epifaunal assemblages in meadows situated in a Mediterranean lagoon (France). We used a combination of field sampling andin situmanipulations with artificial seagrass units (ASUs) mimicking low and high shoot densities. During autumn and spring, we found that shoot density, Z. marina biomass and leaf area index (LAI) were higher inside the meadows than at the edge, while epiphyte load was the highest in spring at the edges. Epifaunal abundance and diversity were higher at the edge than inside the meadow for both natural shoots—regardless of the epiphyte load—and ASUs in spring. In autumn, epifaunal abundance varied positively with ASU density, regardless of the position in the meadow. Our results also showed that edges and habitat complexity affect the epifaunal structure differently across seasons. Therefore, we suggest that recruitment of macrofauna is the main mechanism explaining a positive edge effect during spring. This work highlights the need to consider seasonal dynamics in the assessment of habitat fragmentation and degradation.

Comparing alternative methods of modelling cumulative effects of oil and gas footprint on boreal bird abundance

ContextOil and gas activity is increasing in the western boreal forest of North America. To manage cumulative effects of this industry, a better quantification of footprint effects on wildlife is needed.ObjectivesWe used point-count surveys to evaluate how well footprint amounts within 150 m, and proximity to seismic lines, pipelines, well sites, roads, and energy facilities predicted the abundance of 48 bird species.MethodsWe developed models for each species, evaluating the best functional forms for different footprint effects, then predicted how different model structures influenced estimates of regional population size.ResultsMost species exhibited at least one nonlinear response to footprint amount (79% of species) or distance (88%). Species associated with older coniferous forests decreased more often with increased footprint amount and closer proximity to footprint, while species associated with open lands and young forests increased with greater footprint and closer proximity. In one-third of species, bird abundance versus distance changed from a positive to negative relationship (or reverse) at a threshold distance from at least one footprint. Models based on footprint proximity had better fit than those based on footprint amount for 29 of 48 species, but both model types produced similar population estimates.ConclusionsBoth footprint amount and proximity models were useful for assessing cumulative effects on wildlife and mechanisms causing change. Models of distance to footprint can provide evidence of positive or negative edge effects for developing management buffers. Models of footprint amount provide important information on functional changes in habitat.

Positive Edge Effects of Natural Habitats Produce Matching Response in Beetle Population and Plant Morphometry in Amaranth Crop

Components of a surrounding agricultural matrix can be important to the ecology of agroecosystems because they modulate biodiversity, abundance of pests (i.e., arthropods or weeds), and their natural enemies. Based on the assumption that organisms respond to edges, we assessed whether animals (beetles) and crop plants showed similar patterns across a gradient of perturbation and ecotones and natural habitats. Across the perturbation gradient, we analyzed (1) crop plant morphometry and (2) the structure of beetle populations in the perturbed area and natural habitats. Results showed that beetles (a bioindicator group) and A. hypochondriacus crop plants (perturbed area) responded similar to an ecotone, i.e., we found positive edge effects, but beetle richness negatively followed the gradient of perturbation affecting beetle nestedness and turnover. At the point nearest the ecotone, crop plants grew larger (e.g., panicle and plant height had the largest effects), which was consistent in time. Results supported the resource competition framework and resource distribution model in agroecosystems.

High ecosystem service delivery potential of small woodlands in agricultural landscapes

Abstract Global forest loss and fragmentation have strongly increased the frequency of forest patches smaller than a few hectares. Little is known about the biodiversity and ecosystem service supply potential of such small woodlands in comparison to larger forests. As it is widely recognized that high biodiversity levels increase ecosystem functionality and the delivery of multiple ecosystem services, small, isolated woodlands are expected to have a lower potential for ecosystem service delivery than large forests hosting more species. We collected data on the diversity of six taxonomic groups covering invertebrates, plants and fungi, and on the supply potential of five ecosystem services and one disservice within 224 woodlands distributed across temperate Europe. We related their ability to simultaneously provide multiple ecosystem services (multiservice delivery potential) at different performance levels to biodiversity of all studied taxonomic groups (multidiversity), forest patch size and age, as well as habitat availability and connectivity within the landscape, while accounting for macroclimate, soil properties and forest structure. Unexpectedly, despite their lower multidiversity, smaller woodlands had the potential to deliver multiple services at higher performance levels per area than larger woodlands of similar age, probably due to positive edge effects on the supply potential of several ecosystem services. Biodiversity only affected multiservice delivery potential at a low performance level as well as some individual ecosystem services. The importance of other drivers of ecosystem service supply potential by small woodlands in agricultural landscapes also depended on the level of performance and varied with the individual ecosystem service considered. Synthesis and applications. Large, ancient woodlands host high levels of biodiversity and can therefore deliver a number of ecosystem services. In contrast, smaller woodlands in agricultural landscapes, especially ancient woodlands, have a higher potential to deliver multiple ecosystem services on a per area basis. Despite their important contribution to agricultural landscape multifunctionality, small woodlands are not currently considered by public policies. There is thus an urgent need for targeted policy instruments to ensure their adequate management and future conservation in order to either achieve multiservice delivery at high levels or to maximize the delivery of specific ecosystem services.

Tree performance in a biodiversity enrichment experiment in an oil palm landscape

AbstractLarge‐scale conversion of tropical forests into oil palm monocultures has led to dramatic losses of biodiversity and ecosystem functions. While ecological restoration is urgently needed in many oil palm landscapes, there is a lack of scientific knowledge of sustainable management strategies.We established experimental tree islands of varying sizes (25 m2to 1,600 m2) and diversity levels (1, 2, 3 and 6 species) in an oil palm plantation in Sumatra, Indonesia. Six native multi‐purpose tree species includingArchidendron pauciflorum(Jengkol),Durio zibethinus(Durian),Parkia speciosa(Petai),Shorea leprosula(Meranti),Peronema canescens(Sungkai) andDyera polyphylla(Jelutung) were planted between living and felled oil palms. Here, we analyse the controlling factors of tree growth and survival during the first 4 years at the level of local neighbourhood and tree island.We found a significant effect of diversity levels on tree productivity, that is, basal area was higher in multi‐species than in single‐species tree islands. This overyielding was attributed to enhanced tree growth, while mortality had no effect. In the local neighbourhood, tree species richness had a positive effect on tree growth during the first year only, indicating that selection and dominance of well‐performing species at high level of diversity are most likely driving overyielding.Trees grew better away from living oil palms, suggesting tree‐palm competition. Proximity to felled oil palms increased growth especially during the first years, during which the planted trees might have benefited from the additional available space and resources. Despite positive edge effects from the conventional oil palm management in the surrounding, tree island size had an overall positive effect on tree growth.Synthesis and applications. We planted native trees in an oil palm landscape following a tree island pattern. The establishment success differed widely among the six planted species. The selection of particular species is a decisive factor to foster a positive relationship between diversity and tree growth. Planting larger tree islands (e.g. 1,600 square metres) is a better option to enhance tree growth, but tree‐palm competition implies a trade‐off between tree growth and palm oil production in the tree islands.

O uso de sistemas agroflorestais diversificados na restauração florestal na Mata Atlântica

Com a nova legislação ambiental brasileira vislumbra-se a possibilidade do uso de sistemas agroflorestais diversificados para recompor áreas de preservação permanente e reserva legal, principalmente em pequenas propriedades rurais. Uma pergunta que surge, diz respeito a capacidade desses sistemas em reduzir custos na restauração florestal e ao mesmo tempo apresentar eficiência ecológica similar aos plantios em que se faz uso exclusivo de espécies nativas do bioma em questão. Buscando a resposta avaliou-se nesse estudo um sistema agroflorestal implantado em 2005, em Seropédica, RJ, que tinha o objetivo de interligar dois fragmentos florestais ali existentes. Desde então foram feitas uma série de avaliações sobre a eficácia ecológica desse “corredor agroflorestal” na interligação desses fragmentos. Os resultados indicaram que a quantidade e a qualidade da fauna do solo e fungos micorrízicos foram favorecidos pelo sistema agroflorestal em comparação à matriz de pastagem, mas ainda se encontram em níveis inferiores aos fragmentos florestais interligados. A pastagem próxima ao sistema agroflorestal vem se beneficiando da melhoria ambiental ali existente, criando um “efeito de borda positivo”, situação bem distinta da pastagem que se encontrava mais distante da área de influência do corredor agroflorestal. Para os indicadores utilizados, o sistema agroflorestal foi eficiente.

Positive roadside edge effects on artificial nest survival in a lowland Atlantic Forest.

Road construction is considered to be one of the primary causes of forest fragmentation, and little is known about how roads affect bird reproductive success. The objective of this study was to assess the survival rate of artificial nests along an edge associated with a highway and in the interior of a tabuleiro forest. The study was performed at the Sooretama Biological Reserve, on the margins of federal highway BR‐101, between September and October 2015. A total of 168 artificial nests with a Common quail (Coturnix coturnix) egg in each nest were placed along six sampling transects, at distances of 2, 25, 50, 100, 200, 400, and 800 m from the highway toward the forest interior. We used logistic regression and estimated daily survival rate (DSR) using the “Nest Survival” function in the program MARK to estimate artificial nest survival and assessed the effect of the distance from the highway. The artificial nest survival rate was significantly higher on the highway margins than at other distances. The results show that artificial nests located up to 25 m from the highway have a greater success probability (over 95%) and a significant decrease in success probability more than 50 m from the highway. Although we cannot rule out other nonroad‐specific edge effects on artificial nest predation, our results suggest that the impacts of the highway (e.g., noise, vibration, visual stimuli) cause predators to avoid the road's surroundings (up to 25 m into the forest) when selecting their feeding sites, which partially supports the predation release hypothesis.

The influence of anthropogenic edge effects on primate populations and their habitat in a fragmented rainforest in Costa Rica.

When a forest is fragmented, this increases the amount of forest edge relative to the interior. Edge effects can lead to loss of animal and plant species and decreased plant biomass near forest edges. We examined the influence of an anthropogenic forest edge comprising cattle pasture, coconut plantations, and human settlement on the mantled howler (Alouatta palliata), white-faced capuchin (Cebus capucinus), Central American spider monkey (Ateles geoffroyi), and plant populations at La Suerte Biological Research Station (LSBRS), Costa Rica. We predicted that there would be lower monkey encounter rate, mean tree species richness, and diameter at breast height (DBH) in forest edge versus interior, and that monkeys would show species-specific responses to edge based on diet, body size, and canopy height preferences. Specifically, we predicted that howler monkeys would show positive or neutral edge effects due to their flexible folivorous diet, large body size, and preference for high canopy, capuchins would show positive edge effects due to their diverse diet, small body size, and preference for low to middle canopy, and spider monkeys would show negative edge effects due their reliance on ripe fruit, large body size, and preference for high upper canopy. We conducted population and vegetation surveys along edge and interior transects at LSBRS. Contrary to predictions, total monkey encounter rate did not vary between the forest edge and forest interior. Furthermore, all three species showed neutral edge effects with no significant differences in encounter rate between forest edge and interior. Interior transects had significantly higher mean tree species richness than edge transects, and interior trees had greater DBH than edge trees, although this difference was not significant. These results suggest that forest edges negatively impact plant populations at La Suerte but that the monkeys are able to withstand these differences in vegetation.

Ecological Responses to Habitat Fragmentation Per Se

For this article, I reviewed empirical studies finding significant ecological responses to habitat fragmentation per se—in other words, significant responses to fragmentation independent of the effects of habitat amount (hereafter referred to as habitat fragmentation). I asked these two questions: Are most significant responses to habitat fragmentation negative or positive? And do particular attributes of species or landscapes lead to a predominance of negative or positive significant responses? I found 118 studies reporting 381 significant responses to habitat fragmentation independent of habitat amount. Of these responses, 76% were positive. Most significant fragmentation effects were positive, irrespective of how the authors controlled for habitat amount, the measure of fragmentation, the taxonomic group, the type of response variable, or the degree of specialization or conservation status of the species or species group. No support was found for predictions that most significant responses to fragmentation should be negative in the tropics, for species with larger movement ranges, or when habitat amount is low; most significant fragmentation effects were positive in all of these cases. Thus, although 24% of significant responses to habitat fragmentation were negative, I found no conditions in which most responses were negative. Authors suggest a wide range of possible explanations for significant positive responses to habitat fragmentation: increased functional connectivity, habitat diversity, positive edge effects, stability of predator–prey/host–parasitoid systems, reduced competition, spreading of risk, and landscape complementation. A consistent preponderance of positive significant responses to fragmentation implies that there is no justification for assigning lower conservation value to a small patch than to an equivalent area within a large patch—instead, it implies just the opposite. This finding also suggests that land sharing will usually provide higher ecological value than land sparing.

Natural vegetation cover in the landscape and edge effects: differential responses of insect orders in a fragmented forest.

Human activities have led to global simplification of ecosystems, among which Neotropical dry forests are some of the most threatened. Habitat loss as well as edge effects may affect insect communities. Here, we analyzed insects sampled with pan traps in 9 landscapes (at 5 scales, in 100-500 m diameter circles) comprising cultivated fields and Chaco Serrano forests, at overall community and taxonomic order level. In total 7043 specimens and 456 species of hexapods were captured, with abundance and richness being directly related to forest cover at 500 m and higher at edges in comparison with forest interior. Community composition also varied with forest cover and edge/interior location. Different responses were detected among the 8 dominant orders. Collembola, Hemiptera, and Orthoptera richness and/or abundance were positively related to forest cover at the larger scale, while Thysanoptera abundance increased with forest cover only at the edge. Hymenoptera abundance and richness were negatively related to forest cover at 100 m. Coleoptera, Diptera, and Hymenoptera were more diverse and abundant at the forest edge. The generally negative influence of forest loss on insect communities could have functional consequences for both natural and cultivated systems, and highlights the relevance of forest conservation. Higher diversity at the edges could result from the simultaneous presence of forest and matrix species, although "resource mapping" might be involved for orders that were richer and more abundant at edges. Adjacent crops could benefit from forest proximity since natural enemies and pollinators are well represented in the orders showing positive edge effects.

Edge effects in the avifaunal community of riparian rain-forest tracts in Tropical North Queensland

AbstractMost evidence suggests anthropogenic edges negatively affect rain-forest bird communities but little has been done to test this in Australasia. In this study, avifaunal detection frequency, species richness and community composition were compared between the edge and interior and between flat and more complex-shaped edges of riparian rain-forest tracts in Tropical North Queensland. The detection frequency and richness of guilds based on diet, foraging strata and habitat specialism were also compared. This study detected 15.1% more birds at the rain-forest edge compared with the interior but no difference in species richness. Edge shape had no effect on detection frequency or richness. Many guilds (subcanopy, closed forest, frugivorous and insectivorous species) experienced increased detection frequency at the edge relative to the interior, but for some guilds this response was reduced (habitat generalists) or reversed (understorey and mixed-flock species) along complex edges. Overall community composition was affected by edge distance but not by edge shape. Edge habitat was shorter and had more open canopy than the interior, supporting habitat-based explanations for the observed avifaunal edge effects. These results suggest generally positive edge effects in Australian rain-forest bird communities, possibly reflecting local resource distributions or a disturbance-tolerant species pool.

Predicting forest management effects on oak–rodent mutualisms

Wood mice Apodemus sylvaticus are the main dispersers of acorns in highly managed Mediterranean holm‐oak woodlands. Mice mobilize and cache acorns to store them for winter consumption. They carry acorns away from potential competitors, face predation risks during mobilization, and cache acorns in areas where pilfering risks are low. However, mice can act either as net predators or as moderately efficient dispersers, depending on the way landscape management affects intraspecific competition for acorns and shelter availability. To assess the influence of landscape structure and mouse behavior on acorn dispersal, we developed an agent‐based model (ABM) that translates forest management into changes in key environmental factors driving mouse foraging decisions.The model was able to predict accurately acorn dispersal patterns in a wide range of forest management practices based on information on forest habitat availability, stem density and shrub cover. Sensitivity analysis revealed that caching rates emerged from the interplay between intraspecific competition for seeds and predation risk accepted during mobilization. It also showed that intraspecific competition for acorns decreased with increasing habitat loss (due to positive edge effects on acorn production) while landscape resistance to mouse movements increased. As a result, the net benefits of caching declined and acorn predation became the dominant strategy. Finally, we assessed the effects of shrub encroachment as a management practice to enhance dispersal services in savanna‐like landscapes (dehesas). The model predicted non‐linear responses with a 65% threshold of shrub cover needed to achieve relatively high levels of acorn dispersal. This value may not be compatible with the traditional exploitation of dehesas (livestock rearing). Our study shows that integrated approaches that combine environmental change driven by management with behavioral responses of dispersers improve our understanding of the causes of recruitment bottlenecks, and are useful tools for evaluating conservation strategies aimed at enhancing dispersal services.

The “edge effect” phenomenon: deriving population abundance patterns from individual animal movement decisions

Edge effects have been observed in a vast spectrum of animal populations. They occur where two conjoining habitats interact to create ecological phenomena that are not present in either habitat separately. On the individual-level, an edge effect is a change in behavioral tendency on or near the edge. On the population-level, it is a pattern of population abundance near an edge that cannot be explained in terms of either habitat in isolation. That these two levels of description exist suggests there ought to be a mathematical link between them. Here, we make inroads into providing such a link, deriving analytic expressions describing oft-observed population abundance patterns from a model of movement decisions near edges. Depending on the model parameters, we can see positive, negative, or transitional edge effects emerge. Importantly, the distance over which animals make their decisions to move between habitats turns out to be a key factor in quantifying the magnitude of certain observed edge effects.

Do leaf‐cutting ants benefit from forest fragmentation? Insights from community and species‐specific responses in a fragmented dry forest

Abstract The expansion of agriculture has led to forest loss and fragmentation, resulting in dramatic biodiversity impoverishment. Surprisingly, few studies have assessed forest fragmentation effects on leaf‐cutting ant assemblages, and none has dealt with effects on their community richness and composition, despite their known role as key herbivores and ecosystem engineers. We analysed forest area and edge effects on leaf‐cutting ant abundance, richness and assemblage composition, by recording and identifying colonies along edge and interior transects in 12 Chaco Serrano forest remnants of different sizes, in Central Argentina. We also explored leaf‐cutting ant presence in the adjacent soybean matrix. We recorded five leaf‐cutting ant species, in the genus Acromyrmex. In the soybean matrix, colonies of three species were observed, which were also found at the forest edge. Within the forest, edges sustained more species and colonies than interior habitats, whereas forest area was linked positively to colony abundance. Taxonomic composition of leaf‐cutting ant assemblages reflected both area and edge effects. Our results revealed overall positive edge and area effects on leaf‐cutting ant communities, highlighting differential species‐specific responses and a possible role for Acromyrmex crassispinus as a forest status indicator. According to our findings, an increase in edge habitats may favour most leaf‐cutting ant species, providing a suitable interface for access to the cultivated matrix, but hindering species associated with undisturbed forest conditions. As leaf‐cutting ants are acknowledged as cornerstones of ecosystem functioning, the consequences of these trends may be far reaching.

Plant beta‐diversity is enhanced around grassland–forest edges within a traditional agricultural landscape

AbstractQuestionsAre there positive edge effects on beta‐ and alpha‐diversity of plant species across semi‐natural grassland–secondary forest gradients located within a traditional agricultural landscape? Is beta‐diversity (dissimilarity in plant species composition between two given plots) well explained by environmental differences for both grasslands and forests? Do gradients of environmental factors created by forest edges influence spatial variation in alpha‐diversity from edges to grasslands and forests?LocationSemi‐natural grasslands and secondary forests (or conifer plantation) around paddy fields in a traditional agricultural landscape, western Japan.MethodsVegetation survey and environmental (soil water content and sunlight) measurements were conducted on 11 transects passing through grassland–forest ecosystems. Spatial variations in plant beta‐ and alpha‐diversity and environmental variables and their relationships were examined.ResultsWe quantitatively demonstrated common positive edge effects on beta‐diversity in both grasslands and forests. Our results suggest that among‐edge variations in light conditions, which likely depend on edge aspect and forest type, promote high grassland plant beta‐diversity in the vicinity of edges. However, the high beta‐diversity of forest floor communities in the proximity of edges cannot be explained by this mechanism. Alpha‐diversity tended to be lower within grassland plots located around edges than in grassland interiors, while the richness of the forest community increased toward the edge. This alpha‐diversity pattern was suggested to be attributable to resource gradients created by the forest edges.ConclusionsAlthough plant alpha‐diversity may not be consistently high in the vicinity of edges, beta‐diversity in the communities bordering grassland–forest edges will generally be high in the traditional agricultural landscape. Thus, maintenance of environmental heterogeneity among grassland–forest edges in agricultural ecosystems should be prioritized for local biodiversity conservation.

Edge effects are important in supporting beetle biodiversity in a gravel-bed river floodplain.

Understanding complex, dynamic, and diverse ecosystems is essential for developing sound management and conservation strategies. Gravel-bed river floodplains are composed of an interlinked mosaic of aquatic and terrestrial habitats hosting a diverse, specialized, and endangered fauna. Therefore, they serve as excellent models to investigate the biodiversity of multiple ecotones and related edge effects. In this study, we investigated the abundance, composition, richness, and conservation status of beetle assemblages at varying sediment depth (0, 0.1, 0.6 and 1.1 m), distance from the channel (1, 5, 20, and 60–100 m, and 5 m within the riparian forest), and time of the year (February–November) across a 200 m-wide gravel bar at the near-natural Tagliamento River (Italy), to detect edge effects in four floodplain ecotones: aquatic-terrestrial, forest-active floodplain, sediment-air, and sediment-groundwater. We used conventional pitfall traps and novel tube traps to sample beetles comparably on the sediment surface and within the unsaturated sediments. We found a total of 308 beetle species (including 87 of conservation concern) that showed multiple, significant positive edge effects across the floodplain ecotones, mainly driven by spatial heterogeneity: Total and red list beetle abundance and richness peaked on the sediment surface, at channel margins, and at the edge of the riparian forest. All ecotones possessed edge/habitat specialists. Most red list species occurred on the sediment surface, including five species previously considered extinct – yet two of these species occurred in higher densities in the unsaturated sediments. Conservation and management efforts along gravel-bed rivers must therefore promote a dynamic flow and sediment regime to create and maintain habitat heterogeneity and ecotone diversity, which support a unique and high biodiversity.

Bat distribution size or shape as determinant of viral richness in african bats.

The rising incidence of emerging infectious diseases (EID) is mostly linked to biodiversity loss, changes in habitat use and increasing habitat fragmentation. Bats are linked to a growing number of EID but few studies have explored the factors of viral richness in bats. These may have implications for role of bats as potential reservoirs. We investigated the determinants of viral richness in 15 species of African bats (8 Pteropodidae and 7 microchiroptera) in Central and West Africa for which we provide new information on virus infection and bat phylogeny. We performed the first comparative analysis testing the correlation of the fragmented geographical distribution (defined as the perimeter to area ratio) with viral richness in bats. Because of their potential effect, sampling effort, host body weight, ecological and behavioural traits such as roosting behaviour, migration and geographical range, were included into the analysis as variables. The results showed that the geographical distribution size, shape and host body weight have significant effects on viral richness in bats. Viral richness was higher in large-bodied bats which had larger and more fragmented distribution areas. Accumulation of viruses may be related to the historical expansion and contraction of bat species distribution range, with potentially strong effects of distribution edges on virus transmission. Two potential explanations may explain these results. A positive distribution edge effect on the abundance or distribution of some bat species could have facilitated host switches. Alternatively, parasitism could play a direct role in shaping the distribution range of hosts through host local extinction by virulent parasites. This study highlights the importance of considering the fragmentation of bat species geographical distribution in order to understand their role in the circulation of viruses in Africa.

Forest remnants contribute to parasitoid conservation: experimental evaluation of parasitism on a leafminer host

Worldwide, intense forest fragmentation has resulted in mosaic landscapes in which biodiversity and a number of important ecological processes are threatened. Insect parasitism is a vital component of herbivore population regulation, hence the study of parasitism and parasitoid richness in fragmented forests embedded in an agricultural matrix is relevant from conservation and management perspectives. Here, we investigated through experimental field exposure of the leafminer Liriomyza commelinae (Diptera: Agromyzidae) the effects of forest remnant size and edge/interior location on parasitism, species richness and parasitoid community composition. Two consecutive experiments were performed in which pots with mined plants were placed in remnants of Chaco Serrano forests in Central Argentina. Parasitism levels (on average above 50 %) and number of parasitoids species (in total, 20 species) were independent of forest remnant size. However, higher parasitism and species richness were found at the forest edge compared with the interior although the differences in species richness failed to reach statistical significance. Parasitoid community composition was not related to forest size whereas assemblages from interior habitats showed closer similarity than those from the edges. The results suggest forest remnants could play an important role as reservoirs of parasitoids with potential to control crop pests, a possibility heightened by the positive edge effects which could facilitate the transfer of this valuable ecosystem service to the adjacent cultivated land.