Gradient Of Land-use Intensity Research Articles

Land use patterns skew sex ratios, decrease genetic diversity and trump the effects of recent climate change in an endangered turtle

AbstractAimChanges in both land use and climate can cause population declines and species extinctions, but the relative effects of these two stressors are often dependent on species‐specific life histories. Turtles are highly threatened as a taxonomic group and are particularly sensitive to environmental change due to their life history, habitat preferences and physiology. We used both sex data and genetic diversity across a landscape‐scale gradient in land use intensity and recent climate change to characterize the relative effects of these factors on three turtle species (including the endangered Blanding's turtle, Emydoidea blandingii) with different life histories and thus different vulnerabilities to environmental change.LocationWisconsin, USA.MethodsTurtles were captured and sampled for genetic analyses at 18 sites. Sampled individuals were genotyped for species‐specific sets of microsatellite markers, and population‐level genetic diversity was assessed using rarefied allelic richness and heterozygosity. The relative effects of road density, public land area and recent climate change on genetic diversity and sex ratio were evaluated using regression methods and model‐selection criteria.ResultsIncreased land use intensity was associated with male‐skewed sex ratios and decreased genetic diversity in E. blandingii but not co‐occurring species. Recent climate change did not explain variability in either sex ratio or genetic diversity for any of the three species examined.Main conclusionsChanging land use has multiple impacts on turtle populations that are modulated by species‐specific life history traits. Extensive terrestrial movements associated with nesting in E. blandingii increase female vulnerability to road mortality, which in turn has led to declines in genetic diversity. The predicted effects of recent climate change may have been dampened by behavioural plasticity. We suggest that the disproportionate effect of land use on E. blandingii warrants greater legal protection for this species.

Shifts from native to invasive small mammals across gradients from tropical forest to urban habitat in Borneo

Urbanization has paved the way for the spread of commensal rodents at global scale. However, it is largely unknown how these species use tropical anthropogenic landscapes originally covered with forests and inhabited by diverse small mammal assemblages. We surveyed non-flying small mammals in various urban and suburban habitat types and adjacent forest in the tropical town of Kota Kinabalu in Borneo. We used occupancy and polynomial regression models to determine variation in species occurrences along gradients of land-use intensity. Muller’s sundamys (Sundamys muelleri) was the only native small mammal species found in urban and suburban landscapes with a continuous decrease in occurrence probability from forests to urban habitats. The invasive Asian black rat (Rattus rattus species complex) and the invasive Asian house shrew (Suncus murinus) had the highest occurrence probabilities in habitats of intermediate land-use intensity, but Asian black rats are also likely to occasionally invade forested habitats and occupied urban habitats in sympatry with the Norway rat (Rattus norvegicus). In urban and suburban habitats, fallow land possibly favoured the occurrence of S. muelleri and S. murinus. Other native small mammal species (Muridae, Sciuridae, Tupaiidae) were found only in forested areas. Our study shows that native small mammals found in forest are largely replaced by invasive species in urban and suburban habitats. Due to their occurrence in habitats of various land use intensities, S. muelleri and R. rattus comprise central links between forest wildlife and urban species, an association that is important to consider in studies of parasite and disease transmission dynamics.

Labile soil organic carbon and nitrogen within a gradient of dryland agricultural land-use intensity in Wyoming, USA

Tillage in dryland winter wheat (Triticum aestivum L.)–summer fallow cropping systems of the central High Plains, USA, has caused significant erosion and loss of soil organic matter (SOM), underscoring the need for more sustainable practices on marginally-productive semiarid lands. Conversion to no-till (NT) wheat–fallow or perennial grass–legume cover, as in the Conservation Reserve Program (CRP), provides viable alternatives to tillage-based wheat–fallow practices. However, the overall impact of transitioning on soil biogeochemistry is not fully understood. Labile SOM pools were determined on soil cores (0–120cm) collected in July 2011 from five unfertilized fields that spanned a gradient in disturbance associated with land-use practices: a more intensively tilled wheat–fallow (‘historic’, HT) than a conventional (CT) wheat–fallow with limited herbicides combined with tillage, NT wheat–fallow that exclusively used herbicides for ≥10years, formerly cultivated HT wheat–fallow planted to grass–legume mixture as in the CRP for 7years, and native prairie (NP) with no history of agricultural disturbance. Significant differences in microbial biomass C (MBC), potentially mineralizable C (PMC) and nitrogen (PMN) were largely confined to the surface soil (0–30cm), following the order NP>CRP>all wheat–fallow systems. When expressed on a per soil organic C (SOC) basis, both MBC and PMC followed the order CRP>NP>all wheat–fallow systems. In contrast, when normalized by total soil N (TN), PMN was higher in HT and CT soils than in other soils (NT, CRP, and NP). MBC and PMC were positively correlated with SOC whereas PMN, soil pH, and electrical conductivity (EC) showed a negative relationship with SOC. These results suggest more efficient conservation of SOM under perennial grass–legume system than NT wheat–fallow rotation. We suggest that cessation of tillage alone may not be sufficient for the recovery of labile-pool SOM degraded through long-term cultivation in the absence of inputs for soil fertility renewal.

Avian biodiversity in multiple-use landscapes of the Brazilian Amazon

Habitat loss and degradation is the most pervasive threat to tropical biodiversity worldwide. Amazonia sits at the frontline of efforts to both improve the productivity of tropical agriculture and prevent the loss of biodiversity. To date our understanding of the biodiversity impacts of agricultural expansion in Amazonia is restricted to findings from small scale studies that typically assess the importance of a limited number of land-use types. Here we investigate local and landscape-scale responses of Amazonian avian assemblages to land-cover changes across a gradient of land-use intensity ranging from undisturbed primary forest to mechanised agriculture in 36 drainage catchments distributed across two large regions of the eastern Brazilian Amazon. We found that species richness of forest-associated birds declined progressively along this gradient, accompanied by marked shifts in assemblage composition. We found significant changes in species composition, but not richness, between primary forests that had been subject to different levels of disturbance from logging and fire. Secondary forests retained levels of species richness intermediate between primary forests and production areas, but lacked many forest-dependent species. Production areas (arable crops, cattle pastures and plantation forests) all retained far fewer species than any forest habitat, and were largely dominated by taxa commonly associated with open areas. Diversity partitioning revealed that species composition varied the most among undisturbed forest transects, and steadily decreased with increasing forest degradation and land-use intensity. Our results emphasise the importance of protecting both remaining areas of primary forest in private lands, as well as protecting the same forests from further disturbance events.

Traits of butterfly communities change from specialist to generalist characteristics with increasing land-use intensity

Land-use intensification leads to species loss and shifts in community composition, but only few studies examine how these dynamics affect ecological and life-history traits. We thus investigated whether ecological and life-history traits differ between butterfly communities of grasslands with different land-use intensity. We conducted butterfly transect surveys in 137 grassland sites in three regions of Germany and compiled 10 species-specific ecological and life-history traits from the literature. These traits are associated with food plant specialisation, dispersal, distribution, reproduction and development. We calculated a land-use intensity gradient based on the amount of fertilise mowing frequency and grazing intensity. We analysed differences of traits characteristics between butterfly communities along the land-use intensity gradient in a fourth-corner analysis, thus considering correlations between traits. Six ecological and life-history traits changed from characteristics associated with specialists to such associated with generalists with increasing land-use intensity. These traits characteristics in intensified grasslands were: high dispersal propensity, large distribution range, low population density, more than one generation per year, hibernation in a more advanced developmental stage and a long flight period. The functional homogenisation of the butterfly communities with changes from specialist to generalist trait characteristics with increasing land-use intensity may have severe consequences for ecosystem functioning and services.

Can REDD+ Help the Conservation of Restricted-Range Island Species? Insights from the Endemism Hotspot of São Tomé

REDD+ aims to offset greenhouse gas emissions through “Reduced Emissions from Deforestation and forest Degradation”. Some authors suggest that REDD+ can bring additional benefits for biodiversity, namely for the conservation of extinction-prone restricted-range species. Here, we assess this claim, using São Tomé Island (Democratic Republic of São Tomé and Príncipe) as a case study. We quantified the abundance of bird and tree species, and calculated the aboveground carbon stocks across a gradient of land-use intensity. We found a strong spatial congruence between carbon and the presence and abundance of endemic species, supporting the potential of REDD+ to protect these taxa. We then assessed if REDD+ could help protect the forests of São Tomé and Príncipe. To do so, we used OSIRIS simulations to predict country-level deforestation under two different REDD+ designs. These simulations showed that REDD+ could promote the loss of forests in São Tomé and Príncipe through leakage. This happened even when additional payments for biodiversity were included in the simulations, and despite São Tomé and Príncipe having the fourth highest carbon stocks per land area and the second highest biodiversity values according to the OSIRIS database. These results show weaknesses of OSIRIS as a planning tool, and demonstrate that the benefits that REDD+ might bring for biodiversity are strongly dependent on its careful implementation. We recommend that payment for ecosystem services programmes such as REDD+ develop safeguards to ensure that biodiversity co-benefits are met and perverse outcomes are avoided across all tropical countries. In particular, we advise specific safeguards regarding the conservation of extinction-prone groups, such as island restricted-range species.

Ecological traits affect the response of tropical forest bird species to land-use intensity

Land-use change is one of the main drivers of current and likely future biodiversity loss. Therefore, understanding how species are affected by it is crucial to guide conservation decisions. Species respond differently to land-use change, possibly related to their traits. Using pan-tropical data on bird occurrence and abundance across a human land-use intensity gradient, we tested the effects of seven traits on observed responses. A likelihood-based approach allowed us to quantify uncertainty in modelled responses, essential for applying the model to project future change. Compared with undisturbed habitats, the average probability of occurrence of bird species was 7.8 per cent and 31.4 per cent lower, and abundance declined by 3.7 per cent and 19.2 per cent in habitats with low and high human land-use intensity, respectively. Five of the seven traits tested affected the observed responses significantly: long-lived, large, non-migratory, primarily frugivorous or insectivorous forest specialists were both less likely to occur and less abundant in more intensively used habitats than short-lived, small, migratory, non-frugivorous/insectivorous habitat generalists. The finding that species responses to land use depend on their traits is important for understanding ecosystem functioning, because species' traits determine their contribution to ecosystem processes. Furthermore, the loss of species with particular traits might have implications for the delivery of ecosystem services.

Natural and cultural heritage in mountain landscapes: towards an integrated valuation

Mountain areas of Europe have been managed by humans for a long time, leading to a prevalence of semi-natural habitats in mountain landscapes today. These landscapes contain both natural and cultural heritage; however, natural and cultural heritage are rarely considered together when valuing landscapes and developing management plans in protected areas. Here we present a case study of seven protected areas in the mountains of Great Britain and Norway. We take a long-term perspective on landscape and land-use change and propose an integrated model of landscape valuation on the basis of combined natural and cultural heritage. Our model plots indicators of natural and cultural heritage along a gradient of land-use intensity, allowing simultaneous assessment and highlighting how valuation depends on what type of heritage is considered. We show that while contemporary land-use changes follow similar trajectories in Norway and Britain, different land-use histories mean that the loss of heritage differs between the regions. The model presented here thus allows for the consolidation of valuation based on both cultural and natural heritage in landscapes.

Community mean traits as additional indicators to monitor effects of land-use intensity on grassland plant diversity

Semi-natural grasslands, biodiversity hotspots in Central-Europe, suffer from the cessation of traditional land-use. Amount and intensity of these changes challenge current monitoring frameworks typically based on classic indicators such as selected target species or diversity indices. Indicators based on plant functional traits provide an interesting extension since they reflect ecological strategies at individual and ecological processes at community levels. They typically show convergent responses to gradients of land-use intensity over scales and regions, are more directly related to environmental drivers than diversity components themselves and enable detecting directional changes in whole community dynamics. However, probably due to their labor- and cost intensive assessment in the field, they have been rarely applied as indicators so far. Here we suggest overcoming these limitations by calculating indicators with plant traits derived from online accessible databases. Aiming to provide a minimal trait set to monitor effects of land-use intensification on plant diversity we investigated relationships between 12 community mean traits, 2 diversity indices and 6 predictors of land-use intensity within grassland communities of 3 different regions in Germany (part of the German ‘Biodiversity Exploratory’ research network). By standardization of traits and diversity measures, use of null models and linear mixed models we confirmed (i) strong links between functional community composition and plant diversity, (ii) that traits are closely related to land-use intensity, and (iii) that functional indicators are equally, or even more sensitive to land-use intensity than traditional diversity indices. The deduced trait set consisted of 5 traits, i.e., specific leaf area (SLA), leaf dry matter content (LDMC), seed release height, leaf distribution, and onset of flowering. These database derived traits enable the early detection of changes in community structure indicative for future diversity loss. As an addition to current monitoring measures they allow to better link environmental drivers to processes controlling community dynamics.

DIEL CHANGES OF DISSOLVED ORGANIC MATTER IN STREAMS OF VARYING WATERSHED LAND USE

ABSTRACTWe examined diel changes in dissolved organic matter (DOM) under summer low‐flow conditions for six streams selected across a gradient of agricultural land use intensity (21%–73% cropland). Trends in concentration [dissolved organic carbon (DOC) concentration] and optical properties of DOM showed a high degree of synchrony. During a 24‐h period, DOC changed by between 2.9 and 4.3 mg L−1. For all sites, the highest DOC was observed during dark periods and the lowest concentration during light periods. DOM sampled during daylight hours was more complex (humic) as determined using specific absorbance. DOM source, measured using fluorescence spectroscopy, usually varied during the 24‐h period, but few similarities in temporal fluorescence trends were identified between sites. Human landscape alterations appear to have little direct influence on the temporal nature of diel DOM dynamics in our study region. However, our results indicate that landscape characteristics are likely more broadly important in defining the magnitude temporal change in DOC. Woodland areas were negatively correlated with early afternoon DOC (r2 = 0.89, p = 0.005), positively correlated with diel percent change in DOC (r2 = 0.87, p = 0.007) and positively with diel change in discharge (r2 = 0.64, p = 0.054). Together, these results indicate the likely influence of differing riparian transpiration rates and changing subsurface inputs on DOC loading. Reduced DOC and discharge rates during daylight hours resulted in a mean underestimation of DOC export rate by 61% for early afternoon versus early morning sampling. Variation in the dominant source of DOM entering theses streams was strongly related to agricultural land use, and DOM in high cropland streams was more microbially derived. In addition, high cropland streams also exhibited the lowest minimum dissolved oxygen concentrations, a pattern related to high rates of productivity at these sites. Copyright © 2012 John Wiley & Sons, Ltd.

Host tree utilization by epiphytic orchids in different land-use intensities in Kathmandu Valley, Nepal

We studied the influence of site conditions on epiphytic orchids under a subtropical climate in the Kathmandu Valley, Nepal. We analysed 96 systematically distributed grid points situated in Kathmandu Valley across a land-use intensity gradient (national park to urbanised city area). Geographical Information System (GIS) and remote sensing were used for classification of land-use types. We identified 23 species of epiphytic orchids, within 13 genera, from 42 different host tree species. Host preference is obvious for some orchid species (e.g., Dendrobium nobile), with certain tree species (e.g., Schima wallichii, Ficus religiosa) hosting more orchid species than others. The orchid Rhynchostylis retusa was the most common species found on many different host tree species across the land-use intensity gradient. Host species and host bark characteristics (e.g., rugosity, pH and exposure to wind) played a vital role for orchid distribution, with lower abundance in areas of higher impact. Under strong human impact (urban city area), F. religiosa was the dominant host tree, with large individual trees (mean diameter in breast height, dbh = 1.3 m) providing the habitat for considerable populations of R. retusa individuals. In general, epiphytic orchids were found on larger host trees in urban areas than in areas of lower human impact. We found that some hosts are more likely to harbour orchid species, especially native host species. Older larger trees with rougher bark, low pH, exposed to wind and reduced human impact provided better habitats for orchids. We suggest these characteristics should be considered in urban planning to reduce human impact on the associated orchid epiphytic community.

Are Dung Beetles Driving Dung-Fly Abundance in Traditional Agricultural Areas in the Amazon?

We evaluated the effects of different land-use systems on the ability of dung beetles to control the population of detritus-feeding flies. We tested the hypotheses that intensification of land use will reduce dung beetles richness, abundance and biomass and, consequently, their dung burial ability, affecting the interaction between dung beetles and flies and reducing its effectiveness as a natural biological control. In the Brazilian Amazon we sampled dung beetles, fly larvae and adults; and recorded the rate of dung removal by dung beetles across a gradient of land-use intensity from primary forest, secondary forest, agroforestry, agriculture to pasture. Our results provide evidence that land-use intensification results in a reduction of the richness, abundance and biomass of dung beetles, and this in turn results in lower rates of dung removal in the most simplified systems. We found no significant differences in the abundance of fly larvae between the different systems of land use. However, the number of adult flies differed significantly between land-use systems, presenting higher abundance in those sites with greater intensity of use (pasture and agriculture) and a lower abundance of adult flies in forested systems (primary and secondary forests, and agroforestry). Information-theoretic model selection based on AICc revealed strong support for the influence of land-use systems, dung removal rates and dung beetle abundance, biomass and richness on adult dung-fly abundance. Our results also reveal that dung beetles are not solely responsible for fly control and that other factors linked to land use are influencing the populations of these detritus-feeding insects.

A large-scale forest fragmentation experiment: the Stability of Altered Forest Ecosystems Project

Opportunities to conduct large-scale field experiments are rare, but provide a unique opportunity to reveal the complex processes that operate within natural ecosystems. Here, we review the design of existing, large-scale forest fragmentation experiments. Based on this review, we develop a design for the Stability of Altered Forest Ecosystems (SAFE) Project, a new forest fragmentation experiment to be located in the lowland tropical forests of Borneo (Sabah, Malaysia). The SAFE Project represents an advance on existing experiments in that it: (i) allows discrimination of the effects of landscape-level forest cover from patch-level processes; (ii) is designed to facilitate the unification of a wide range of data types on ecological patterns and processes that operate over a wide range of spatial scales; (iii) has greater replication than existing experiments; (iv) incorporates an experimental manipulation of riparian corridors; and (v) embeds the experimentally fragmented landscape within a wider gradient of land-use intensity than do existing projects. The SAFE Project represents an opportunity for ecologists across disciplines to participate in a large initiative designed to generate a broad understanding of the ecological impacts of tropical forest modification.

Plant leaf economics and reproductive investment are responsive to gradients of land use intensity

Relationships between functional leaf traits across large sets of plant species emphasized the existence of a major axis describing a trade-off between rapid acquisition and conservation of resources forming the so-called “leaf economics spectrum”. It is uncertain which environmental factors determine the economics spectrum and whether traits associated with reproduction co-vary with the economics spectrum. To determine these trait–environment relationships for agricultural ecosystems, this study was conducted at field, pasture, and heathland sites forming a strong land use gradient in Northwest Germany. The abundance of 49 species was recorded in 85 plots together with their traits (canopy height, specific leaf area, leaf N, leaf N:P, leaf and stem dry matter content, life cycle, reproductive investment (RI) in seed mass and seed number), as well as parameters describing soil resources and land use disturbances. RLQ multivariate analysis of the data set related an environmental table to a species trait table using a species abundance table to extract the joint structure between them. Thereafter, we clustered the species on the RLQ axis to extract functional groups. Traits associated with the leaf economics spectrum were strongly related to soil resources that co-varied with disturbance intensity. A division of the whole land use gradient into agricultural and heathland sites showed that RI was not decoupled from trait–environment relationships although the direction of the RI–environment relationship was opposite in the two subsets. Species were clumped rather than linearly arranged in the trait–environment space and the functional groups broadly corresponded to weed communities, pastures with differing intensities, and heathlands. The trade-off in plant economics responding to soil resources supports predictions of previous theoretical and empirical work. Different RI–environment relationships in agricultural sites and heathlands emphasize the relevance of local scales in trait–environment studies. In general, the results point to some of the biological mechanisms controlling functions and services of agricultural ecosystems.

Rapid assessment of headwater stream macroinvertebrate diversity: an evaluation of surrogates across a land-use gradient

Implementation of policies about the conservation and restoration of aquatic ecosystems' biodiversity and ecological integrity requires rapid assessment methods. The landscapes of the Carpathian Mountains, spanning an unusually steep gradient of land-use intensity from a European perspective, offer great opportunities for evaluating such methods. Focusing on the orders Ephemeroptera, Plecoptera and Trichoptera (EPT), we evaluated three approaches for assessing macroinvertebrate species richness in second and third order streams: (1) the use of data at higher taxonomic levels, (2) the use of species-level data, and (3) the use of abundance data. The number of families was a reliable indicator of species richness within EPT. Species richness of Trichoptera was strongly correlated to species richness in Ephemeroptera and Plecoptera, and thus in the EPT group as a whole, whereas species richness in Ephemeroptera and Plecoptera did not perform as well. We found little evidence for the usefulness of abundance data as a surrogate for species richness within orders, except in Plecoptera. Taxa richness in EPT was generally positively related to forest cover in the catchments and negatively related to the proportion of agricultural land. EPT taxa richness could be used to distinguish between High/Good quality classes and those of lower ecological quality according to the EU Water Framework Directive. Our results suggest that assessments focusing on the family level provide a cost-efficient alternative to species-level assessments in second and third order streams, and point at Trichoptera as a potential indicator group.

Early succession arthropod community changes on experimental passion fruit plant patches along a land-use gradient in Ecuador

Many tropical landscapes are today characterized by small forest patches embedded in an agricultural mosaic matrix. In such highly fragmented landscapes, agroforests have already been recognized as refuges for biodiversity but few studies have investigated the potential of non-forested land-use types to contribute to overall biodiversity of functionally important taxa in the tropics. This study experimentally investigated species richness, abundance, and community similarity of arthropods on Yellow Passion fruit plants, planted in standardized patches in 30 sites along a land-use intensity gradient. The gradient comprised all major land-use types of the area: forest fragments, abandoned coffee agroforests, coffee agroforests managed under shade trees, pastures, and rice fields in Coastal Ecuador. We found a total of 2123 individuals belonging to 242 species. Overall arthropod species richness increased with light intensity and leaf-surface area and decreased with land-use intensity: forest fragments and abandoned coffee agroforests harboured significantly more species than rice or pastures. Overall diversity in managed coffee agroforests was intermediate between the intensively managed and more natural habitats. However, the three most abundant taxa of arthropods (ants, spiders, and beetles) had the highest number of species in managed coffee agroforests, while ant abundance was highest in abandoned coffee agroforests and spider abundance highest in managed coffee agroforests. Analyses of community similarity revealed that open (pasture, and rice) and shaded (forest, abandoned and managed coffee agroforests) land-use types had distinct arthropod communities. In conclusion, although open agricultural land-use types tend to have fewer species in lower numbers, all land-use types contribute to overall biodiversity of the agricultural matrix because of distinct communities in shaded vs. non-shaded land-use types.

Changes in nematode abundances and body length in response to management intensive grazing in a low-input temperate pasture

An evaluation of changes in nematode populations in response to management was performed using a field scale experiment along a gradient of land-use intensity in the context of management intensive grazing. Four levels of decreasing intensity were measured over three growing seasons. The treatments included: 1) intensive grazing management where cows were allowed to graze for each grazing cycle, followed by routine clipping and harrowing; 2) semi-intensive grazing where cows were allowed to graze for each grazing cycle, with only one clipping event per year; 3) extensive grazing where cows were allowed to graze during every 2nd grazing cycle and no clipping or harrowing was performed; 4) stockpiling treatment where cows were permitted to graze only during the final grazing cycle, followed by clipping at the end of the season. Most indices (MI, PPI, ∑MI, and ∑MI25) resulted in significant seasonal differences; however, only familial diversity (H′) and the total number of families showed significant season by treatment interaction. Bacterivores comprised most of the nematode population with Cephalobidae being the most common family. Abundance of plant feeders was affected by season and soil moisture, whereas bacterivore abundance was associated with total organic N and soil pH. Nematode body length increased slightly in most families through time, and was associated with season, bulk density, soil moisture, and total N and C. Although omnivore numbers were highest in the extensive and semi-intensive treatments, there was a significant increase in dorylaimid body length observed in the intensive treatment through time. Increases in body length were also observed in Monhysteridae and Cephalobidae in all treatments.

Tree visitation and seed dispersal of wild cherries by terrestrial mammals along a human land-use gradient

The role of terrestrial mammals as seed dispersers of fleshy-fruited plants has only rarely been investigated in temperate regions although recent studies underline the importance of these animals for long-distance seed dispersal. Here we examine the potential role of mammals as seed dispersers of wild cherry ( Prunus avium L.) along a gradient of human land-use intensity. We placed camera traps at 21 wild cherry trees to identify the mammal species that visited the trees. We conducted feeding trials to test if the recorded species were legitimate seed dispersers or seed predators and to assess gut passage times. We tested the influence of human land-use intensity by quantifying habitat and landscape structure around the study trees at different spatial scales and analyzing its influence on visitation rates of tree visitors. Red fox ( Vulpes vulpes ), roe deer ( Capreolus capreolus ), wild boar ( Sus scrofa ), marten ( Martes spp.) and badger ( Meles meles ) were identified as seed dispersers of wild cherry, of which wild boar was largely a seed predator. Habitat and landscape structure at local spatial scales (70 m, 500 m radius) had no effect on the total visitation rates of mammals. At larger spatial scales (1.0–10.0 km radius) total visitation rates increased with increasing proportion of extensively used farmland and seminatural habitat in the area. The proportion of forest had no influence on visitation rates. The results suggest that high proportions of extensively used farmland and seminatural habitat increase the visitation and seed dispersal rates of large mammals. Comparing gut passage times with home range sizes and daily travel distances suggests that these mammals have the potential to disperse seeds over long distances and can provide gene flow in fragmented agricultural landscapes. Die Rolle von bodenlebenden Säugetieren als Ausbreiter von Samen fleischiger Früchte wurde in den gemäßigten Breiten nur wenig untersucht, obwohl neuere Studien die Bedeutung dieser Tiere für die Ausbreitung über lange Distanzen unterstreichen. Wir untersuchen die Rolle bodenlebender Säuger als Samenausbreiter der Wildkirsche ( Prunus avium L.) entlang eines Landnutzungsgradienten. Wir stellten Kamerafallen an 21 Untersuchungsbäumen auf, um die baumbesuchenden Säuger zu identifizieren. Wir führten Fütterungsversuche durch, um herauszufinden, ob die beobachteten Arten Samenausbreiter oder Samenprädatoren waren und um die Magen-Darmpassagezeiten abzuschätzen. Um den Einfluss anthropogener Landnutzung auf die Besuchsaktivität der baumbesuchenden Säuger zu testen, wurden Habitat- und Landschaftsstruktur auf verschiedenen räumlichen Maßstäben um die Untersuchungsbäume quantifiziert. Rotfuchs ( Vulpes vulpes ), Reh ( Capreolus capreolus ), Wildschwein ( Sus scrofa ), Marder ( Martes spp.) und Dachs ( Meles meles ) wurden als Samenausbreiter der Wildkirsche identifiziert, wobei Wildschweine meist Samenprädatoren waren. Die Habitat- und Landschaftsstruktur auf lokalem Maßstab (70 m, 500 m Radius) hatte keinen Effekt auf die Gesamt-Besuchsaktivität der Säugetiere an den Kirschbäumen. Auf größerem räumlichen Maßstab (1,0–10,0 km Radius) stieg die Besuchsaktivität mit ansteigendem Anteil an extensiver Landwirtschaft und semi-natürlicher Habitate. Der Anteil an Wald hatte keinen Einfluss auf die Besuchsaktivität der Säuger an Wildkirschbäumen. Diese Ergebnisse lassen vermuten, dass hohe Anteile extensiv landwirtschaftlich genutzter Flächen und semi-natürlichem Habitat die Besuchsaktivität großer Säugetiere erhöhen und damit auch die Samenausbreitung steigern. Der Vergleich von Magen-Darmpassagezeiten, Streifgebietsgrößen und täglich zurückgelegten Strecken legt nahe, dass diese Säuger das Potential haben, Samen über lange Distanzen auszubreiten, und damit den Genfluss in fragmentierten, landwirtschaftlich geprägten Gebieten aufrecht erhalten können.

Responses of common buzzard ( Buteo buteo) and Eurasian kestrel ( Falco tinnunculus) to land use changes in agricultural landscapes of Western France

In front of land use changes, there has been a wide decline in biodiversity. In this study, we analysed the numerical response of two diurnal raptor species, the common buzzard and the Eurasian kestrel to different agricultural landscape contexts. We carried out a 3-year survey of the abundance of these two species in three agricultural landscape contexts that are known to form a gradient of land use intensity and hedgerow network fragmentation. We also considered the variation in prey abundance related to these land use changes. The two raptor species showed negative but differentiated response patterns to land use intensification and small mammal abundance. The abundance of the common buzzard decreased significantly with the reduction of hedgerows, woodlots and grasslands areas, as well as with the decrease in prey abundance at the landscape scale. The abundance of the Eurasian kestrel showed the same trend, but fall of abundance was less marked and not significant. This resulted in a reverse ratio of species density according to agricultural intensification and landscape openness. Specific feeding habits, nesting habitats and spatial partitioning in foraging areas could explain the difference in the numerical response observed for these two raptor species. Buzzards forage mainly on highly profitable prey areas and avoid highly fragmented woodland habitats for nesting. Kestrels seem less dependent on semi-natural habitats, are able to nest in more fragmented landscapes and are better adapted to exploit less abundant but more widespread small mammal prey species within the cultivated matrix. The study may help to evaluate carrying capacities of agricultural landscapes in accordance with ecological life traits of these two raptor species.

Metal and metallothionein content in bullfrogs: Study of a whole watershed impacted by agricultural activities

Among the various anthropogenic activities potentially affecting amphibian populations, agriculture has often been evoked. Fertilizers used in agriculture are documented sources of metals that may contaminate nearby rivers. Bullfrogs ( Rana catesbeiana) were collected within the Yamaska River basin (Quebec, Canada) along a gradient of agricultural land use intensity. Hepatic, renal and intestinal metal content, along with hepatic metallothionein content, were determined. In general, dissolved metal concentrations and accumulated metal concentrations in bullfrogs varied little among sites. Hepatic Cu and Zn concentrations were significantly different among subwatersheds and were in accordance with the gradient in agricultural activities in at least one of the three years studied. Liver metallothionein content did not vary significantly among the subwatersheds, but they were correlated with Cu content within two sites and Cd content at one site. We conclude that R. catesbeiana could be used as a biomonitor for Cu contamination and potentially for other metals.