Seed Rain and Seed Limitation in a Planted Gallery Forest in Brazil

With seeds collected monthly during one year from 53 1‐m² seed traps, we investigated the seed rain and seed limitation in a gallery forest planted in 1994 in SE Brazil. Contrasting animal‐ (zoochorous) and wind‐dispersed (anemochorous) plants we investigated (1) which aspects of the composition and structure of the vegetation influence the abundance and species richness of the seed rain; (2) if such influences differ between zoochorous and anemochorous seeds; (3) if the abundance and richness of the seed rain sampled under zoochorous and nonzoochorous plant species differ; and (4) if seed limitation (given by the proportion of sites to which seeds were not dispersed) differs between zoochorous and anemochorous plant species, and also between species that have been planted and those that further colonized the area (colonists). Seed rain was intense and dominated by anemochorous species. The overall seed rain was not influenced by the vegetation parameters we analyzed (canopy height and cover, plant size, abundance, and richness) or by the plant species above the seed trap. The abundance and richness of zoochorous seeds in a given spot was influenced by the abundance and richness of zoochorous plants in its immediate vicinity. Seed limitation was higher for anemochorous than zoochorous species and higher for planted than for colonist species. We concluded with recommendations for the initial establishment of a planted forest, including the homogeneous distribution of zoochorous plants to permit a spatially homogeneous zoochorous seedfall, which will likely enhance the chances of survival and successful establishment of seeds.     

Dung beetle (Coleoptera: Scarabaeinae) persistence in Amazonian forest fragments and adjacent pastures: biogeographic implications for alpha and beta diversity

The aim of this study is to analyze the effects of habitat loss and forest replacement by cattle pasture on the alpha and beta diversity, abundance, biomass and species composition of dung beetles with different dispersal ability. Dung beetles were captured in 19 forest fragments and neighbouring pastures. Forest fragment area ranged from 3.7 to 4825 ha and in this study were grouped into four categories: small, medium, large and control forest. A total of 35,048 dung beetles representing 101 species were collected. Forest fragments had the highest richness with 81 species, followed by pasture with 58 species. Replacement of forest by pasture reduced species richness; however, due to the proximity and connectivity of these areas with Cerrado patches, pastures also had high species richness, but species composition was independent of adjacent fragments. Small fragments had lower abundance and species richness than our other habitat categories, even pastures. Our results highlight that proximity and connectivity with Cerrado areas influenced the patterns of alpha and beta diversity of dung beetles in fragments and pastures. We highlight that the ability to cross the pasture matrix is a strong adaptive trait for species living in human-modified landscapes. Consequently, species with these abilities are less susceptible to the effects of forest fragmentation and local extinction. Our results reinforce the importance of considering the biogeographic location and distribution pattern of species in forest fragmentation studies.     

Seed Dispersal Modes of the Sandstone Plateau Vegetation of the Middle Caquetá River Region,Colombian Amazonia1

We characterized the dispersal spectra and phenology of 298 vascular plant species of the sandstone plateaus of Colombian Amazonia. Dispersal modes were determined by the morphology of dispersion units, personal observations on fruit consumption, and an extensive literature review. We obtained the number of species per dispersal mode for the sandstone plateaus and for two recognized vegetation types: open‐herbaceous vegetation and low forest‐shrub vegetation. Dispersal modes were assigned to 295 plant species. Animals dispersed the highest percentage of species (46.6%), while the percentage of autochorous and anemochorous species was 29.4 and 23 percent, respectively. The dispersal spectrum of the low forest‐shrub vegetation type, based on the coverage of every species, showed that percentages of anemochorous (40.2%) and zoochorous species (37.8%) were similar. Autochory was the most important seed dispersal mode of the open‐herbaceous vegetation (60%). Birds were the principal group of potential dispersers (58.9%) of zoochorous species and reptiles the least important. We found two marked fruiting peaks, one from the end of the dry season to the beginning of the wet season and the second one from the beginning to the middle of the dry season. Our results showed that besides the differences in the vegetation structure and floristic composition between the sandstone plateaus and the adjacent tall forest, there also exist differences in the dispersal spectra and the fruiting rhythms.     

Landscape connectivity dynamics based on network analysis in the Xishuangbanna Nature Reserve,China

Lack of landscape connectivity and habitat loss is major threats to biodiversity and ecosystem integrity in nature reserves aimed at conservation. In this study, we used structural pattern and functional connectivity metrics to analyze the spatial patterns and landscape connectivity of habitat patches for the Shangyong sub-reserve of the Xishuangbanna Nature Reserve from 1970, 1990, and 2000. On the basis of vegetation and land cover data, we applied the equivalent connected area ECA(PC) indicator to analyze the changes in forest connectivity. Four distance thresholds (2, 4, 8, 12 km) were considered to compare the patch importance of connectivity by dECA values. The results showed the declining trends of landscape connectivity measured by ECA(PC) index from 1970 to 2000. The importance of connectivity in each forest patch varied with the increment of dispersal distances at the patch level, and some important habitat patches, which exhibit a potential to enhance landscape connectivity, should be given more attention. The least-cost pathways based on network structure were displayed under four dispersal distances in three periods. The results showed that the number of paths among the fragments of forest patches exhibited radical increases for larger dispersal distances. Further correlation analyses of AWF, ECA (IIC), and ECA (PC) showed the weakest and least-frequent correlations with the structural pattern indices, while H presented more significant correlations with the PD fragmentation metric. Furthermore, Kendall's rank correlations between the forest patch area and functional connectivity indicators showed that dECA (PC) and dAWF indicators should provided the area-based prioritization of habitat patches. Moreover, the low-rank correlations showed that dF and dLCP can be considered as effective and appropriate indicators for the evaluation of habitat features and network patterns.     

Dispersal mode constrains allocation of carbon and mineral nutrients in seeds of forest and savanna trees

• Species vary in seed size and content of stored reserves, which can be related to dispersal strategies and type of habitat in which they are found. We compare seed carbon and nutrient reserves of anemochorous and zoochorous trees from the Cerrado of central Brazil.
• We measured seed dry mass, lipids, non‐structural carbohydrates (starch and total soluble sugars), carbon and mineral nutrients in ten forest and 13 savanna species, each classified as having wind‐ or animal‐dispersed seeds. We used phylogenetically independent contrasts to test for correlations among these traits.
• Seeds of anemochorous species were lighter, with higher concentrations of C, N, P, Ca and Mg. Lipids were the dominant carbon reserve for most anemochorous species, underpinning the importance of allocation to compact carbon reserves. Starch, lipids or soluble sugars were the major carbon reserve in zoochorous seeds. Savanna and forest species did not differ in seed mass or in total carbon reserves. However, seeds of forest species had higher concentrations of starch than seeds of savanna species. Lipid and starch negatively correlated across species, suggesting a trade‐off between starch and lipids as major seed carbon reserves. Calcium was positively correlated with Mn and B, while Mg was positively correlated with C, N, P, K, S, Zn and B. Potassium, S and Cl were positively correlated, while P was positively correlated with Mg and Zn.
• Dispersal mode rather than vegetation type constrained seed mass and seed storage allocation patterns in forest and savanna trees. We provide evidence that similar mechanisms are involved in seed storage of carbon and mineral nutrients across species.

     

Dispersal of forest birds and trees along the Uruguay River in southern South America

The Uruguay River starts in Serra do Mar in Brazil runs through the Paranense forest and flows southward through grassland and savannas. It has a continuous gallery forest of 750 km from the southern border of the Paranense forest to the river mouth. The gallery forest extends for 100 km more along the Río de la Plata. 125 (68.7%) of the 182 species of forest birds recorded in the southern Paranense forest penetrate into the gallery forest of the Uruguay River and only 13 (7.1%) reach the end of the gallery forest (Punta Lara). The number of bird species is inversely correlated (r² = 0.942) with distance and the slope of the regression is 58.10. This means a decline in diversity with 32% of species lost per unit distance. A hundred and eighty forest tree species were recorded in the southern Paranense forest, of which 113 (62.8%) penetrate into the gallery forest of the Uruguay River, and 28 (15.6%) reach Punta Lara. The number of tree species is inversely correlated (r² = 0.976) with distance and the slope of the regression is ?45.62. This means a decline in diversity with 25% of species lost per unit distance. The Uruguay River enables the dispersal of many species of forest birds and trees from the rain forest, but species richness tends to decrease with increased distance from the source area. A clear association pattern was found for birds between size, diet, habitat use and distance reached into the gallery forest. Species of smaller body size, granivores, insectivores and those that use both the interior and exterior parts of the gallery forest advanced noticeably further along the river than larger species, carnivores, nectarivores or frugivores, and those that frequent only a part of the forest. Similarly, a clear association between dispersal mechanism, water dependence and distance reached into the gallery forest was found for trees. Species with vegetative reproduction, zoochorous species and riparian species advanced markedly longer distances along the river than, anemochorous species and non‐riparian species.     

Colonization Credit in Restored Wet Heathlands

Although human‐driven landscape modification is generally characterized by habitat destruction and fragmentation, it may also result in the creation of new habitat patches, providing conditions conducive to spontaneous colonization. In this article, we propose the concept of “colonization credit” (i.e., the number of species yet to colonize a patch, following landscape changes) as a framework to evaluate the success of colonization, in terms of species richness, in new/restored habitats, taking into account the spatial structure of landscapes. The method mirrors similar approaches used to estimate extinction debt in the context of habitat fragmentation, that is, comparisons, between old and new habitat patches, of the relationships among spatial patch metrics and patch species richness. We applied our method to the case of spontaneous colonization of newly created habitat patches suitable for wet heathland plant communities in South Belgium. Colonization credit was estimated for the total species richness, the specialist species richness, and the species richness of three emergent groups (EGs) of specialist species, delineated on the basis of dispersal traits. No significant colonization credit was identified either in patches created 25–55 years ago or in those created within the past 25 years, with the exception of species from our first EG (mostly anemochorous species with long‐term persistent seed bank). However, the differential response of species in that first EG could not be explained through their characteristic life history traits. The results of this study are encouraging and suggest that deliberate, directed restoration activities could yield positive developments in a relatively short period of time.     

Landscape genetics of an endangered lemur (Propithecus tattersalli) within its entire fragmented range

Habitat fragmentation may strongly reduce individuals’ dispersal among resource patches and hence influence population distribution and persistence. We studied the impact of landscape heterogeneity on the dispersal of the golden‐crowned sifaka (Propithecus tattersalli), an endangered social lemur species living in a restricted and highly fragmented landscape. We combined spatial analysis and population genetics methods to describe population units and identify the environmental factors which best predict the rates and patterns of genetic differentiation within and between populations. We used non‐invasive methods to genotype 230 individuals at 13 microsatellites in all the main forest fragments of its entire distribution area. Our analyses suggest that the Manankolana River and geographical distance are the primary structuring factors, while a national road crossing the region does not seem to impede gene flow. Altogether, our results are in agreement with a limited influence of forest habitat connectivity on gene flow patterns (except for North of the species’ range), suggesting that dispersal is still possible today among most forest patches for this species. Within forest patches, we find that dispersal is mainly among neighbouring social groups, hence confirming previous behavioural observations.     

The effect of isolation and history on colonization patterns of plant species in secondary woodland

Colonization success of woodland originating after 1850 was determined for seventeen forest plant species having different dispersal strategies. Colonization rate of the studied endo-and exozoochorous species apparently was considerable higher than that of species having short distance dispersal like myrmecochores and species lacking dispersal mechanisms. The occurrence of eight species in this young forest habitat was related to the distance to the nearest source patch (DNS), as well as to the age of the young patches and to their former land use. DNS calculated to old, existent and occupied source patches affected most analysed species. Only Ilex aquifolium L. had a significant higher occurrence in woodland originating before 1916 than in those originating after 1916. Former land use showed significant effects for three species. Although colonization rate and effects of studied parameters on occurrence were different for the studied species, no clear differences were found between different dispersal groups. The consequences of these results for the understanding of colonization processes of the species studied is discussed.     

The influence of matrix and edges on species richness patterns of ground beetles (Coleoptera: Carabidae) in habitat islands

Aim The aim of this study was to analyse whether, and how, the inclusion of habitat specialists and edge‐preferring species modifies the species–area relationship predictions of the island biogeography theory for an insect group (ground beetles, Coloptera: Carabidae) living in natural fragments. Species–habitat island area relationships applied to terrestrial habitat islands can be distorted by the indiscriminate inclusion of all species occurring in the fragments. Matrices surrounding terrestrial habitat fragments can provide colonists that do not necessarily distinguish the fragment from the matrix and can survive and reproduce there. Edge‐preferring species can further distort the expected relationship, as smaller fragments have larger edge:core ratios. Location Nineteen forest fragments were studied in the Bereg Plain, Hungary, and SW Ukraine. This area contains natural forest patches, mainly of oak and hornbeam, and supports a mountain entomofauna. Methods Ground beetles (Carabidae) present in the 19 forest patches were categorized into generalists, forest specialists and edge‐preferring species. We analysed the relationship between species richness and fragment area using species richness in the different categories. Results The assemblages contained a high share of generalist species (species that occur also in the surrounding matrix). Forest patch size and the number of generalist species showed a marginally significant negative relationship, indicating that generalist species were more important in smaller patches. Forest specialist species richness was correlated positively with patch area. Edge‐preferring species were shown to influence the species–area relationship: the number of edge‐preferring species increased with the edge:area ratio. Main conclusions Both generalist and edge‐preferring species can considerably distort the species–area relationship. Island biogeography theory can be applied to habitat islands only if the habitat islands are defined correctly from the viewpoint of the target species.     

Influence of environmental and spatial variables on regional distribution of forest plant species in a fragmented and changing landscape

During the past several centuries, forests in Europe and large parts of North America have been subject to extensive forest clearance. The last several decades, however, numerous new forest patches have been established onto former agricultural land. As a result, the present forest area often consists of a mixture of small forest patches of different age, area, habitat quality and connectivity embedded within a hostile agricultural landscape. In these patchy landscapes, distribution patterns of plant species may be affected by both regional and local factors, although the relative importance of both is still poorly understood. In this study, we investigated distribution patterns of 113 forest plant species in a fragmented landscape. Species abundances at the regional scale conformed to a clearly unimodal abundance distribution which we believe to be related to 1) environmental heterogeneity due to succession and 2) inequality in migration rates. Patch incidence was significantly related to life form, which in turn was correlated to seed mass and dispersal mechanism. Multiple logistic regressions showed that presence/absence of 59 species studied was significantly affected by patch connectivity, patch area and age for 35, 30 and 34 species, respectively. The results of this study indicate that distribution patterns of forest plant species are influenced by both local and regional factors. Moreover, they also demonstrate that next to spatial aspects of fragmentation, temporal patterns of landscape change may have far-reaching effects on presence/absence patterns of plant species and therefore should be incorporated in studies dealing with regional population structures of plants.     

Fruiting phenology in a tropical dry evergreen forest on the Coromandel coast of India in relation to plant life-forms,physiognomic groups,dispersal modes,and climatic constraints

The fruiting phenology of 22 woody plant species belonging to 19 families was studied with respect to life-forms, physiognomic groups and dispersal modes, for 1 year at monthly intervals, in a tropical dry evergreen forest at Oorani (12°11′N, 79°57′E) on the Coromandel coast of India. At the community level, bimodal fruiting pattern prevailed, with a major peak in the dry season and a minor one in the early rainy season. An annual fruiting pattern was observed in many species and among the studied species fruiting lasted for 2–9 months. There was no significant difference in the frequency of species at three fruiting stages across the life-form categories and many species of upper and lower canopy trees and lianas were in the ripe fruiting phase during the late dry season. Plant physiognomic groups displayed distinct seasonality in fruiting pattern. The fruit maturation period was much longer for the wet season fruiting brevi-deciduous species than evergreen and deciduous species that fruited during the dry season. The variation in timing of fruiting behaviour among zoochorous species demonstrated less seasonality and zoochorous fruits were available throughout the year. Fruiting in anemochorous species peaked during the driest months and dryness favoured the dissemination of seeds. The fruiting patterns observed in the studied tropical dry evergreen forest across various plant traits were comparable with patterns recorded in other tropical seasonal forests.     

Landscape configuration determines gene flow and phenotype in a flightless forest-edge ground-dwelling bush-cricket, Pholidoptera griseoaptera

Spatial configuration of habitats influences genetic structure and population fitness whereas it affects mainly species with limited dispersal ability. To reveal how habitat fragmentation determines dispersal and dispersal-related morphology in a ground-dispersing insect species we used a bush-cricket (Pholidoptera griseoaptera) which is associated with forest-edge habitat. We analysed spatial genetic patterns together with variability of the phenotype in two forested landscapes with different levels of fragmentation. While spatial configuration of forest habitats did not negatively affect genetic characteristics related to the fitness of sampled populations, genetic differentiation was found higher among populations from an extensive forest. Compared to an agricultural matrix between forest patches, the matrix of extensive forest had lower permeability and posed barriers for the dispersal of this species. Landscape configuration significantly affected also morphological traits that are supposed to account for species dispersal potential; individuals from fragmented forest patches had longer hind femurs and a higher femur to pronotum ratio. This result suggests that selection pressure act differently on populations from both landscape types since dispersal-related morphology was related to the level of habitat fragmentation. Thus observed patterns may be explained as plastic according to the level of landscape configuration; while anthropogenic fragmentation of habitats for this species can lead to homogenization of spatial genetic structure.     

Does fragmentation of Urtica habitats affect phytophagous and predatory insects differentially?

Effects of habitat fragmentation on the insect community of stinging nettle (Urtica dioica L.) were studied, using 32 natural nettle patches of different area and degree of isolation in an agricultural landscape. Habitat fragmentation reduced the species richness of Heteroptera, Auchenorrhyncha, and Coleoptera, and the abundance of populations. Habitat isolation and area reduction did not affect all insect species equally. Monophagous herbivores had a higher probability of absence from small patches than all (monophagous and polyphagous) herbivore species, and the percentage of monophagous herbivores increased with habitat area. Abundance and population variability of species were negatively correlated and could both be used as a predictor of the percentage of occupied habitats. Species richness of herbivores correlated (positively) with habitat area, while species richness of predators correlated (negatively) with habitat isolation. In logistic regressions, the probability of absence of monophagous herbivores from habitat patches could only be explained by habitat area (in 4 out of 10 species) and predator absence probability only by habitat isolation (in 3 out of 14 species). Presumably because of the instability of higher-trophic-level populations and dispersal limitation, predators were more affected by habitat isolation than herbivores, while they did not differ from herbivore populations with respect to abundance or variability. Thus increasing habitat connectivity in the agricultural landscape should primarily promote predator populations. Received: 4 February 1998 / Accepted: 4 May 1998     

Habitat connectivity analysis for conservation implications in an urban area

In urbanized areas, habitat loss and fragmentation resulting from urban growth and human activities may threaten the biological diversity. It is essential to maintain the connectivity in some isolated and fragmented habitat patches. In 2005, the orchard-based conservation with the legal binding was implemented in Shenzhen to mitigate the ecological threats from forest destruction and to protect the ecological diversity. It is critical to evaluate the efficiency of orchard habitat from the species’ perspective for providing the reference for the habitat management. Based on graph-theoretic methods, we compared the habitats with or without orchards and evaluated the contribution of orchards to the whole network connectivity and its three fractions (intra, flux and connector), and then analyzed the species that could benefit the most from the habitat supplement. We identified the important landscape elements for serving the prioritized conservation. The results showed that orchard-based conservation was an efficient way in maintaining the functional connectivity, which mainly contributed to the intrapatch connectivity and species dispersal flux. The value of orchard incorporation was strongly related with the dispersal ability of threatened species. Our findings indicated that the orchard conservation would be more valuable for species with relatively weak dispersal abilities. We showed the key patches and links that most contribute to uphold functional connectivity in the reserve network. We believe that the assessment based on habitat functional connectivity can effectively serve the practical guidelines of habitat conservation and management in urban areas.     

Relationships between spatial configuration of tropical forest patches and woody plant diversity in northeastern Puerto Rico

The destruction and fragmentation of tropical forests are major sources of global biodiversity loss. A better understanding of anthropogenically altered landscapes and their relationships with species diversity and composition is needed in order to protect biodiversity in these environments. The spatial patterns of a landscape may control the ecological processes that shape species diversity and composition. However, there is little information about how plant diversity varies with the spatial configuration of forest patches especially in fragmented tropical habitats. The northeastern part of Puerto Rico provides the opportunity to study the relationships between species richness and composition of woody plants (shrubs and trees) and spatial variables [i.e., patch area and shape, patch isolation, connectivity, and distance to the Luquillo Experimental Forest (LEF)] in tropical forest patches that have regenerated from pasturelands. The spatial data were obtained from aerial color photographs from year 2000. Each photo interpretation was digitized into a GIS package, and 12 forest patches (24–34 years old) were selected within a study area of 28 km². The woody plant species composition of the patches was determined by a systematic floristic survey. The species diversity (Shannon index) and species richness of woody plants correlated positively with the area and the shape of the forest patch. Larger patches, and patches with more habitat edge or convolution, provided conditions for a higher diversity of woody plants. Moreover, the distance of the forest patches to the LEF, which is a source of propagules, correlated negatively with species richness. Plant species composition was also related to patch size and shape and distance to the LEF. These results indicate that there is a link between landscape structure and species diversity and composition and that patches that have similar area, shape, and distance to the LEF provide similar conditions for the existence of a particular plant community. In addition, forest patches that were closer together had more similarity in woody plant species composition than patches that were farther apart, suggesting that seed dispersal for some species is limited at the scale of 10 km.     

Species-specific traits predict genetic structure but not genetic diversity of three fragmented Afrotropical forest butterfly species

The Upper Guinean forests of Ghana, West Africa, are considered among the most threatened and fragmented in the world. Little is known about the genetic consequences of fragmentation on Ghana’s forest-associated species, but this genetic signature is generally expected to differ across species. We compared patterns of mtDNA cytochrome oxidase I (COI) variation of three Nymphalid forest butterfly species that differ with respect to their relative dispersibilities (Aterica galene: high habitat fidelity, low dispersal ability; Euphaedra medon: high habitat fidelity, strong dispersal ability; Gnophodes betsimena: relaxed habitat fidelity, low dispersal ability). Individuals were collected from two large forest reserves and five small sacred forest groves. Patterns of differentiation across species were broadly coincident with our predicted hierarchy of relative species dispersibility and suggested that genetic connectivity is most compromised by strict fidelity to forest habitat rather than by raw capacity for sustained flight. Connectivity was uncorrelated with geographic distance, but instead seemed best explained by urbanization and the sequential pattern of forest loss. Genetic diversity was dramatically different among species and not easily explained by either species-specific traits or effects of fragmentation. Aterica galene, the species most impacted by fragmentation, exhibited very high diversity, whereas G. betsimena, a broadly distributed, very common species, with relaxed habitat fidelity, was genetically depauperate. There was limited evidence of genetic erosion from the sacred groves despite these small forest patches accounting for less than 1–10 % of the total area of the forest reserves, which indicates these forest relics have high conservation value.     

Seed dispersal networks in tropical forest fragments: Area effects,remnant species,and interaction diversity

Seed dispersal interactions involve key ecological processes in tropical forests that help to maintain ecosystem functioning. Yet this functionality may be threatened by increasing habitat loss, defaunation, and fragmentation. However, generalist species, and their interactions, can benefit from the habitat change caused by human disturbance while more specialized interactions mostly disappear. Therefore, changes in the structure of the local, within fragment, networks can be expected. Here we investigated how the structure of seed dispersal networks changes along a gradient of increasing habitat fragmentation. We analyzed 16 bird seed dispersal assemblages from forest fragments of a biodiversity-rich ecosystem. We found significant species–, interaction–, and network–area relationships, yet the later was determined by the number of species remaining in each community. The number of frugivorous bird and plant species, their interactions, and the number of links per species decreases as area is lost in the fragmented landscape. In contrast, network nestedness has a negative relationship with fragment area, suggesting an increasing generalization of the network structure in the gradient of fragmentation. Network specialization was not significantly affected by area, indicating that some network properties may be invariant to disturbance. Still, the local extinction of partner species, paralleled by a loss of interactions and specialist–specialist bird–plant seed dispersal associations, suggests the functional homogenization of the system as area is lost. Our study provides empirical evidence for network–area relationships driven by the presence/absence of remnant species and the interactions they perform.     

Assessing the importance of individual habitat patches as irreplaceable connecting elements: An analysis of simulated and real landscape data

Habitat loss and fragmentation are considered to be severe threats to biodiversity, and maintaining natural levels of landscape connectivity may be one of the best responses to these issues. Graph-based habitat availability (reachability) metrics have been shown to be an appropriate method for a multifaceted but coherent landscape connectivity assessment. These metrics can be partitioned into three commensurate fractions (intra, flux, connector) that quantify the different ways in which habitat patches contribute to the overall landscape connectivity and habitat availability. In particular, the connector fraction measures the contribution of patches to the connectivity between other habitat areas as irreplaceable connecting elements or stepping stones. Because many conservation efforts and initiatives are focused on conserving or restoring corridors and other linkages between habitat areas, it is critical to understand more thoroughly the conditions under which investing in these connecting elements is an efficient management strategy. For this purpose, we analysed the contribution of the connector fraction in different simulated habitat patterns under different levels of habitat amount and fragmentation and in natural habitats for endangered forest bird species in Catalonia (Spain). We show that a prominent role of individual stepping stone patches as irreplaceable providers of habitat connectivity and availability arises only under a relatively narrow set of conditions, characterised by low habitat amount, high habitat fragmentation and modest to intermediate species dispersal abilities. We suggest that to support connectivity-related investments, it is necessary to focus on those few species or dispersal distance ranges that are likely to be both most dependent on and most benefited by the conservation or restoration of stepping stone patches. We conclude that the total amount of reachable habitat for a particular species is rarely determined by the contribution of individual connectors as the only dominant factor. Therefore, conservationists should be cautious not to overemphasise the importance of connectivity investments and to balance them with other conservation alternatives and strategies to promote species conservation in heterogeneous landscapes.     

Nest-predation at the edge: an experimental study contrasting two types of edges in the dry Chaco, Paraguay

Forest fragmentation leads to the creation of isolated forest patches with subsequent impact on forest-interior flora and fauna. Forested corridors have been suggested to alleviate some of the impact by increasing the connectivity between remnant forest patches. However, both fragmentation and corridors increase the ratio of edge to core habitat. We studied nest predation of artificial nests at edges between I) contiguous forests and pastures and 2) forested corridors and pastures, in a forest-dominated landscape in the dry Chaco, Paraguay, The aim was lo determine if nest predation was higher near habitat edges compared to within forests and pastures, with special emphasis on edges at forested corridors. We found that predation rates were similar at edges and in interior habitats. Nest predation was higher for both ground and shrub nests in forested areas than in pastures, Predation rates were also higher for both ground and shrub nests at edges along forested corridors compared to edges neighbouring contiguous forests. Forested corridors connecting contiguous forests may thus act as an ecological sink for some species breeding here. Analysis of predator categories revealed that ground nests in pastures were relatively more depredated by mammals and less by birds, compared to both shrub nests in pastures and ground nests in forests.