Landscape composition is the strongest determinant of bird occupancy patterns in tropical forest patches

Context

Biodiversity in tropical region has declined in the last decades, mainly due to forest conversion into agricultural areas. Consequently, species occupancy in these landscapes is strongly governed by environmental changes acting at multiple spatial scales.

Objectives

We investigated which environmental predictors best determines the occupancy probability of 68 bird species exhibiting different ecological traits in forest patches.

Methods.

We conducted point-count bird surveys in 40 forest sites of the Brazilian Atlantic forest. Using six variables related to landscape composition and configuration and local vegetation structure, we predicted the occupancy probability of each species accounting for imperfect detections.

Results

Landscape composition, especially forest cover, best predicted bird occupancy probability. Specifically, most bird species showed greater occupancy probability in sites inserted in more forested landscapes, while some species presented higher occurrence in patches surrounded by low-quality matrices. Conversely, only three species showed greater occupancy in landscapes with higher number of patches and dominated by forest edges. Also, several species exhibited greater occupancy in sites harbouring either larger trees or lower number of understory plants. Of uttermost importance, our study revealed that a minimum of 54% of forest cover is required to ensure high (> 60%) occupancy probability of forest species.

Conclusions

We highlighted that maintaining only 20% of native vegetation in private property according to Brazilian environmental law is insufficient to guarantee a greater occupancy for most bird species. We recommend that policy actions should safeguard existing forest remnants, expand restoration projects, and curb human-induced disturbances to minimise degradation within forest patches.

     

Species Dynamics in Disturbed Landscapes: When does a Shifting Habitat Mosaic Enhance Connectivity?

Although landscape ecology emphasizes the effects of spatial pattern on ecological processes, most neutral models of species–habitat relationships have treated habitat as a static constraint. Do the working hypotheses derived from these models extend to real landscapes where disturbances create a shifting mosaic? A spatial landscape simulator incorporating vegetation dynamics and a metapopulation model was used to compare species in static and dynamic landscapes with identical habitat amounts and spatial patterns. The main drivers of vegetation dynamics were stand-replacing disturbances, followed by gradual change from early-successional to old-growth habitats. Species dynamics were based on a simple occupancy model, with dispersal simulated as a random walk. As the proportion of available habitat (p) decreased from 1.0, species occupancy generally declined more rapidly and reached extinction at higher habitat levels in dynamic than in static landscapes. However, habitat occupancy was sometimes actually higher in dynamic landscapes than in static landscapes with similar habitat amounts and patterns. This effect was most pronounced at intermediate amounts of habitat (p = 0.3?0.6) for mobile species that had high colonization rates, but were unable to cross non-habitat patches. Differences between static and dynamic landscapes were contingent upon the initial metapopulation size and the shapes of disturbances and the resulting habitat patterns. Overall, the results demonstrate that dispersal-limited species exhibit more pronounced critical behavior in dynamic landscapes than is predicted by simple neutral models based on static landscapes. Thus, caution should be exercised in extending generalizations derived from static landscape models to disturbance-driven landscape mosaics.     

Landscape contrast: a solution to hidden assumptions in the metacommunity concept?

The metacommunity concept provides a spatial perspective on community dynamics, and the landscape provides the physical template for a metacommunity. Several aspects of landscape heterogeneity, such as landscape diversity and composition, and characteristics of the matrix between habitat patches such as habitat connectivity, and geometry of habitat patches, may moderate metacommunity processes. These aspects of landscape heterogeneity are rarely considered explicitly in the metacommunity discussion, however. We propose landscape contrast (i.e., the average dissimilarity in habitat quality between neighboring patches) as a key dimension of landscape heterogeneity. The concept of landscape contrast unifies discrete and continuous landscape representations (homogeneous, gradient, mosaic and binary) and offers a means to integrate landscape heterogeneity in the metacommunity concept. Landscape contrast as perceived by the organisms affects several fundamental metacommunity processes and may thus constrain which metacommunity models may be observed. In a review of empirical metacommunity studies (n = 123), only 22 % of studies were explicit about their underlying landscape model assumptions, with striking differences among taxonomic groups. The assumed landscape model constrained, but did not determine, metacommunity models. Integration and explicit investigation of landscape contrast effects in metacommunity studies are likely to advance ecological theory and facilitate its application to real-world conservation problems.     

Influence of patch and landscape characteristics on the distribution of the subterranean rodent <Emphasis Type="Italic">Ctenomys porteousi</Emphasis>

The understanding and prediction of the responses of animal populations to habitat fragmentation is a central issue in applied ecology. The identification of habitat variables associated to patch occupancy is particularly important when habitat quality is affected by human activities. Here, we analyze the influence of patch and landscape characteristics on patch occupancy by the subterranean herbivorous rodent Ctenomys porteousi. Patch occupancy was monitored in a network of 63 habitat patches identified by satellite imagery analysis which extends along almost the whole distributional range for C. porteousi. Suitable habitat for the occurrence of C. porteousi is highly fragmented and represents <10% of the total area in its distributional range. The distribution of C. porteousi in the patch network is affected not only by characteristics of the habitat patches, but also by those of the surrounding landscape matrix. Significant differences between occupied and empty patches were found in several environmental variables. Overall, occupied patches were larger, less vegetated, more connected, and had larger neighbor patches than empty patches. A stepwise procedure on a generalized linear model selected four habitat variables that explain patch occupancy in C. porteousi; it included the effects of habitat quality in the matrix surrounding the patch, average vegetation cover in the patch, minimum vegetation cover in the matrix surrounding the patch, and the area of the nearest neighbor patch. These results indicate that patch occupancy in C. porteousi is strongly influenced by the availability and quality of habitat both in the patch and in the surrounding landscape matrix.     

Quantifying determinants contributing to plant species richness in mosaic landscapes: a single- and multi-patch perspective

Despite good theoretical knowledge about determinants of plant species richness in mosaic landscapes, validations based on complete surveys are scarce. We conducted a case study in a highly fragmented, traditional agricultural landscape. In 199 patches of 20 representative multi-patch-plots (MPPs, 1 ha) we recorded a total of 371 plant species. In addition to an additive partitioning of species diversity at the (a) patch- and (b) MPP-scale, we adopted the recently proposed ‘specificity’ measure to quantify the contribution of a spatial subunit to landscape species richness (subunit-to-landscape-contribution, SLC). SLC-values were calculated at both scales with respect to various spatial extents. General regression models were used to quantify the relative importance of hypothesis-driven determinants for species richness and SLC-values. At the patch scale, habitat type was the main determinant of species richness, followed by area and elongated shape. For SLC-values, area was more important than habitat type, and its relevance increased with the extent of the considered landscape. Influences of elongated shape and vegetation context were minor. Differences between habitat types were pronounced for species richness and also partly scale-dependent for SLC-values. Relevant predictors at the MPP-scale were nonlinear habitat richness, the gradient from anthropogenic to seminatural vegetation, and the proportions of natural vegetation and rare habitats. Linear elements and habitat configuration did not contribute to species richness and SLC. Results at the MPP-scale were in complete accordance with the predictions of the mosaic concept. Hence, our study represents its first empirical validation for plant species diversity in mosaic landscapes.     

Successional change in the insect community of a fragmented landscape

Habitat fragmentation strongly affects insect species diversity and community composition, but few studies have examined landscape effects on long term development of insect communities. As mobile consumers, insects should be sensitive to both local plant community and landscape context. We tested this prediction using sweep-net transects to sample insect communities for 8 years at an experimentally fragmented old-field site in northeastern Kansas, USA. The site included habitat patches undergoing secondary succession, surrounded by a low turf matrix. During the first 5 years, plant richness and cover were measured in patches. Insect species richness, total density, and trophic diversity increased over time on all transects. Cover of woody plants and perennial forbs increased each year, adding structural complexity to successional patches and potentially contributing to increased insect diversity. Within years, insect richness was significantly greater on transects through large successional patches (5000 m²) than on transects through fragmented arrays of 6 medium-sized (total area 1728 m²) or 15 small (480 m²) patches. However, plant cover did not differ among patch types and was uncorrelated with insect richness within years. Insect richness was strongly correlated with insect density, but trophic and α diversities did not differ among patch types, indicating that patch insect communities were subsets of a common species pool. We argue that differences in insect richness resulted from landscape effects on the size of these subsets, not patch succession rates. Greater insect richness on large patches can be explained as a community-level consequence of population responses to resource concentration.     

Wetland hydrology,area, and isolation influence occupancy and spatial turnover of the painted turtle, <Emphasis Type="Italic">Chrysemys picta</Emphasis>

Habitat area and isolation have been useful predictors of species occupancy and turnover in highly fragmented systems. However, habitat quality also can influence occupancy dynamics, especially in patchy systems where habitat selection can be as important as stochastic demographic processes. We studied the spatial population dynamics of Chrysemys picta (painted turtle) in a network of 90 wetlands in Illinois, USA from 2007 to 2009. We first evaluated the relative influence of metapopulation factors (area, isolation) and habitat quality of focal patches on occupancy and turnover. Next, we tested the effect of habitat quality of source patches on occupancy and turnover at focal patches. Turnover was common with colonizations (n = 16) outnumbering extinctions (n = 10) between the first 2 years, and extinctions (n = 16) outnumbering colonizations (n = 3) between the second 2 years. Both metapopulation and habitat quality factors influenced C. picta occupancy dynamics. Colonization probability was related positively to spatial connectivity, wetland area, and habitat quality (wetland inundation, emergent vegetation cover). Extinction probability was related negatively to wetland area and emergent vegetation cover. Habitat quality of source patches strongly influenced initial occupancy but not turnover patterns. Because habitat quality for freshwater turtles is related to wetland hydrology, a change from drought to wet conditions during our study likely influenced distributional shifts. Thus, effects of habitat quality of source and focal patches on occupancy can vary in space and time. Both metapopulation and habitat quality factors may be needed to understand occupancy dynamics, even for species exhibiting patchy population structures.     

Surface metrics: an alternative to patch metrics for the quantification of landscape structure

Modern landscape ecology is based on the patch mosaic paradigm, in which landscapes are conceptualized and analyzed as mosaics of discrete patches. While this model has been widely successful, there are many situations where it is more meaningful to model landscape structure based on continuous rather than discrete spatial heterogeneity. The growing field of surface metrology offers a variety of surface metrics for quantifying landscape gradients, yet these metrics are largely unknown and/or unused by landscape ecologists. In this paper, we describe a suite of surface metrics with potential for landscape ecological application. We assessed the redundancy among metrics and sought to find groups of similarly behaved metrics by examining metric performance across 264 sample landscapes in western Turkey. For comparative purposes and to evaluate the robustness of the observed patterns, we examined 16 different patch mosaic models and 18 different landscape gradient models of landscape structure. Surface metrics were highly redundant, but less so than patch metrics, and consistently aggregated into four cohesive clusters of similarly behaved metrics representing surface roughness, shape of the surface height distribution, and angular and radial surface texture. While the surface roughness metrics have strong analogs among the patch metrics, the other surface components are largely unique to landscape gradients. We contend that the surface properties we identified are nearly universal and have potential to offer new insights into landscape pattern–process relationships. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structure of plant communities and landscape patterns in alluvial meadows of two flood plains in the north-east of France

Flood frequency and agricultural pressure can effect pattern and diversity in the plant communities and the landscape of flood plain meadows. The flood plains of north-east France are valuable semi- natural ecosystems with a high diversity of plants. This study was carried out in two valleys with plant communities showing the same zonation along a moisture gradient. About 350 measurements in each valley were carried out on 50 m2 sampling sites. Two study areas were intensively measured within each of the two valleys (1300 ha in total). Hydrological, geological and human factors have determined the unique landscape pattern of each valley. Using vegetation maps (1/5000) of the two valleys, landscape structure in terms of the size, number and form of patches were compared and the characteristics of the disturbance regimes (natural and human disturbance) creating each landscape are analysed. Variations of landscape indices are discussed in relation to the increase in agricultural pressure. Using quantitative parameters of landscape ecology to analyse vegetation mosaics provides an assessment of agricultural pressure and natural constraints on the flood plain scale. Agricultural intensification led to a decrease of meadow complexity whose natural rough shapes are made straight. Moreover flooded meadows lost thus natural connectivity with ditches and river which determined biodiversity and ecological processes of flood plains.     

Longitudinal- and transverse-scale environmental influences on riparian vegetation across multiple levels of ecological organization

Riparian vegetation is distinct from adjacent upland terrestrial vegetation and its distribution is affected by various environmental controls operating at the longitudinal scale (along the river) or transverse scale (perpendicular to the river). Although several studies have shown how the relative importance of transverse or longitudinal influences varies with the scale of observation, few have examined how the influences of the two scales vary with the level of ecological organization. We modeled vegetation-environment relationships at three hierarchically nested levels of ecological organization: species, plant community, and vegetation type. Our hierarchically structured analyses differentiated the spatial extent of riparian zones from adjacent upland vegetation, the distribution of plant community types within the riparian zone, and the distribution of plant species within community types. Longitudinal gradients associated with climate and elevation exerted stronger effects at the species level than at the community level. Transverse gradients related to lateral surface water flux and groundwater availability distinguished riparian and upland vegetation types, although longitudinal gradients of variation better predicted species composition within either riparian or upland communities. We concur with other studies of riparian landscape ecology that the relative predictive power of environmental controls for modeling patterns of biodiversity is confounded with the spatial extent of the study area and sampling scheme. A hierarchical approach to spatial modeling of vegetation-environment relationships will yield substantial insights on riparian landscape patterns.     

Landscape structure and the disturbance regime at three rural regions in Hiroshima Prefecture,Japan

Using the vegetation maps of island, inland and mountainous rural regions in Hiroshima Prefecture in western Japan, landscape structures in terms of the size and number of patches are compared, and the characteristics of the disturbance regimes creating each landscape are discussed. Landscape structure in the island rural region is the most heterogeneous, because factors which alter the landscape structure are the most complex. This heterogeneity is established and kept by the agricultural land uses and natural disturbances such as forest fire and pine-disease. At the mountainous rural region, the landscape mosaic is characterized by the relatively large patches composed of conifer plantations and secondary deciduous oak forests. This is the result of the forestry. The inland region landscape is the most homogeneous, because factors which alter landscape structure are now absent. The complex of the physical, biological and anthropogenic forces makes the landscape unique to each region.     

The plant functional traits that explain species occurrence across fragmented grasslands differ according to patch management,isolation, and wetness

Context

Landscape fragmentation significantly affects species distributions by decreasing the number and connectivity of suitable patches. While researchers have hypothesized that species functional traits could help in predicting species distribution in a landscape, predictions should depend on the type of patches available and on the ability of species to disperse and grow there.

Objectives

To explore whether different traits can explain the frequency of grassland species (number of occupied patches) and/or their occupancy (ratio of occupied to suitable patches) across a variety of patch types within a fragmented landscape.

Methods

We sampled species distributions over 1300 grassland patches in a fragmented landscape of 385 km² in the Czech Republic. Relationships between functional traits and species frequency and occupancy were tested across all patches in the landscape, as well as within patches that shared similar management, wetness, and isolation.

Results

Although some traits predicting species frequency also predicted occupancy, others were markedly different, with competition- and dispersal-related traits becoming more important for occupancy. Which traits were important differed for frequency and occupancy and also differed depending on patch management, wetness, and isolation.

Conclusions

Plant traits can provide insight into plant distribution in fragmented landscapes and can reveal specific abiotic, biotic, and dispersal processes affecting species occurrence in a patch type. However, the importance of individual traits depends on the type of suitable patches available within the landscape.

     

Threshold levels of habitat composition for the presence of the long-tailed tit (Aegithalos caudatus) in a boreal landscape

We assessed the habitat patch occupancy of a deciduous-mixed forest specialist, the long-tailed tit (Aegithalos caudatus), in a 1000 km² conifer dominated landscape in relation to two landscape parameters, namely proportion and isolation of suitable habitat. Data from five consecutive spring seasons were used and within habitat variation controlled for. The occurrence of long-tailed tits was positively related to the amount of habitat within 1 km² (p=0.0007) and negatively related to the distance between habitat patches (p<0.0001). When combined, the two variables explained >78% of the variation in local patch occupancy. There were distinct thresholds in these landscape variables for the probability of local long-tailed tit presence. In the model the probability increased from 0.1 to 0.8 when interpatch distance decreased from 500 to 100 m with 5% total habitat coverage. With a total proportion of 15% suitable habitat, the same probability jump occurred when interpatch distance changed from 900 to 500 m. The general importance of defined measurements and quantified threshold levels for species conservation and landscape management is discussed.     

Matrix is important for mammals in landscapes with small amounts of native forest habitat

Acknowledgment that the matrix matters in conserving wildlife in human-modified landscapes is increasing. However, the complex interactions of habitat loss, habitat fragmentation, habitat condition and land use have confounded attempts to disentangle the relative importance of properties of the landscape mosaic, including the matrix. To this end, we controlled for the amount of remnant forest habitat and the level of fragmentation to examine mammal species richness in human-modified landscapes of varying levels of matrix development intensity and patch attributes. We postulated seven alternative models of various patch habitat, landscape and matrix influences on mammal species richness and then tested these models using generalized linear mixed-effects models within an information theoretic framework. Matrix attributes were the most important determinants of terrestrial mammal species richness; matrix development intensity had a strong negative effect and vegetation structural complexity of the matrix had a strong positive effect. Distance to the nearest remnant forest habitat was relatively unimportant. Matrix habitat attributes are potentially a more important indicator of isolation of remnant forest patches than measures of distance to the nearest patch. We conclude that a structurally complex matrix within a human-modified landscape can provide supplementary habitat resources and increase the probability of movement across the landscape, thereby increasing mammal species richness in modified landscapes.     

Patterns of habitat occupancy, genetic variation and predicted movement of a flightless bush cricket, Pholidoptera griseoaptera, in an agricultural mosaic landscape

Habitat fragmentation has been generally regarded detrimental to the persistence of many species, especially those with limited dispersal abilities. Yet, when exactly habitat elements become functionally disconnected very much depends on the dispersal ability of a species in combination with the landscape’s composition in which it occurs. Surprisingly, for many small and ground-walking generalists knowledge at what spatial scale and to what extent landscape structure affects dispersal is very scarce. Because it is flightless, the bush cricket Pholidoptera griseoaptera may be regarded susceptible to fragmentation. We applied habitat occupancy surveys, population genetic analyses and movement modelling to investigate the performance of P. griseoaptera in an agricultural mosaic landscape with suitable habitat patches of varying size and isolation. Despite its presumed dispersal limitation we could show that P. griseoaptera occupied the majority of suitable habitats, including small and isolated patches, showed a very low and non-significant genetic differentiation (F _ST = 0.0072) and, in the model, managed to colonize around 73% of all suitable habitat patches within one generation under weak and strong landscape-effect scenarios. We conclude that P. griseoaptera possesses the behavioural attributes (frequent inter-patch dispersal) necessary to persist in this landscape characterized by a patchy distribution of habitat elements. Yet, sound recommendations to landscape planning and conservation require more research to determine whether this represents a general behaviour of the species or a behavioural adaptation to this particular landscape.     

Landscape fragmentation,land-use legacy and propagule pressure promote plant invasion on coastal dunes: a patch-based approach

Coastal dunes and sand areas are reported to be among the habitats most invaded by alien species in Europe. Landscape pattern could be a significant driver in invasion processes in parallel with land-use legacy. Fragmentation of natural habitats combined with the availability of propagules from the surrounding matrix may enhance the invisibility of ecological communities. Based on multitemporal land cover maps (1954–2008) and a floristic database, we analyzed how habitat fragmentation, propagule pressure and land-use legacy have affected alien plants’ presence and richness on natural dune patches along the Lazio Coast (Central Italy). Floristic data were derived from an existing geo-database of random vegetation plots (64 m²). A set of landscape patch-based metrics, considered to be adequate proxies of the main processes affecting alien invasion and richness, was calculated. First, we fit a generalized linear model (GLM) with binomial errors to assess which landscape metrics are influencing patch invasion. Second, we extracted invaded patches and, with GLMs, we investigated how landscape metrics affect average alien species richness. Alien invasion and alien richness seem to be affected by different processes: although alien invasion of each patch is strongly associated with its land-use legacy, the richness of aliens is more affected by landscape fragmentation and by the propagule pressure to which patch is exposed. By integrating spatial and temporal landscape metrics with floristic data, we were able to disentangle the relations of landscape fragmentation, propagule pressure and land-use legacy with the presence and richness of alien plants. The methodological approach here adopted could be easily extended to other alien species and ecosystems, offering scientifically sound support to prevent the high economic costs derived from both the control and the eradication of aliens.     

Small urban woodlands as biodiversity conservation hot-spot: a multi-taxon approach

To evaluate the importance of urban woodlands to serve as potential sites for biodiversity conservation, we analysed bird, carabid beetle and small mammal community responses to urbanisation at different spatial scales. We analysed the relationships between the variations of the structure (species richness S, diversity H′ and dominance D) of animal communities of woodlands distributed along a rural–urban gradient, and the variations along this same gradient of (1) the vegetation within woodlands, (2) the landscape at 100 m and (3) 600 m around the woodlands. We identified the spatial scales whose variations along the gradient most affected each animal community structure, and characterised community responses to these variations. Our results showed that urbanisation affected taxa differently according to their dispersal ability. Carabid beetles, less mobile, seem to be sensitive to increasing fragmentation and built surfaces from periurban to town centre which could make their movement within the urban landscape difficult. Birds, mobile species, seem to be more sensitive to variations of the vegetation structure within woodlands from periurban to town centre that could affect their capacity to maintain in habitat patches. Although our study did not allow relating the small mammal community structure to urbanisation, it suggests that this taxa is sensitive to urban local disturbances. A relevant management scale of woodlands can be specified for each taxa conservation. Urban woodlands accommodate over 50% of the species present in periurban woodlands, and effective management could enhance this number. Woodlands seem to be a good choice for promoting biodiversity conservation in towns.     

Vegetation complexes of flowing-water habitats and their importance for the differentiation of landscape units

An inductive method for recognizing vegetation complexes is presented. These complexes can be used to define landscape units. The method is demonstrated with regard to the river and rivulet valleys of the Black Forest in south-western Germany. It is based on surveys of locally occurring plant communities in homogeneous landscape units, using a cover-abundance scale for the areal extension of each community. The communities have first been established on the basis of the usual relevés of small homogeneous plots.The surveys are called sigma relevés (sigma = Greek for sum), Sigma relevés can be arranged in tables by the usual classification method in order to establish vegetation complexes. Characteristic and differential communities can be elaborated to characterize the vegetation complexes. The specific spatial distribution of each complex reflects certain physical-geographical and anthropo-geographical characteristics. Some applied aspects can be included for each vegetation complex, for example, lists of woody species typical for a landscape unit. From the point of view of water economy such a survey is useful since many efforts are being made to plant woody species in accordance with natural conditions along river and rivulet embankments.