Negative Effects Of Habitat Fragmentation Research Articles

Construction of ecological network based on habitat risks identifying by points of interest: A case study of Wuhan Metropolitan Area.

Ecological network construction plays a key role in ecological restoration, which can effectively mitigate negative effects of habitat fragmentation on biodiversity. Here, we proposed an improved analytical framework for ecological network identification. Specifically, ecological sources were identified using a three-dimension indicator system in terms of form, quality and functions of habitats. Ecological resistance surfaces were determined based on the incorporation of points of interest data that could characterize human activities into habitat risk assessment (HRA) model, while ecological corridors were extracted using circuit theory approach. With Wuhan Metropolitan Area as a case, we explored the key points and structures of ecological network. Moreover, we compared the construction method of ecological resistance surface based on points of interest and HRA model with traditional methods that determined by land use types and by traditional HRA model, to validate the proposed framework. The results showed that the ecological source area of Wuhan Metropolitan Area was 15200 km2, the length of ecological corridor was 1956.68 km, and that there were 87 ecological "pinch points" and 67 ecological barrier points. Compared with traditional methods, the material circulation, network complexity, and ecological connectivity of the ecological network identified by the improved framework were significantly improved, with network closure, dot-line ratio, and network connectivity being increased by 61.5%, 28.1% and 28.7% on average. The identified ecological "pinch points" and barrier points could provide precise decision-making support for ecological restoration and conservation.

Transient effects of corridors on polygyne fire ants over a decade

Abstract Although corridors are frequently regarded as a way to mitigate the negative effects of habitat fragmentation, concerns persist that corridors may facilitate the spread of invasive species to the detriment of native species. The invasive fire ant, Solenopsis invicta, has two social forms. The polygyne form has limited dispersal abilities relative to the monogyne form. Our previous work in a large‐scale corridor experiment showed that in landscapes dominated by the polygyne form, fire ant density was higher and native ant species richness was lower in habitat patches connected by corridors than in unconnected patches. We expected that these observed corridor effects would be transient, that is, that fire ant density and native ant species richness differences between connected and unconnected patches would diminish over time as fire ants eventually fully established within patches. We tested this prediction by resampling the three landscapes dominated by polygyne fire ants 6 to 11 years after our original study. Differences in fire ant density between connected and unconnected habitat patches in these landscapes decreased, as expected. Differences in native ant species richness were variable but lowest in the last 2 years of sampling. These findings support our prediction of transient corridor effects on this invasive ant and stress the importance of temporal dynamics in assessing population and community impacts of habitat connectivity.

Invasive Alien Plant Species—Raising Awareness of a Threat to Biodiversity and Ecological Connectivity (EC) in the Adriatic-Ionian Region

Improving ecological connectivity (EC) within landscapes by establishing corridors and ecological networks has been proposed to counteract the negative effects of habitat fragmentation and climate change on biodiversity. To be functional, ecological networks should be kept free of opportunistic invasive species that can disrupt EC between protected areas and cause biodiversity loss. The present study focused on perennial herbaceous species whose occurrence in the Adriatic-Ionian region has increased in the last two decades, namely common milkweed (Asclepias syriaca), Jerusalem artichoke (Helianthus tuberosus), Japanese knotweed (Reynoutria japonica), Bohemian knotweed (Reynoutria × bohemica), giant hogweed (Heracleum mantegazzianum), giant goldenrod (Solidago gigantea), Canadian goldenrod (Solidago canadensis), and Bermuda buttercup (Oxalis pes-caprae). All species have a high potential to spread in grasslands, abandoned agricultural fields, forest edges, and riparian areas and pose a significant threat to native plant communities and biodiversity. Restoring heavily infested sites is a major challenge because these perennial invaders are very persistent and tend to alter the soil environment in invaded habitats and prevent the recolonization of native plant communities. Therefore, early action should be taken to prevent the spread of these environmental weeds in ecological networks and protected areas with high conservation value.

Landscape connectivity for the invisibles

Because of land use changes, a worldwide decrease in biodiversity is underway, mostly driven by habitat degradation and fragmentation. Increasing landscape connectivity (i.e. the degree to which the landscape facilitates movement between habitat patches) has been proposed as a key landscape‐level strategy to counterbalance the negative effects of habitat fragmentation. A robust theoretical and methodological framework has been developed for the concept of connectivity, and an increasing body of empirical evidence supports the relevance of connectivity for biodiversity. However, the framework was built ignoring species that represent the dominant proportion of biodiversity on earth: microorganisms. The extent to which the existing conceptual and methodological frameworks on connectivity can be applied to microorganisms remain unknown. We reviewed existing evidence and analyzed methods to test the influence of connectivity on microorganisms. We included all types of microorganisms, from symbiotic to pathogenic and free‐living microorganisms, across all ecosystems. We describe the effect of connectivity on microorganism populations and communities, and identify the limitations and large gaps in current knowledge. Microorganisms can differ from macroorganisms in their response to connectivity due to short (distance less than a meter) dispersal distance of some groups, longer time lag of microorganisms response (possibly accompanied by evolutionary processes) and host association. The latter relies on tight interactions and feedback effects that drive microbial‐landscape relationships and lead to possible coadaptation processes. Incorporating the connectivity concept in microbial community assembly rules to preserve the diversity of microbial communities and the ecosystem services they provide could be a crucial step forward in the face of pressing global changes.

Corridors as a tool for linking habitats – Shortcomings and perspectives for plant conservation

Habitat fragmentation and isolation are considered important causes of biodiversity loss in cultural landscapes. To counter the negative effects of fragmentation such as reduced connectivity and increased risks of population extinction due to stochastic processes and genetic erosion, it has been proposed to establish linear ecological corridors to facilitate dispersal between isolated habitat patches. We summarise the current knowledge on the potential benefits and limitations of corridors for reducing the negative effects of habitat fragmentation on plant populations. We address the opportunities and problems that are associated with linear corridors and advocate the use of semi-open corridors as an alternative that might overcome some shortcomings of conventional corridors for plants. Observational and experimental studies have found that various types of linear corridors can increase plant dispersal. Other linear structures such as paths, roads, railways and streams may also function to a certain extent as corridors, although mostly for widespread species. Because plants are highly dependent on external agents such as animals or wind to reach new habitats, the effectivity of corridors is strongly influenced by their structural features and suitability for animal dispersers. However, many plant species can only use corridors for long-distance dispersal if they can also use them as stepping stone habitats where they can establish, grow, reproduce and then disperse further. This dispersal critically depends on suitable light conditions and disturbance regimes, and on a sufficient width of a corridor to reduce edge effects. Thus, hedgerows appear to be suitable corridors for some forest species but are too narrow for forest specialists from the interior of woodlands. Corridors do not only have positive effects but may also facilitate the spread of invasive species. Moreover, a potentially underestimated negative effect of linear corridors is that they may actually create new dispersal barriers when they intersect other habitats. For example, linear woodland corridors that intersect grasslands may successfully connect patches of woodland but simultaneously form strong barriers for grassland species and increase the fragmentation of their populations. As an alternative to linear corridors, we recommend “semi-open corridors” that simultaneously connect patches of both open habitats and woodlands and promote the dispersal of species of both types of habitat. This idea is based on the various types of semi-open landscapes in Europe that have been formed by grazing with livestock, resulting in a mosaic of open habitats, groups of trees or shrubs and small woodland patches, and are characterised by a high diversity of environmental conditions on a small scale. Wide corridors of such semi-open habitats may avoid the strong edge and barrier effects associated with linear corridors and provide suitable stepping stone habitats for species with different habitat requirements.

The Habitat Amount Hypothesis implies negative effects of habitat fragmentation on species richness

AbstractThe habitat amount hypothesis (HAH) predicts that species richness in a habitat site increases with the amount of habitat in the ‘local landscape’ defined by an appropriate distance around the site, with no distinct effects of the size of the habitat patch in which the site is located. It has been stated that a consequence of the HAH, if supported, would be that it is unnecessary to consider habitat configuration to predict or manage biodiversity patterns, and that conservation strategies should focus on habitat amount regardless of fragmentation. Here, I assume that the HAH holds and apply the HAH predictions to all habitat sites over entire landscapes that have the same amount of habitat but differ in habitat configuration. By doing so, I show that the HAH actually implies clearly negative effects of habitat fragmentation, and of other spatial configuration changes, on species richness in all or many of the habitat sites in the landscape, and that these habitat configuration effects are distinct from those of habitat amount in the landscape. I further show that, contrary to current interpretations, the HAH is compatible with a steeper slope of the species–area relationship for fragmented than for continuous habitat, and with higher species richness for a single large patch than for several small patches with the same total area (SLOSS). This suggests the need to revise the ways in which the HAH has been interpreted and can be actually tested. The misinterpretation of the HAH has arisen from confounding and overlooking the differences in the spatial scales involved: the individual habitat site at which the HAH gives predictions, the local landscape around an individual site and the landscapes or regions (with multiple habitat sites and different local landscapes) that need to be analysed and managed. The HAH has been erroneously viewed as negating or diminishing the relevance of fragmentation effects, while it actually supports the importance of habitat configuration for biodiversity. I conclude that, even in the cases where the HAH holds, habitat fragmentation and configuration are important for understanding and managing species distributions in the landscape.

Species turnover and low stability in a community of euglossine bees (Hymenoptera: Apidae) sampled within 28 years in an urban forest fragment

Orchid bees are important long-distance pollinators in Neotropical rainforests. Despite their great flight capacity, some species avoid leaving the forest and might be then more vulnerable to the negative effects of habitat fragmentation. Here, we sampled the euglossine fauna from a forest fragment in an urban zone and compared the data to two surveys conducted in the same area 28 and 20 years before. Twelve species were sampled, and the highest values of both abundance and richness were recorded in the present sampling. Species turnover was observed with the resilient species Euglossa cordata and Eulaema nigrita presenting a high increase in number over the years whereas the prevalent species in the former samplings, Euglossa pleosticta, show the highest stable populations. Conversely, the abundance of Euglossa annectans decreased until zero in the last sampling. The studied orchid bee populations had a lower stability value when compared with other euglossine long-term surveys. Our results indicate that even a small forest fragment within an urbanised landscape and subjected to different levels of anthropogenic impacts harbours a diverse euglossine fauna. It is suggested that not only the preservation and maintenance of forest fragments in urban areas but also its restoration after environmental impacts are important procedures to support species-rich wildlife.

Combining habitat suitability models and spatial graphs for more effective landscape conservation planning: An applied methodological framework and a species case study

In response to the negative effects of habitat fragmentation on biodiversity, habitat network conservation and restoration has become a central objective in conservation planning. Evaluating landscape functional connectivity and mapping habitat networks are key steps for implementing effective actions, but both remain challenging. Habitat suitability models (HSM) and spatial graphs provide conservation managers with useful information for landscape planning. To tackle their respective drawbacks, we proposed to combine HSM and spatial graphs in a four-step methodological framework: (i) collect and prepare input data; (ii) model habitat suitability using MaxEnt to map the species’ habitat suitability index (HSI); (iii) transform the HSI map into spatial graph inputs using GIS; and, (iv) perform spatial graph connectivity analysis using Graphab. The outputs of this species-specific and quantitative approach were maps of the species’ habitat network. Habitat patches and dispersal linkages were ranked according to their importance for overall habitat availability and landscape connectivity. This prioritization identified locations where conservation biologists and landscape planners should focus conservation and restoration efforts. This framework is illustrated here with a case study on the woodlark (Lullula arborea) - a bird species - in a French Mediterranean area, and the method’s limitations and alternatives are discussed. The quantitative-based graphical outputs of the framework can valuably support decision-making for landscape planning, complement local expert opinion, and encourage appropriate stakeholders to cooperate at regional scale.

Connectivity increases trophic subsidies in fragmented landscapes

Landscape corridors mitigate the negative effects of habitat fragmentation by increasing dispersal. Corridors also increase biodiversity in connected habitat fragments, suggestive of metacommunity dynamics. What is unknown in this case is the mechanisms through which metacommunity dynamics act. Working in a large-scale fragmentation experiment, we tested the effect of corridors on the movement of prey species and subsequent effects on predator nutrition (which we call trophic subsidies). We enriched plants of central patches with 15 N, then measured δ15 N in green lynx spiders, the most abundant insect predator, in patches that were either connected to or isolated from the enriched patch. We found that corridors increased prey movement, as they increased spider δ15 N by 40% in connected patches. Corridors also improved spider body condition, increasing nitrogen relative to carbon. We suggest a novel mechanism, trophic subsidies, through which corridors may increase the stability or size of populations in connected landscapes.

The negative effects of habitat fragmentation operate at the scale of dispersal.

Habitat loss is often considered the greatest near-term threat to biodiversity. Yet the impact of habitat fragmentation, or the change in habitat configuration for a given amount of habitat loss, has been intensely debated. We isolated effects of habitat loss from fragmentation on the demography, movement, and abundance of wild populations of a specialist herbivore, Chelinidea vittiger, by removing 2,088 patches across 15 landscapes. We compared fragmentation resulting from random loss, which is often considered in theory, to aggregated loss, which is often observed in the real world. When quantifying fragmentation caused by random vs. aggregated loss, aggregated loss led to less fragmented landscapes than random loss based on patch isolation, but more fragmented landscapes when based on isolation at a larger mesoscale scale defined by dispersal distances of C.vittiger. Overall, habitat loss decreased population size and demographic parameters, with thresholds occurring at approximately 70-80% patch loss. Synergistic effects also occurred, where an aggregated pattern of loss had negative effects at low, but not high, amounts of habitat loss. Effects on population size of C.vittiger were driven by reductions in movement and subsequent reproduction. The direction of habitat fragmentation effects from random and aggregated loss treatments, for a given habitat amount, was conflictingly positive or negative depending on the scale at which fragmentation was quantified. Fragmentation quantified at the scale of dispersal for this species best explained population size and highlighted that fragmentation had negative effects at a mesoscale. Our results emphasize the importance of quantifying habitat fragmentation at biologically appropriate scales.

Fragmentation alters home range and movements of the Dunes Sagebrush Lizard (Sceloporusarenicolus)

Habitat fragmentation is a major driver of biodiversity loss and among reptiles has been attributed as a cause of species decline. The negative effect of habitat fragmentation has also been shown to be worse for species that are habitat specialists. The Dunes Sagebrush Lizard (Sceloporus arenicolus Degenhardt and Jones, 1972) is a species that specializes on the shinnery oak (Quercus havardii Rydb.) sand-dune landform of the Mescalero–Monahans Sandhills ecosystem in western Texas and eastern New Mexico, USA. This landform has been fragmented by roads and well pads used for the extraction of oil and gas resources. The effects of fragmentation on the home range and movements of this species can lead to the effective isolation of populations and increased risk of localized extirpations. We showed that home-range size was larger in an unfragmented area and that the mean distance of movements was greater. We also observed that roads in the fragmented areas restricted movements of S. arenicolus. We concluded that roads can be barriers to movements even though only narrow strips of habitat are altered.

High cover of forest increases the abundance of most grassland butterflies in boreal farmland

Abstract High cover of forest in the landscape matrix has been shown to weaken the negative effects of habitat fragmentation on grassland butterflies. No studies have however focused on examining species‐specific responses of grassland butterflies to forest. The data from 3 years of butterfly monitoring in Southern Finland were used to test whether the amount of forest cover in the surrounding landscape affected the abundance of grassland butterfly species in semi‐natural grasslands, field margins, and forest edges. More than half of the studied species benefitted from high cover of forest. Species with the strongest preference for forested landscapes were Lycaena virgaureae, Argynnis adippe, Argynnis aglaja, and Boloria selene, which probably find suitable resources in herbaceous habitats at forest edges and clearings. Several small‐sized species were positively affected by surrounding forest cover in field margins but not in the other habitat types. Although field margins are suboptimal habitats for grassland butterflies, they provide important corridors for dispersal. High cover of forest in the landscape matrix may enhance butterfly dispersal along field margins by reducing windiness, which is likely to be most important for small‐sized species with poor dispersal capacity. The most abundant grassland species showed little or no preference for forested landscapes. Our results suggest that high cover of forest enhances the persistence of most grassland butterflies, including declining species, in boreal agricultural landscapes. The responses to forest are however strongly dependent on species‐specific properties and habitat types.

Responses of insect herbivores and herbivory to habitat fragmentation: a hierarchical meta-analysis.

Loss and fragmentation of natural habitats can lead to alterations of plant-animal interactions and ecosystems functioning. Insect herbivory, an important antagonistic interaction is expected to be influenced by habitat fragmentation through direct negative effects on herbivore community richness and indirect positive effects due to losses of natural enemies. Plant community changes with habitat fragmentation added to the indirect effects but with little predictable impact. Here, we evaluated habitat fragmentation effects on both herbivory and herbivore diversity, using novel hierarchical meta-analyses. Across 89 studies, we found a negative effect of habitat fragmentation on abundance and species richness of herbivores, but only a non-significant trend on herbivory. Reduced area and increased isolation of remaining fragments yielded the strongest effect on abundance and species richness, while specialist herbivores were the most vulnerable to habitat fragmentation. These fragmentation effects were more pronounced in studies with large spatial extent. The strong reduction in herbivore diversity, but not herbivory, indicates how important common generalist species can be in maintaining herbivory as a major ecosystem process.

Taxonomic and functional divergence of tree assemblages in a fragmented tropical forest.

Tropical forests are being exposed to increasing levels of habitat loss and fragmentation, threatening the maintenance of global biodiversity. However, the effect that land-use change may have on the spatial dissimilarities in taxonomic and functional composition of remaining assemblages (i.e., taxonomic/functional β-diversity) remains poorly understood. We examined a large vegetation database from an old and severely fragmented Atlantic forest landscape to test two alternative hypotheses: (1) tree assemblages experience a taxonomic and functional homogenization (reduced β-diversity) between forest fragments and along forest edges, or alternatively, (2) these edge-affected forests show increased taxonomic and functional differentiation (increased β-diversity) when compared to forest interior (reference) stands. Taxonomic and functional β-diversity were examined via novel abundance-based metrics and considering functional traits related to plant dispersion, recruitment, and growth. Overall, taxonomic β-diversity among fragments was significantly higher than among edge and reference plots. Edge plots also showed higher β-diversity than reference plots, but only when considering dominant species. In functional terms, β-diversity among reference plots was also lower than among forest fragments and among edge plots. These patterns support the landscape-divergence hypothesis, which postulates that variable human disturbances among forest fragments and along forest edges can lead to contrasting trajectories of vegetation changes, thus increasing the compositional and functional differentiation of tree communities in these emerging environments. Our results also show that such differentiation can preserve landscape-wide biodiversity, thus overriding negative effects of habitat fragmentation on local (α) diversity. Therefore, our findings demonstrate that forest fragments and forest edges can be more valuable for maintaining species diversity and ecosystem function in fragmented tropical landscapes than previously thought.

Beetle community response to residual forest patch size in managed boreal forest landscapes: Feeding habits matter

Forest fragmentation by management activities has been implicated in the decline of forest biodiversity. Even though boreal ecosystems are generally deemed quite resilient to disturbance effects, high contemporary levels of disturbance might push forest-interior species toward decline or extinction. In this study, we examined beetle communities in forest patches of different sizes, including clearcuts, residual postharvest patches from 0.03 to 50ha in size, and large mature forest tracts (>1000ha). Overall, community structure follows a gradient between clearcuts and large mature forest tracts, even if patch size effects were more difficult to detect among patches >2.5ha. Beetles were most abundant in clearcuts, and species richness was highest in small tree groups (0.03–0.05ha). The effects of fragmentation were strongly conditioned by beetle feeding habits. Predators and xylophagous beetles were mostly associated with clearcuts or smaller patches (i.e., small tree groups or large tree groups [0.3–0.5ha]), whereas fungivorous beetles were associated with forest-interior habitats. Although many forest-interior species were still present in relatively small patches 1–5years after harvesting, negative effects of habitat fragmentation on these species might increase in the long-term.

Evaluating landscape options for corridor restoration between giant panda reserves.

The establishment of corridors can offset the negative effects of habitat fragmentation by connecting isolated habitat patches. However, the practical value of corridor planning is minimal if corridor identification is not based on reliable quantitative information about species-environment relationships. An example of this need for quantitative information is planning for giant panda conservation. Although the species has been the focus of intense conservation efforts for decades, most corridor projects remain hypothetical due to the lack of reliable quantitative researches at an appropriate spatial scale. In this paper, we evaluated a framework for giant panda forest corridor planning. We linked our field survey data with satellite imagery, and conducted species occupancy modelling to examine the habitat use of giant panda within the potential corridor area. We then conducted least-cost and circuit models to identify potential paths of dispersal across the landscape, and compared the predicted cost under current conditions and alternative conservation management options considered during corridor planning. We found that due to giant panda's association with areas of low elevation and flat terrain, human infrastructures in the same area have resulted in corridor fragmentation. We then identified areas with high potential to function as movement corridors, and our analysis of alternative conservation scenarios showed that both forest/bamboo restoration and automobile tunnel construction would significantly improve the effectiveness of corridor, while residence relocation would not significantly improve corridor effectiveness in comparison with the current condition. The framework has general value in any conservation activities that anticipate improving habitat connectivity in human modified landscapes. Specifically, our study suggested that, in this landscape, automobile tunnels are the best means to remove current barriers to giant panda movements caused by anthropogenic interferences.

Landscape corridors can increase invasion by an exotic species and reduce diversity of native species.

Landscape corridors are commonly used to mitigate negative effects of habitat fragmentation, but concerns persist that they may facilitate the spread of invasive species. In a replicated landscape experiment of open habitat, we measured effects of corridors on the invasive fire ant, Solenopsis invicta, and native ants. Fire ants have two social forms: polygyne, which tend to disperse poorly but establish at high densities, and monogyne, which disperse widely but establish at lower densities. In landscapes dominated by polygyne fire ants, fire ant abundance was higher and native ant diversity was lower in habitat patches connected by corridors than in unconnected patches. Conversely, in landscapes dominated by monogyne fire ants, connectivity had no influence on fire ant abundance and native ant diversity. Polygyne fire ants dominated recently created landscapes, suggesting that these corridor effects may be transient. Our results suggest that corridors can facilitate invasion and they highlight the importance of considering species' traits when assessing corridor utility.

Evidence for a direct negative effect of habitat fragmentation on forest herb functional diversity

The effects of habitat fragmentation on species richness and composition have been extensively studied. However, little is known about how fragmentation affects functional diversity patterns. Fragmentation can indeed affect functional diversity directly (e.g. by promoting traits associated to long-distance dispersal when fragment isolation increases) or indirectly (e.g. by decreasing species richness, hence trait diversity, when fragment area decreases). Here, we used structural equation modeling to determine whether factors associated to forest fragmentation, namely area, habitat heterogeneity, spatial isolation and age have a direct effect on forest herb functional diversity. Using occurrence data from 243 forest fragments located in northern France and six plant life-history traits, we estimated species richness and calculated functional diversity in each of these 243 forest fragments. We found that species richness was the primary driver of functional diversity in these fragments, with a strong positive and direct relationship between species richness and functional diversity. Interestingly, both fragment isolation and age had a direct negative effect on functional diversity independent of their effects on species richness. Isolation selected life-history traits associated with long-distance dispersal, while age selected for life-history traits typical of forest habitat specialists. Isolated and/or older forest fragments are thus at greater risk of local species and functional extinctions, and hence making these forest fragments particularly vulnerable to future global changes.

Strong influence of long-distance edge effect on herb-layer vegetation in forest fragments in an agricultural landscape

Abstract In agricultural landscapes in central Europe, species richness of the herbaceous plant community may be compromised by processes associated with forest fragmentation, habitat loss, and management practices. We examined variability in species richness and composition of the herbaceous layer in 229 plots located in 23 forest fragments (0.1 to 255 ha), in a representative upland agricultural landscape in central Bohemia, in relation to the most important site environmental factors, edge effects, and site history. The influence of environmental factors on the composition of vegetation in the herb layer was evaluated using generalized additive models, which enabled us to analyze highly non-linear and non-monotonic relationships. Total species richness and number of red-listed and ancient forest species were significantly influenced by type of forest vegetation, light quality, soil pH, slope aspect, and distance from the forest edge. Implications of the significant explanatory variables corresponded well to previous findings, with the exception of distance from the forest edge, for which we found a positive relationship with species richness for distances up to 200 m toward the forest interior. Plant species with low colonization ability occupied plots with increasing frequency from edge to forest interior, while fast-colonizing species showed the opposite trend. Apart from the edge effect, forest continuity should be considered for its important contribution to the richness of ancient forest and red-listed species, whereas the effect of forest fragment size appeared to be generally weak. These results do not negate the importance of large forest fragments for the maintenance of herb layer species richness, but specifically emphasize the essential contribution of the core habitats of these forests. In summary, we showed that the negative effects of habitat fragmentation on the richness of ancient forest and red-listed species and on herb layer species in total can be largely attributed to either the edge effect itself or to aggregate effects of forest edge and forest continuity.

Population dynamics of Great Bittern (Botaurus stellaris) in the Netherlands: interaction effects of winter weather and habitat fragmentation

The increased variability in weather as a manifestation of climate change is expected to have negative impacts on population survival in wildlife species, because it will likely lead to increased variation in vital demographic rates (mortality and reproduction) in these populations. For the effective protection of biodiversity, adaptation measures are needed to compensate for the expected increase in weather variability and the negative interaction with habitat fragmentation. As a case study, we studied the fluctuations in Great Bittern numbers (Botaurus stellaris) from 28 monitoring plots scattered over the Netherlands to explore the interaction between the effect of weather and possible remediating effects of the landscape structure. Great Bittern habitat surrounding these plots differs with respect to area, quality, and degree of isolation of this habitat. In western Europe, Great Bitterns are found to be susceptible to continuous loss of suitable habitat due to vegetation succession and fragmentation. Moreover, year-to-year fluctuations in local Great Bittern populations can be caused by severe winter weather or other weather extremes. Our results show that severe winter weather has indeed a significant negative impact on Great Bittern population growth rates. Furthermore, we found that an increased carrying capacity and spatial cohesion (i.e. inverse of habitat fragmentation) contribute to an increase in mean growth rates over the years. As growth rates are higher in large, well-connected habitats, we argue that recovery from negative effects of, e.g. severe winters on Great Bittern population numbers is enhanced in these less-fragmented habitats. We derived generic adaptation measures for enhancing the recovery rate of populations of species in general: one should invest in more large, well-connected nature areas, not only to diminish the negative effects of habitat fragmentation on wildlife populations, but additionally to reduce the impacts of climatic variability.