Effect of forest fragmentation on the woody flora of the highlands of Chiapas, Mexico

This study was conducted in the Chiapas Highlands, a tropical mountain region where traditional agricultural practices have resulted in a mosaic landscape of forest fragments embedded in a matrix of secondary vegetation and crop fields. The question addressed was how may woody species richness be affected by forest fragment attributes derived from traditional land-use patterns. Species inventories of total woody species, canopy and understorey trees, and shrubs were obtained in 22 forest fragments (5 ha). Multiple regression analyses were applied to examine the effects of size, matrix, isolation and shape of the forest fragments on richness of these species guilds. Fragment size was correlated with shape (r = 0.75) and isolation (r = –0.69), and isolation was correlated with shape (r = –0.75). Total species richness, and number of shrubs and understorey trees in fragments were related to isolation; moreover, additive effects of fragment shape were found for shrubs. The number of canopy species was not related to any fragment variable. Matrix did not help to explain species richness, possibly due to the landscape structure created by the traditional land-use patterns. In addition to size and isolation, we point out the need of considering shape and matrix as additional fragmentation attributes, along with social and economic factors, if we are ever going to be successful in our management and conservation actions.     

Integrating edge effects into studies of habitat fragmentation: a test using meiofauna in seagrass

Habitat fragmentation is thought to be an important process structuring landscapes in marine and estuarine environments, but effects on fauna are poorly understood, in part because of a focus on patchiness rather than fragmentation. Furthermore, despite concomitant increases in perimeter:area ratios with fragmentation, we have little understanding of how fauna change from patch edges to interiors during fragmentation. Densities of meiofauna were measured at different distances across the edges of four artificial seagrass treatments [continuous, fragmented, procedural control (to control for disturbance by fragmenting then restoring experimental plots), and patchy] 1 day, 1 week and 1 month after fragmentation. Experimental plots were established 1 week prior to fragmentation/disturbance. Samples were numerically dominated by harpacticoid copepods, densities of which were greater at the edge than 0.5 m into patches for continuous, procedural control and patchy treatments; densities were similar between the edge and 0.5 m in fragmented patches. For taxa that demonstrated edge effects, densities exhibited log-linear declines to 0.5 m into a patch with no differences observed between 0.5 m and 1 m into continuous treatments. In patchy treatments densities were similar at the internal and external edges for many taxa. The strong positive edge effect (higher densities at edge than interior) for taxa such as harpacticoid copepods implies some benefit of patchy landscapes. But the lack of edge effects during patch fragmentation itself demonstrates the importance of the mechanisms by which habitats become patchy.     

Dynamics of neutral biodiversity

Hubbell's neutral model has become a major paradigm in ecology. Whereas the steady-state structure is well understood, results about the dynamical aspects of the model are scarce. Here we derive dynamical equations for the Simpson diversity index. Both mean and variance of the diversity are proven to satisfy stable linear system dynamics. We show that in the stationary limit we indeed recover previous results, and we supplement this with numerical simulations to validate the dynamical part of our analytical computations. These findings are especially relevant for experiments in microbial ecology, where the Simpson diversity index can be accurately measured as a function of time.     

Species richness and composition of amphibians and reptiles in a fragmented forest landscape in northeastern Bolivia

We quantified patterns of species richness and species composition of frogs and reptiles (lizards and snakes) among three habitats (continuous forest, forest islands, and a seasonally flooded savannah) and between forest island size and isolation classes in a floristic transition zone in northeastern Santa Cruz Department, Bolivia. Species richness was similar across macrohabitats, as was faunal composition of forested habitats, although savannah harbored a distinct herpetofauna. On forest islands, richness and composition of forest frogs was largely related to isolation, whereas reptiles were affected by both isolation and habitat. The observation that isolation rather than area was the primary driver of distribution patterns on forest islands stands in contrast to many studies, and may be a function of (1) the greater range in forest island isolation values compared to area or (2) the long history of isolation in this landscape.     

Extinction debt of cities and ways to minimise their realisation: a focus on Melbourne

The formation and growth of cities sets in train a slow process of local species extinction, although it can take a long time for that extinction to be realised. Using Melbourne as an example, the authors ask ‘What plant species are potentially at risk and what strategies and actions could minimise the predicted negative outcomes?’     

Tools and techniques for investigating impacts of habitat complexity on biological control

Across the globe, landscapes are becoming altered as natural habitats are converted to agriculture or development. Consequently, a critical question is how changes in habitat complexity and composition might influence ecosystem services such as biological control. Although the development of new statistical, molecular, and digital technologies offers exciting opportunities to explore this issue, the appropriate usage of these tools is crucial to any successful study. This review examines the tools and techniques employed to investigate relationships between habitat complexity and biological control, and their appropriateness in different contexts. We examine various definitions of the explanatory variable, habitat complexity, and methods to experimentally measure the response variable, biological control. We conclude with a summary of the different statistical techniques available to assess linkages between habitat complexity and biological control. This review will facilitate future research on habitat complexity and biological control and will thus aid in the conservation of this valuable ecosystem service.     

Neutral models and the deviation from neutral pattern metric

Ecological variables are inherently spatial with arrangement on the landscape often directly attributed to underlying processes. Historically, assumptions regarding the relationships among scale, pattern, and process have been used to characterize landscapes as well as compare multiple landscapes or changes in landscapes over time. Despite the utility of landscape comparisons, they often fail to adequately link scale, pattern, or process, and far too frequently are presented as logical interpretations leading to prediction of pattern to process relationships. Pattern metrics and measures of spatial autocorrelation have evolved to characterize and model landscape phenomena. Unfortunately, the two are quite often misapplied. This research presents an alternative metric, Deviation from Neutral (DFN), which permits the comparison of multiple landscapes.     

Speciation and the neutral theory of biodiversity

The neutral theory of biodiversity purports that patterns in the distribution and abundance of species do not depend on adaptive differences between species (i.e. niche differentiation) but solely on random fluctuations in population size (“ecological drift”), along with dispersal and speciation. In this framework, the ultimate driver of biodiversity is speciation. However, the original neutral theory made strongly simplifying assumptions about the mechanisms of speciation, which has led to some clearly unrealistic predictions. In response, several recent studies have combined neutral community models with more elaborate speciation models. These efforts have alleviated some of the problems of the earlier approaches, while confirming the general ability of neutral theory to predict empirical patterns of biodiversity. However, the models also show that the mode of speciation can have a strong impact on relative species abundances. Future work should compare these results to diversity patterns arising from non‐neutral modes of speciation, such as adaptive radiations.     

Large-scale forest fragmentation increases the duration of tent caterpillar outbreak

I examined historical data (1950–1984) on the duration of outbreaks of the forest tent caterpillar (Malacosoma disstria) in northern Ontario, Canada. Outbreak duration was compared to host tree species dominance and forest structure over large areas of boreal forest partially cleared for agriculture. Abundance of the principal host tree species Populus tremuloides had no consistent effect on duration of outbreak within forest districts, and was negatively correlated with duration of outbreaks among the eight forest districts examined. The amount of forest edge per km² was the best, and most consistent, predictor of the duration of tent caterpillar outbreaks both within individual forest districts and among forest districts. Because forest tent caterpillar populations are driven largely by the impact of parasitoids and pathogens, results here suggest that large-scale increase in forest fragmentation affects the interaction between these natural enemies and forest tent caterpillar. Increased clearing and fragmentation of boreal forests, by agriculture and forestry, may be exacerbating outbreaks of this forest defoliator.     

Slight differences among individuals and the unified neutral theory of biodiversity

The unified neutral theory of biodiversity provides a very simple and counterintuitive explanation of species diversity patterns. By specifying speciation, community size and dispersal, and completely ignoring differences among individual organisms and species, it generates biodiversity patterns that remarkably resemble natural ones. Here I show that adding even slight differences among organisms generates very different patterns and predictions. In large communities with widespread dispersal, heritable differences in viability among individual organisms lead to biodiversity patterns characterised by the overdominance of a single species comprising organisms with relatively high fitness. In communities with local dispersal, the same differences produce rapid community extinction. I conclude that the unified neutral theory is not robust to slight deviations from its most controversial assumption.     

Tolerance to habitat fragmentation influences the colonization of new habitat by forest birds

We examined the relationship between the ability of bird species to persist in fragmented forests and their ability to colonize new forest habitat. Using a long-term data set on the colonization of a forest plantation, we tested the hypothesis that bird species tolerant to habitat fragmentation would detect and colonize the new habitat faster than intolerant species. The forest plantation under study is situated on an area of land reclaimed from the sea (a polder) in the central part of The Netherlands. We constructed an index of tolerance to habitat fragmentation and included it as a predictor variable in a set of three logistic regression models that compared the probability of colonization over four consecutive time periods. After controlling statistically for the effects of regional incidence, preferred habitat and life-history characteristics, there was a significant effect of tolerance to fragmentation on the ability of species to colonize the plantation, and a marginal effect on the timing of colonization. We then examined the effect of the same index of tolerance to fragmentation on colonization patterns over a larger spatial scale. Multivariate regression models showed that the proportion of three polders of different ages occupied by forest bird species was dependent upon the regional incidence of a species, its preferred habitat and its tolerance to fragmentation. The results support the hypothesis that species tolerant to habitat fragmentation detect and colonize new habitat faster than those intolerant to habitat fragmentation.     

生境破碎化对生物多样性的影响

生境破碎化对生物多样性和生态系统功能的影响是当前国内外生态学家研究的热点问题之一。生境破碎化导致原生境的总面积减小,产生隔离的异质种群,从而影响个体行为特性、种群间基因交换、物种间相互作用及生态过程。生境破碎化的过程引起栖息地内部食物、繁殖场所、局部小气候、边缘效应等生物和非生物条件的变化,从而影响植物种群的大小和灭绝速率、扩散和迁入、遗传和变异以及存活力等,影响动物种群的异质种群动态、适宜生境比例、灭绝阈值、种间关系等。随着景观生态学与农业科学的融合,探索利用景观布局控制害虫发生将是人类利用生境破碎化为人类服务的一条新途径。     

Landscape dynamics and their effect on the functional connectivity of a Mediterranean landscape in Chile

Land use and cover changes have been identified as a major factor contributing to shape landscape structure and biodiversity patterns, particulary in areas with a long history of human occupation and habitat fragmentation, such as the Mediterranean landscapes. However, the existing studies on landscape change indicators for Mediterranean areas have mostly focused in Europe, while for other Mediterranean zones, and especially for South America, there is a serious lack of knowledge concerning the impact of landscape dynamics on ecological processes. Further research on this topic is urgently needed, given the high biodiversity levels and the rapidly increasing rates of human modification in the Mediterranean landscapes of South America. For this purpose, we investigated the dynamics of a landscape in the semiarid region of the Mediterranean zone of Chile, and measured the effect of those dynamics on functional connectivity, during a period of about four decades (1975–2011). Landscape connectivity indicators were extracted from a series of Landsat images. The Equivalent Connnected Area index (ECA) was used as indicator of connectivity trends, and was evaluated for three representative distances of seed dispersal in the study area (150 m, 500 m and 1000 m). In addition, the patches that most contribute to maintain the present connectivity, and their roles as connectivity providers, were identified through a set of commensurable indicators: betweenness centrality and the fractions (intra, flux connector) of the Integral Index of Connectivity. We found that these indicators were useful to detect and summarize a number of previously unreported trends in these Mediterranean landscapes. First, population growth and economic development were compatible with an increase in functional connectivity for forest habitats, mainly because the abandonment of marginal agricultural lands and their subsequent conversion to espinals (Acacia caven) triggered vegetation succession towards secondary forests. Second, increased forest connectivity was not associated to a decrease in the characteristic heterogeneity of Mediterranean landscapes. Third, many patches of espinal, despite being commonly regarded as of poor conservation value, were crucial to promote connectivity by acting as stepping stones among other patches with higher habitat quality. The approach here presented provides a combined assessment of landscape structure, function and change that should be valuable and applicable to deliver operational indicators in dynamic landscapes in South America and other Mediterranean regions.     

Functional trait variation of forest understorey plant communities across Europe

Global environmental changes are expected to alter the functional characteristics of understorey herb-layer communities, potentially affecting forest ecosystem functioning. However, little is known about what drives the variability of functional traits in forest understories. Here, we assessed the role of different environmental drivers in shaping the functional trait distribution of understorey herbs in fragmented forests across three spatial scales. We focused on 708 small, deciduous forest patches located in 16 agricultural landscape windows, spanning a 2500-km macroclimatic gradient across the temperate forest biome in Europe. We estimated the relative effect of patch-scale, landscape-scale and macroclimatic variables on the community mean and variation of plant height, specific leaf area and seed mass. Macroclimatic variables (monthly temperature and precipitation extremes) explained the largest proportion of variation in community trait means (on average 77% of the explained variation). In contrast, patch-scale factors dominated in explaining community trait variation (on average 68% of the explained variation). Notably, patch age, size and internal heterogeneity had a positive effect on the community-level variability. Landscape-scale variables explained only a minor part of the variation in both trait distribution properties. The variation explained by shared combinations of the variable groups was generally negligible. These findings highlight the importance of considering multiple spatial scales in predictions of environmental-change effects on the functionality of forest understories. We propose that forest management sustainability could benefit from conserving larger, historically continuous and internally heterogeneous forest patches to maximise ecosystem service diversity in rural landscapes.     

Time-dependent solutions of the spatially implicit neutral model of biodiversity

Previous research into the neutral theory of biodiversity has focused mainly on equilibrium solutions rather than time-dependent solutions. Understanding the time-dependent solutions is essential for applying neutral theory to ecosystems in which time-dependent processes, such as succession and invasion, are driving the dynamics. Time-dependent solutions also facilitate tests against data that are stronger than those based on static equilibrium patterns. Here I investigate the time-dependent solutions of the classic spatially implicit neutral model, in which a small local community is coupled to a much larger metacommunity through immigration. I present explicit general formulas for the eigenvalues, left eigenvectors and right eigenvectors of the models’s transition matrix. The time-dependent solutions can then be expressed in terms of these eigenvalues and eigenvectors. Some of these results are translated directly from existing results for the classic Moran model of population genetics (the Moran model is equivalent to the spatially implicit neutral model after a reparameterization); others of the results are new. I demonstrate that the asymptotic time-dependent solution corresponding to just these first two eigenvectors can be a good approximation to the full time-dependent solution. I also demonstrate the feasibility of a partial eigendecomposition of the transition matrix, which facilitates direct application of the results to a biologically relevant example in which a newly invading species is initially present in the metacommunity but absent from the local community.     

景观健康概念、特征及其评价

景观健康是近年来出现景观生态学与新兴的生态系统健康学领域的一个新的生态学概念,旨在探讨人类强烈活动干扰下遭受严重污染与退化,甚至会逐渐消失的景观生态系统的健康问题。本文针对目前所存在的有关景观健康的基本概念,景观健康的特征与标准进行了详细介绍,并就景观健康评价指标的确立,评价时空尺度与等级以及评价方法分别进行了探讨。最后,还强调了在进行景观健康评价时应运用比较的,综合的以及发展的观点开展研究。     

Extinction rate, historical population structure and ecological role of the Caribbean monk seal

The productivity and biomass of pristine coral reef ecosystems is poorly understood, particularly in the Caribbean where communities have been impacted by overfishing and multiple other stressors over centuries. Using historical data on the spatial distribution and abundance of the extinct Caribbean monk seal (Monachus tropicalis), this study reconstructs the population size, structure and ecological role of this once common predator within coral reef communities, and provides evidence that historical reefs supported biomasses of fishes and invertebrates up to six times greater than those found on typical modern Caribbean reefs. An estimated 233,000-338,000 monk seals were distributed among 13 colonies across the Caribbean. The biomass of reef fishes and invertebrates required to support historical seal populations was 732-1018 gm(-2) of reefs, which exceeds that found on any Caribbean reef today and is comparable with those measured in remote Pacific reefs. Quantitative estimates of historically dense monk seal colonies and their consumption rates on pristine reefs provide concrete data on the magnitude of decline in animal biomass on Caribbean coral reefs. Realistic reconstruction of these past ecosystems is critical to understanding the profound and long-lasting effect of human hunting on the functioning of coral reef ecosystems.     

Controlled experiments of habitat fragmentation: a simple computer simulation and a test using small mammals

Habitat fragmentation involves a reduction in the effective area available to a population and the imposition of hard patch edges. Studies seeking to measure effects of habitat fragmentation have compared populations in fragments of different size to estimate and area effect but few have examined the effect of converting open populations to closed ones (an effect of edges). To do so requires a shift in spatial scope-from comparison of individual fragments to that of fragmented versus unfragmented landscapes. Here we note that large-scale, controlled studies of habitat fragmentation have rarely been performed and are needed. In making our case we develop a simple computer simulation model based on how individual animals with home ranges are affected by the imposition of habitat edges, and use it to predict population-level responses to habitat fragmentation. We then compare predictions of the model with results from a field experiment on Peromyscus and Microtus. Our model treats the case where home ranges/territories fall entirely within or partially overlap with that of sample areas in continuous landscapes, but are restricted to areas within habitat fragments in impacted landscapes. Results of the simulations demonstrate that the imposition of hard edges can produce different population abundances for similar-sized areas in continuous and fragmented landscapes. This edge effect is disproportionately greater in small than large fragments and for species with larger than smaller home ranges. These predictions were generally supported by our field experiment. We argue that large-scale studies of habitat fragmentation are sorely needed, and that control-experiment contrasts of fragmented and unfragmented microlandscapes provide a logical starting point.