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1.
Understanding the conditions for the stable coexistence of different alleles or species is a central topic in theoretical evolution and ecology. Different causes for stable polymorphism or species coexistence have already been identified but they can be grouped into a limited number of general processes. This article is devoted to the presentation and illustration of a new process, which we call 'habitat boundary polymorphism', and which relies on two key ingredients: habitat heterogeneity and distance-limited dispersal. Under direct competition and with fixed population densities, we show that this process allows for the equilibrium coexistence of more than n types in a n-habitat environment. Distance-limited dispersal indeed creates local maladaptation at habitat edges, which leaves room for the invasion of more generalist alleles or species. This mechanism provides a generic yet neglected process for the maintenance of polymorphism or species coexistence. 相似文献
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Lenore Fahrig 《Global Ecology and Biogeography》2019,28(1):33-41
In this essay: I provide a brief history of habitat fragmentation research; I describe why its “non‐questions” (‘Is habitat fragmentation a big problem for wildlife species?” and, “Are the effects of habitat fragmentation generally negative or positive?”) are important to conservation; I outline my role in tackling these questions; I discuss reasons why the culture of habitat fragmentation research is largely incapable of accepting the answers; and I speculate on the future of habitat fragmentation research. 相似文献
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Jenni A. Stockan John Baird Simon J. Langan Mark R. Young Glenn R. Iason 《Insect Conservation and Diversity》2014,7(2):172-184
- Current restoration of stream and lotic freshwater systems to ‘good ecological status’ has focused on the creation of vegetated riparian buffer strips. Yet, despite this constituting a major land‐use change, surprisingly little is known about the effects of these strips on riparian organisms. We investigated the effect that widespread adoption of buffer strips may have on activity density, species diversity, and assemblage composition of ground beetles (Coleoptera, Carabidae).
- Over 2 years, we sampled carabids from 41 riparian margins within two river catchments in north‐east Scotland. We compared three types of riparian margin: unbuffered (i.e. ‘unimproved’), vegetated buffer strips, and wooded, the latter acting as reference sites. A range of site parameters including characteristics of soil, water, and vegetation were recorded and the extent to which they correlated with ground beetle assemblages was explored.
- Catchment and treatment effects were detected on ground beetle activity density and species diversity with unbuffered sites showing higher activity density and species richness. The assemblage structure differed according to catchment, treatment, and local characteristics. Multivariate analysis suggested that soil and vegetation parameters and stream width, together with buffer strip age and length were determinants of assemblage structure. Few riparian species were found in large numbers.
- This study shows that in intensively managed agricultural landscapes riparian buffer strips do not create the quality of habitat required by truly riparian species. They do, however, provide habitat for woodland and stenotopic species and with more careful planning could play a role in increasing habitat heterogeneity at a landscape scale.
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《Insect Conservation and Diversity》2018,11(4):396-406
- The landscape heterogeneity hypothesis posits that increasing variance of land cover types in agricultural landscapes will increase landscape level biodiversity. This hypothesis, however, does not detail which component of landscape structural heterogeneity, compositional (the type and amount) or configurational (the shape and arrangement) has the greatest influence on biodiversity and at what spatial scale(s).
- We investigated how dung beetle (Scarabaeidae) alpha‐diversity responded to landscape structural heterogeneity at a variety of spatial scales in an agricultural mosaic‐landscape in north‐eastern Swaziland. We also compared the effect of these components to the effect of variation in the amounts of major land‐cover types in the landscape and plot level vegetation structure.
- We used pitfall traps to sample the dung beetle community along a gradient of heterogeneity and used linear mixed effects models to compare the effect of each component on dung beetle richness and Shannon diversity at four separate spatial scales (i.e. 1‐,1.5‐, 2‐ & 3‐km). Land‐cover diversity and number of patches represented compositional and configurational landscape heterogeneity respectively.
- Landscape compositional heterogeneity was negatively correlated with dung beetle richness at the 1.5‐km and 2‐km spatial scales. The percentage savanna in the landscape was positively correlated with dung beetle richness at the 3‐km and 2‐km scales.
- Landscape level heterogeneity may enhance diversity of some taxonomic groups, but this was not the case for dung beetles in a southern African savanna. The best way to maintain their diversity is to create or maintain large continuous blocks of savanna while limiting intensive agriculture.
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景观空间异质性与生态系统服务的关系极为密切,适当调整景观空间异质性有助于生态系统服务的持续形成与稳定供给。研究景观空间异质性和生态系统服务形成与供给之间的相互影响作用及响应机制具有重要的理论与现实意义,是保护生物多样性、管理生态系统服务与优化景观空间配置的基础。现有研究大多在不同尺度上探讨了景观格局与生态过程或生态系统服务间的相互影响关系,而缺乏景观格局-生态过程-生态系统服务三者间有效联结等方面的研究。景观空间异质性是怎样直接或间接地作用于生态系统服务形成与供给的,目前还没有一个较为明确的解释。因此,通过分析国内外文献,回顾了景观格局或景观空间异质性与生态系统服务之间关系的研究进展、研究内容和研究方法;从景观组成、景观构型的变化入手,讨论了景观空间异质性对生态系统服务形成与供给的影响及其强度,并认为景观组成异质性变化能够直接影响生态系统服务,而景观构型异质性变化会通过改变生态过程而间接影响生态系统服务;阐述了景观空间异质性在影响生态系统服务形成与供给的同时,也使生态系统服务在空间上产生了异质性分布,并从自然因素和人为因素两个方面对其进行解释;强调了尺度问题在景观空间异质性与生态系统服务研究中的重要性;最后,明确了对生态系统服务形成与供给的景观空间异质性影响研究不仅有助于生态系统服务的维持与调节,也能更深层次地揭示其中的生态学意义。 相似文献
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Carmen Galn‐Acedo Víctor Arroyo‐Rodríguez Sabine J. Cudney‐Valenzuela Lenore Fahrig 《Biological reviews of the Cambridge Philosophical Society》2019,94(5):1605-1618
Land‐use change modifies the spatial structure of terrestrial landscapes, potentially shaping the distribution, abundance and diversity of remaining species assemblages. Non‐human primates can be particularly vulnerable to landscape disturbances, but our understanding of this topic is far from complete. Here we reviewed all available studies on primates' responses to landscape structure. We found 34 studies of 71 primate species (24 genera and 10 families) that used a landscape approach. Most studies (82%) were from Neotropical forests, with howler monkeys being the most frequently studied taxon (56% of studies). All studies but one used a site‐landscape or a patch‐landscape study design, and frequently (34% of studies) measured landscape variables within a given radius from the edge of focal patches. Altogether, the 34 studies reported 188 responses to 17 landscape‐scale metrics. However, the majority of the studies (62%) quantified landscape predictors within a single spatial scale, potentially missing significant primate–landscape responses. To assess such responses accurately, landscape metrics need to be measured at the optimal scale, i.e. the spatial extent at which the primate–landscape relationship is strongest (so‐called ‘scale of effect’). Only 21% of studies calculated the scale of effect through multiscale approaches. Interestingly, the vast majority of studies that do not assess the scale of effect mainly reported null effects of landscape structure on primates, while most of the studies based on optimal scales found significant responses. These significant responses were primarily to landscape composition variables rather than landscape configuration variables. In particular, primates generally show positive responses to increasing forest cover, landscape quality indices and matrix permeability. By contrast, primates show weak responses to landscape configuration. In addition, half of the studies showing significant responses to landscape configuration metrics did not control for the effect of forest cover. As configuration metrics are often correlated with forest cover, this means that documented configuration effects may simply be driven by landscape‐scale forest loss. Our findings suggest that forest loss (not fragmentation) is a major threat to primates, and thus, preventing deforestation (e.g. through creation of reserves) and increasing forest cover through restoration is critically needed to mitigate the impact of land‐use change on our closest relatives. Increasing matrix functionality can also be critical, for instance by promoting anthropogenic land covers that are similar to primates' habitat. 相似文献
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J. Tews U. Brose V. Grimm K. Tielbörger M. C. Wichmann M. Schwager F. Jeltsch 《Journal of Biogeography》2004,31(1):79-92
Aim In a selected literature survey we reviewed studies on the habitat heterogeneity–animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support. Location World-wide. Methods We reviewed 85 publications for the period 1960–2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study. Main conclusions The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper, we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across-studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to ‘keystone structures’ that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management. 相似文献
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Abstract. Small‐scale landscape elements, such as ditch banks, play an important role in preserving plant species richness in agricultural landscapes. In this study, we investigate whether the seed bank might be useful for restoring the above‐ground plant species richness. We studied the vegetation and seed bank composition at six species‐rich and six species‐poor ditch banks, where agri‐environment schemes are running to maintain and enhance ditch bank plant diversity. We show that the number of species in the seed bank was low, regardless of the number of species in the established vegetation. Moreover, the seed bank was always dissimilar to the established vegetation. Target species for nature conservation were occasionally present in the seed bank at both species‐poor and species‐rich sites, but rarely so if the species was absent from the established vegetation. We conclude that the potential use of the seed bank for restoration of ditch banks is minimal. At present, plant species richness seems to be largely controlled by germination opportunities; high biomass and competition appear to hamper germination at species‐poor sites. We recommend continued nutrient reduction at such sites. Soil disturbance measures and deliberate sowing should also be considered. 相似文献
9.
Santiago Saura 《Journal of Biogeography》2021,48(1):11-22
The 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. 相似文献
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Numerous metrics describing landscape patterns have been used to explain landscape-scale habitat selection by birds. The myriad metrics, their complexity, and inconsistent responses to them by birds have led to a lack of clear recommendations for managing land for desired species. The amount of a target land cover type in the landscape (percentage cover) often has been a useful indicator of the likelihood of species occurrence or of habitat selection; is it also a more adequate and parsimonious measure for explaining species distributions than patch size or more complex measures of landscape configuration? We examined responses of 6 woodland-interior bird species to the percentage tree cover within prescribed areas and to patch size, edge density, and other metrics. We examined responses in 2 landscapes: a mixed woodland-savanna and an eastern deciduous forest. For these 6 species, percentage tree cover explained bird occurrence as well as or better than other measures in both study areas. We then repeated the analysis on a larger group of woodland species, including those associated with woodland edges. The bird species we studied had varied responses to landscape metrics, but percentage tree cover was the strongest explanatory variable overall. Although percentage cover estimated from remotely sensed data is an inexact representation of habitat in the landscape, it does appear to be reliable and easy to conceptualize, relative to other measures. We suggest that, at least for woodland habitat, percentage cover is a broadly useful measure that can be helpful in pragmatic questions of explaining responses to landscapes or in anticipating responses to landscape change. © 2011 The Wildlife Society. 相似文献
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Daire
hUallachin Annette Anderson Rochelle Fritch Stephen McCormack Helen Sheridan John A. Finn 《Insect Conservation and Diversity》2014,7(4):289-307
- Field margins within intensively managed ecosystems are often seen as a last refuge for biodiversity, and are typically targeted with measures within many agri‐environment schemes. Grassland accounts for 81 million ha of land within the EU; however, the ecology of field margins associated with permanent grassland has not been well studied.
- This study investigated the effects of experimental field margin measures on hymenopteran parasitoid communities over a 5‐year period. Hymenopteran parasitoids were chosen because they occupy high trophic levels, feed on a diverse range of plant and invertebrate hosts, and are considered good indicators of arthropod diversity. Establishment methods included: fencing, natural regeneration, and reseeding with a wildflower mixture, at three margin widths.
- Field margin establishment method had a significant effect on abundance of parasitoids. Establishment method did not have a significant effect on parasitoid genera diversity, but did affect parasitoid community composition. Margin width had no significant impact on parasitoid communities.
- Grazing had a significant negative effect on parasitoid genus richness and community structure. This suggests that structural diversity of vegetation plays an important role in parasitoid community structure.
- Plant species richness did not significantly affect parasitoid abundance or genera richness. Noxious species within plots resulted in a significantly greater abundance and diversity of parasitoids and of idiobionts in particular.
- Where plant species richness is limited, simple measures such as fencing of narrow field margins may be as effective at increasing parasitoid taxon richness and abundance (indicators of arthropod richness and abundance) as expensive measures such as reseeding and wider margin widths.
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Amaranta Arellano-Rivas J. Arturo De-Nova Miguel A. Munguí a-Rosas 《Journal of Plant Ecology》2018,11(1):136
Aims It is known that taxonomic diversity can be predicted by the spatial configuration of the habitat, in particular by its area and degree of isolation. However, taxonomic diversity is a poor predictor of ecosystem functioning. While functional diversity is strongly linked to the functionality and stability of ecosystems, little is known about how changes in the spatial configuration of the habitat affect functional diversity. In this study, we evaluated whether the spatial configuration of forest patches predicts the functional diversity of plants in a fragmented forest.Methods Five functional leaf traits (leaf dry matter content, leaf punch force, specific leaf area, leaf size and leaf thickness) were measured for 23 dominant plant species in 20 forest patches in a naturally fragmented forest on the Yucatan Peninsula. Abundance-weighted multivariate and individual trait metrics of functional diversity were calculated and correlated with size, degree of isolation and the shape of forest patches.Important findings Patch shape was negatively correlated with multivariate and individual trait (leaf dry matter content and leaf size) metrics of functional diversity. Patch isolation measures were also negatively correlated with individual trait (leaf dry matter content, leaf punch force and leaf size) metrics of functional diversity. In other words, greater patch shape irregularity and isolation degree impoverish plant functional variability. This is the first report of the negative effects of patch shape irregularity and isolation on the functional diversity of plant communities in a forest that has been fragmented for a long time. 相似文献
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Habitat fragmentation and loss affect population stability and demographic processes, increasing the extinction risk of species. We studied Anolis heterodermus populations inhabiting large and small Andean scrubland patches in three fragmented landscapes in the Sabana de Bogotá (Colombia) to determine the effect of habitat fragmentation and loss on population dynamics. We used the capture‐mark‐recapture method and multistate models to estimate vital rates for each population. We estimated growth population rate and the most important processes that affect λ by elasticity analysis of vital rates. We tested the effects of habitat fragmentation and loss on vital rates of lizard populations. All six isolated populations showed a positive or an equilibrium growth rate (λ = 1), and the most important demographic process affecting λ was the growth to first reproduction. Populations from landscapes with less scrubland natural cover showed higher stasis of young adults. Populations in highly fragmented landscapes showed highest juvenile survival and growth population rates. Independent of the landscape's habitat configuration and connectivity, populations from larger scrubland patches showed low adult survivorship, but high transition rates. Populations varied from a slow strategy with low growth and delayed maturation in smaller patches to a fast strategy with high growth and early maturation in large patches. This variation was congruent with the fast‐slow continuum hypothesis and has serious implications for Andean lizard conservation and management strategies. We suggest that more stable lizard populations will be maintained if different management strategies are adopted according to patch area and habitat structure. 相似文献
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- Hoverflies provide ecosystem services including pollination, pest regulation and waste decomposition, but not enough is known about how they are influenced by organic farming and landscape composition, and structure to effectively manage them in different landscapes.
- By conducting transect walks and pan‐trapping, we investigated how hoverfly abundance/richness were related to organic farming, floral abundance, land‐use cover and hedgerows in nine pairs of organic and conventional dairy farms in the Republic of Ireland.
- We found more flowers on organic farms which attracted more hoverfly species. Organic farming also increased hoverfly abundance and richness beyond the benefits from increased floral resources, indicating that other organic management practices benefit hoverflies. This was evident regardless of the surrounding landscape composition.
- Hoverfly abundance and richness were most strongly related to land use within 4 km around sites, indicating the importance of large spatial scales. Homogenous grassland landscapes (i.e. high grassland cover) supported higher hoverfly abundance and richness, possibly because they contain abundant macrohabitats suitable for the proliferation of grassland hoverflies. Hedgerow structure was also important, with hoverfly abundances greater on sites surrounded by a higher total cover of hedgerows, but with lower total hedgerow lengths (i.e. greater hedgerow volumes) within 1 km.
- Our findings illustrate complex relationships between hoverflies and local and landscape factors, and they contrast with previous findings for other pollinators. We encourage increased floral resources and organic farming as a means of conserving hoverflies in grassland systems. Future management of grassland hoverflies needs to account for large spatial scales and the possibility that hedgerows greatly impact hoverfly diversity in hedgerow‐dominated landscapes.
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- It is not known if grassy margins contribute to the conservation of biodiversity if situated along organically managed cereal fields as the contrast in environmental conditions between fields and margins may be too small in absence of pesticide applications.
- Communities of spiders, ground beetles, true bugs and aphids were sampled in 2 years along transects from the centre of organically managed cereal fields into adjacent grassy margins. Based on species richness, abundances, ecological and body size traits of species and taxonomic distinctness between species, communities were compared between organically managed cereal fields and their grassy margins.
- The species richness, abundance and variation in taxonomic distinctness of true bugs were significantly higher in grassy margins. For spiders and ground beetles, these metrics were either higher in cereal fields or did not differ significantly. At the species level, spiders living under stones or in soil crevices, as well as phytophagous ground beetles and true bugs that overwinter as eggs benefited from grassy margins. True bug communities in cereal fields were dominated by a few abundant species, whereas communities in margins were rather dominated by a few large species.
- Our comprehensive analyses highlight the importance of accounting for species identities and biology in biodiversity studies. The traits that characterised arthropod species that benefited from margins are not characteristic for pest species. Grassy margins along organic fields therefore represent an important agri‐environmental scheme for the conservation of several arthropod taxa and margins should not be removed to increase the crop production area in organically managed cereal fields.
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Christina M. Kennedy Eric Lonsdorf Maile C. Neel Neal M. Williams Taylor H. Ricketts Rachael Winfree Riccardo Bommarco Claire Brittain Alana L. Burley Daniel Cariveau Luísa G. Carvalheiro Natacha P. Chacoff Saul A. Cunningham Bryan N. Danforth Jan‐Hendrik Dudenhffer Elizabeth Elle Hannah R. Gaines Lucas A. Garibaldi Claudio Gratton Andrea Holzschuh Rufus Isaacs Steven K. Javorek Shalene Jha Alexandra M. Klein Kristin Krewenka Yael Mandelik Margaret M. Mayfield Lora Morandin Lisa A. Neame Mark Otieno Mia Park Simon G. Potts Maj Rundlf Agustin Saez Ingolf Steffan‐Dewenter Hisatomo Taki Blandina Felipe Viana Catrin Westphal Julianna K. Wilson Sarah S. Greenleaf Claire Kremen 《Ecology letters》2013,16(5):584-599
Bees provide essential pollination services that are potentially affected both by local farm management and the surrounding landscape. To better understand these different factors, we modelled the relative effects of landscape composition (nesting and floral resources within foraging distances), landscape configuration (patch shape, interpatch connectivity and habitat aggregation) and farm management (organic vs. conventional and local‐scale field diversity), and their interactions, on wild bee abundance and richness for 39 crop systems globally. Bee abundance and richness were higher in diversified and organic fields and in landscapes comprising more high‐quality habitats; bee richness on conventional fields with low diversity benefited most from high‐quality surrounding land cover. Landscape configuration effects were weak. Bee responses varied slightly by biome. Our synthesis reveals that pollinator persistence will depend on both the maintenance of high‐quality habitats around farms and on local management practices that may offset impacts of intensive monoculture agriculture. 相似文献