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1.
Accurate evaluation of habitat availability for wildlife is relevant for ecological applications. Researchers have frequently used models to simulate habitats thermally suitable for reptiles, but these results have limited application for species highly selective for habitat humidity. Here, we use the biophysical Niche Mapper™ model to investigate impacts of vegetation cover on the habitat quality of a high-elevation forest skink, Sphenomorphus taiwanensis, and to predict changes in habitat suitability in a future warmer climate (3 °C increase in air temperature). We assess habitat suitability with different densities of canopy cover in our study areas using two ecologically relevant estimates for lizards: maximum activity time and evaporative water loss (EWL) during the activity season. We measured preferred body temperature and EWL of this species for model parameterization, and behavioral response to EWL to supplement habitat quality assessment. The results indicated that this species is sensitive to EWL and reduces its activity when dehydrated. The model predicted that denser canopy levels increase microclimate cooling and humidity, and that most canopy levels are thermally suitable for this species, as the lizard can thermoregulate to manage adverse temperatures. Nevertheless, increasing canopy density could significantly decrease EWL during activity. In the warmer climate scenario, simulated maximum activity time and EWL changed little because of thermoregulation behavior. Our results suggest that habitat preference of this species is a consequence of water and energy requirements, and we note that combining EWL and maximum activity time data can enhance model accuracy of lizards’ habitat quality in a warmer climate.  相似文献   

2.
Fire can influence the microclimate of forest habitats by removing understory vegetation and surface debris. Temperature is often higher in recently burned forests owing to increased light penetration through the open understory. Because physiological processes are sensitive to temperature in ectotherms, we expected fire-maintained forests to improve the suitability of the thermal environment for turtles, and for turtles to seasonally associate with the most thermally-optimal habitats. Using a laboratory thermal gradient, we determined the thermal preference range (Tset) of eastern box turtles, Terrapene carolina, to be 27–31 °C. Physical models simulating the body temperatures experienced by turtles in the field revealed that surface environments in a fire-maintained longleaf pine forest were 3 °C warmer than adjacent unburned mixed hardwood/pine forests, but the fire-maintained forest was never of superior thermal quality owing to wider Te fluctuations above Tset and exposure to extreme and potentially lethal temperatures. Radiotracked turtles using fire-managed longleaf pine forests maintained shell temperatures (Ts) approximately 2 °C above those at a nearby unburned forest, but we observed only moderate seasonal changes in habitat use which were inconsistent with thermoregulatory behavior. We conclude that turtles were not responding strongly to the thermal heterogeneity generated by fire in our system, and that other aspects of the environment are likely more important in shaping habitat associations.  相似文献   

3.
A widely accepted biodiversity crisis in the tropics has been recently challenged by claims that secondary forests will gradually restore biodiversity losses. This prediction was examined for the herpetofauna in Quintana Roo, Mexico. Quantitative sampling (108 transects) of reptiles was undertaken monthly (January–September 2004) along a vegetation gradient covering induced grasslands, and regrowth and primary rain forests. A total of 35 species was found, 14 being present in and five showing dependence on mature forests. Lizards contributed > 90 per cent of the individuals observed. Reptile abundance and snake species richness was highest in primary forests, even though the lower abundance and richness did not differ between regrowth forest and induced grasslands. Multivariate ordinations and ANOSIM tests displayed clear differences in assemblage structure among vegetation types, mainly caused by contrasting abundances of lizard species having distinctive arboreal or terrestrial habits. There was no evidence that snake assemblages differed between secondary forests and induced grasslands. Microhabitat availability had a key role in shaping species composition through the vegetation gradient. Our results dismiss the hypothesis that secondary forests can act as reservoirs of primary forest reptile diversity on the basis that many taxa depend largely on habitat quality and have specialized life‐history traits, and that biological succession does not guarantee the recovery of assemblage complexity.  相似文献   

4.
Understanding the interacting role of climate and habitat in shaping wildlife population dynamics can help to reveal synergistic pathways that drive population resilience or decline across variable and changing environments. Moose (Alces alces) is a pan-boreal herbivore experiencing population declines across large portions of North America; however, the species has shown variable response to climate across its distribution. We investigated moose demographic response to climate and evaluated the interacting role of habitat across 36 years and along a biogeographic gradient in Ontario, Canada that has experienced decadal changes to climate and habitat quality. Moose density exhibited a nonlinear trend that initially increased and then decreased over the study timeframe and was negatively affected by regional and local patterns of winter severity and later frost onset. Recruitment exhibited a monotonic decline and was positively affected by spring heat and deciduous forest cover, while also exhibiting density-dependent effects. The negative response of moose density to winter severity was reduced in Wildlife Management Units (WMUs) with higher proportions of dense canopy cover, supporting expectations that this habitat type improves moose winter mobility and predator avoidance. The negative effect of later frost onset was greater in WMUs with more regenerating forest, and both variables are associated with higher exposure to parasites and predators. Further, density-dependent effects on recruitment were suppressed by warmer springs that support vegetation productivity and in WMUs with higher proportions of dense canopy cover that can provide concealment from predators. Our study illustrates the important role habitat conditions can have to mitigate, or exacerbate, climate-change effects for a wide-spread herbivore occupying variable environments by potentially altering pathways relevant to energetic balance, predation, and parasite transmission. In this system, moose occupying sparse or regenerating forests are more susceptible to adverse climatic effects and should be managed accordingly.  相似文献   

5.
Changes to vegetation structure and composition in forests adapted to frequent fire have been well documented. However, little is known about changes to the spatial characteristics of vegetation in these forests. Specifically, patch sizes and detailed information linking vegetation type to specific locations and growing conditions on the landscape are lacking. We used historical and recent aerial imagery to characterize historical vegetation patterns and assess contemporary change from those patterns. We created an orthorectified mosaic of aerial photographs from 1941 covering approximately 100,000 ha in the northern Sierra Nevada. The historical imagery, along with contemporary aerial imagery from 2005, was segmented into homogenous vegetation patches and classified into four relative cover classes using random forests analysis. A generalized linear mixed model was used to compare topographic associations of dense forest cover on the historical and contemporary landscapes. The amount of dense forest cover increased from 30 to 43% from 1941 to 2005, replacing moderate forest cover as the most dominant class. Concurrent with the increase in extent, the area-weighted mean patch size of dense forest cover increased tenfold, indicating greater continuity of dense forest cover and more homogenous vegetation patterns across the contemporary landscape. Historically, dense forest cover was rare on southwesterly aspects, but in the contemporary forest, it was common across a broad range of aspects. Despite the challenges of processing historical air photographs, the unique information they provide on landscape vegetation patterns makes them a valuable source of reference information for forests impacted by past management practices.  相似文献   

6.
Transportation infrastructure is a main cause of environmental change in forest landscapes worldwide. In the Canary Islands, a dense road system fragment the native Canarian pine and laurel forests causing potential changes in population densities of endemic lacertid lizards (genus Gallotia). Our aim was to assess road edge effects on relative abundance patterns of the endemic Gallotia galloti in both forests. We also explored the species–habitat relationships in this road-fragmentation context. We found that lizard relative density in relation to road edges differed between forests. Lizards were more abundant along edges and leeward interior, but virtually absent from the interior of the windward laurel forest. In the pine forest, lizards were present at three distances from edge, with a net decrease in abundance from edge to interior. These patterns may be explained partly by differences in vegetation structure regarding road proximity in each forest that potentially affect the helio- and thigmothermic character of G. galloti, and thus its habitat use. A general suggestion of this study is that road margins create corridors that may be used by native lizards for dispersal through inhospitable forest matrix. The high road density in Tenerife may have negative implications for the conservation of the genetic variability of G. galloti. At the island scale, increased communication between lizard populations through road corridors might increase homogenization of the gene pool. Ecological processes in which this lizard plays important roles may also experience changes along road edges.  相似文献   

7.
8.
The replacement of native forests by Pinus radiata plantations modifies habitat availability and quality for wildlife, constituting a threat to species survival. However, the presence of understory in mature pine plantations minimizes the negative impacts of native forest replacement, rendering a secondary habitat for wildlife. Whether forest-dwelling species recolonize clear-felled areas pending on the spontaneous development of accompanying vegetation growing after harvesting is yet to be assessed. In this context, we analyze the abundance, movement and habitat selection of the endemic ground beetle Ceroglossus chilensis (Coleoptera: Carabidae) in an anthropic forest landscape consisting of native forest remnants, adult pine plantations (>?20 years) with a well-developed understory, and young (1–2 years) pine plantations with varying degrees of accompanying vegetation development. Particularly, we analyze the likelihood that C. chilensis would recolonize young pine plantations depending on the presence (>?70% cover) or the absence (<?20% cover) of this accompanying vegetation. C. chilensis shows a greater probability of selecting habitats with understory (pine plantations and native forest) and young plantations with accompanying vegetation (future understory) than habitats without such vegetation. Movement of C. chilensis also favors their permanence in habitats with understory vegetation, coinciding with higher abundances than in young pine plantations devoid of accompanying vegetation. Hence, the effect of clearcutting could be mitigated by allowing the development of accompanying vegetation into a future understory, which facilitates the recolonization of pine plantations and its use as secondary habitat for wildlife.  相似文献   

9.
Central European calcareous grasslands are considered biodiversity hotspots, but are severely threatened by the change in land-use and by habitat fragmentation. Coniferous forests are typical adjacent habitats to calcareous grasslands, as abandoned calcareous grasslands are often afforested or develop into coniferous forests by succession. To investigate spillover between calcareous grasslands and coniferous forests, a total of 144 pitfall traps for carabid beetles were placed at three different distances (1, 5, 20 m) from the edge in both habitats at eight locations from April to late August. We found that both habitats had a distinct species assemblage and a decrease in spillover with increasing distance from the habitat edge into the adjacent habitat. Calcareous grasslands were more affected by spillover from the adjacent coniferous forests than vice versa because more forest specialists penetrated into calcareous grasslands than grassland specialists penetrated into coniferous forests. We conclude that spillover into small and isolated habitats can severely change species assemblages, which has to be considered in conservation measures. The protection of large sites with small edge-interior ratios can reduce negative effects on species assemblages in endangered calcareous grasslands.  相似文献   

10.
The Palearctic forest-steppe biome is a narrow vegetation zone between the temperate forest and steppe biomes, which provides important habitats for many endangered species and represents an important hotspot of biodiversity. Although the number of studies on forest–grassland mosaics is increasing, information currently available about the general compositional and structural patterns of Eurasian forest-steppes is scarce. Our study aimed to compare the habitat structure, species composition and diversity patterns of two distant sandy forest-steppes of Eurasia. We compared 72 relevés made in the main habitat components (forest, forest edge and grassland) of sandy forest-steppes in three Hungarian and three Kazakh sites. The size of the plots was 25 m2. Species number, Shannon diversity and species evenness values were calculated for each plot. Fidelity calculations and linear mixed effects models were used for the analyses. We found that the vegetation and diversity patterns of the two forest-steppes are similar and their components play important roles in maintaining landscape-scale diversity. Despite the higher species richness in Hungary, Shannon diversity was higher in Kazakhstan. The deciduous forest edges of both areas had significantly higher species richness than the neighbouring habitats (forests and grasslands); therefore they can be considered local biodiversity hotspots. Due to the special characteristics of this vegetation complex, we emphasize the high conservation value of all landscape components as a coherent system throughout the entire range of the Eurasian forest-steppe biome.  相似文献   

11.
Changes in forest productivity across Alaska consistent with biome shift   总被引:1,自引:0,他引:1  
Global vegetation models predict that boreal forests are particularly sensitive to a biome shift during the 21st century. This shift would manifest itself first at the biome's margins, with evergreen forest expanding into current tundra while being replaced by grasslands or temperate forest at the biome's southern edge. We evaluated changes in forest productivity since 1982 across boreal Alaska by linking satellite estimates of primary productivity and a large tree-ring data set. Trends in both records show consistent growth increases at the boreal-tundra ecotones that contrast with drought-induced productivity declines throughout interior Alaska. These patterns support the hypothesized effects of an initiating biome shift. Ultimately, tree dispersal rates, habitat availability and the rate of future climate change, and how it changes disturbance regimes, are expected to determine where the boreal biome will undergo a gradual geographic range shift, and where a more rapid decline.  相似文献   

12.
The correlation between vegetation patterns (species distribution and richness) and altitudinal variation has been widely reported for tropical forests, thereby providing theoretical basis for biodiversity conservation. However, this relationship may have been oversimplified, as many other factors may influence vegetation patterns, such as disturbances, topography and geographic distance. Considering these other factors, our primary question was: is there a vegetation pattern associated with substantial altitudinal variation (10–1,093 m a.s.l.) in the Atlantic Rainforest—a top hotspot for biodiversity conservation—and, if so, what are the main factors driving this pattern? We addressed this question by sampling 11 1-ha plots, applying multivariate methods, correlations and variance partitioning. The Restinga (forest on sandbanks along the coastal plains of Brazil) and a lowland area that was selectively logged 40 years ago were floristically isolated from the other plots. The maximum species richness (>200 spp. per hectare) occurred at approximately 350 m a.s.l. (submontane forest). Gaps, multiple stemmed trees, average elevation and the standard deviation of the slope significantly affected the vegetation pattern. Spatial proximity also influenced the vegetation pattern as a structuring environmental variable or via dispersal constraints. Our results clarify, for the first time, the key variables that drive species distribution and richness across a large altitudinal range within the Atlantic Rainforest.  相似文献   

13.
Landscapes intensively farmed over a long time period represent a threat for natural habitats and high levels of biodiversity. Information on the historical land use and spatial changes of natural habitats can help to explain the causes of a number of contemporary phenomena, which are important for the development of effective conservation and ecosystem management. This case study from the Czech Republic shows that archival written sources describing landscape quality, including vegetation cover, allow the reclassification of old maps to the level of natural habitat categories (sensu Natura 2000), with the aim of analyzing historic changes in land cover. Significant natural habitat decreases began by the middle of the 19th century. Over the course of 250 years, this area of formerly widespread natural wet meadows has declined by 99 %. An area of water vegetation was reduced by 95 %, willow carrs by 98 %, and a mosaic of willow carrs, wet Cirsium meadow, and alder carrs has decreased by 100 %. These decreases were caused by the conversion of meadows, pastures, and ponds into arable lands. Areas of oak-hornbeam forest, acidophilous oak forest, and thermophilous oak forest were primarily converted into monocultures of coniferous trees. Similarly, the areas with alluvial forests decreased. We conclude that old maps and other archive materials, despite their coarse accuracy, can serve as useful tools for disclosing natural habitat changes and their causes, providing a foundation for formulating biodiversity conservation strategies.  相似文献   

14.
Boreal forests are critical to the global carbon (C) cycle. Despite recent advances in our understanding of boreal C budgets, C dynamics during compositional transition to late-succession forests remain unclear. Using a carefully replicated 203-year chronosequence, we examined long-term patterns of forest C stocks and net ecosystem productivity (NEP) following stand-replacing fire in the boreal forest of central Canada. We measured all C pools, including understorey vegetation, belowground biomass, and soil C, which are often missing from C budgets. We found a slight decrease in total ecosystem C stocks during early stand initiation, between 1 and 8 years after fire, at ?0.90 Mg C ha?1 y?1. As stands regenerated, live vegetation biomass increased rapidly, with total ecosystem C stocks reaching a maximum of 287.72 Mg C ha?1 92 years after fire. Total ecosystem C mass then decreased in the 140- and 203-year-old stands, losing between ?0.50 and ?0.74 Mg C ha?1 y?1, contrasting with views that old-growth forests continue to maintain a positive C balance. The C decline corresponded with canopy transition from dominance of Populus tremuloides, Pinus banksiana, and Picea mariana in the 92-year-old stands to Betula papyrifera, Picea glauca, and Abies balsamea in the 203-year-old stands. Results from this study highlight the role of succession in long-term forest C dynamics and its importance when modeling terrestrial C flux.  相似文献   

15.
Forest vegetation has the ability to warm Recent climate by its effects on albedo and atmospheric water vapour, but the role of vegetation in warming climates of the geologic past is poorly understood. This study evaluates the role of forest vegetation in maintaining warm climates of the Late Cretaceous by (1) reconstructing global palaeovegetation for the latest Cretaceous (Maastrichtian); (2) modelling latest Cretaceous climate under unvegetated conditions and different distributions of palaeovegetation; and (3) comparing model output with a global database of palaeoclimatic indicators. Simulation of Maastrichtian climate with the land surface coded as bare soil produces high-latitude temperatures that are too cold to explain the documented palaeogeographic distribution of forest and woodland vegetation. In contrast, simulations that include forest vegetation at high latitudes show significantly warmer temperatures that are sufficient to explain the widespread geographic distribution of high-latitude deciduous forests. These warmer temperatures result from decreased albedo and feedbacks between the land surface and adjacent oceans. Prescribing a realistic distribution of palaeovegetation in model simulations produces the best agreement between simulated climate and the geologic record of palaeoclimatic indicators. Positive feedbacks between high-latitude forests, the atmosphere, and ocean contributed significantly to high-latitude warming during the latest Cretaceous, and imply that high-latitude forest vegetation was an important source of polar warmth during other warm periods of geologic history.  相似文献   

16.
When habitat becomes fragmented, populations of species may become increasingly isolated. In the absence of habitat corridors, genetic structure may develop and populations risk reductions in genetic diversity from increased genetic drift and inbreeding. Deforestation of the Cerrado biome of Brazil, particularly of the dry forests within the Paranã River Basin, has incrementally occurred since the 1970s and increased forest fragmentation within the region. We performed landscape genetic analyses of Pfrimer’s parakeet (Pyrrhura pfrimeri), a globally endangered endemic to the region, to determine if forest fragmentation patterns were associated with genetic structuring in this species. We used previously generated satellite imagery that identified the locations of Paranã River Basin forest fragments in 1977, 1993/94, and 2008. Behavioral data quantifying the affinity of Pfrimer’s parakeet for forest habitat was used to parameterize empirically derived landscape conductance surfaces. Though genetic structure was observed among Pfrimer’s parakeet populations, no association between genetic and geographic distance was detected. Likewise, least cost path lengths, circuit theory-based resistance distances, and a new measure of least cost path length complexity could not be conclusively associated with genetic structure patterns. Instead, a new quantity that encapsulated connection redundancy from the 1977 forest fragmentation data provided the clearest associations with pairwise genetic differentiation patterns (Jost’s D: r = 0.72, P = 0.006; FST: r = 0.741, P = 0.001). Our analyses suggest a 35-year or more lag between deforestation and its effect on genetic structure. Because 66 % of the Paranã River Basin has been deforested since 1977, we expect that genetic structure will increase substantially among Pfrimer’s Parakeet populations in the future, especially if fragmentation continues at its current pace.  相似文献   

17.
Parthenogenetic lineages may colonize marginal areas of the range of related sexual species or coexist with sexual species in the same habitat. Frozen-Niche-Variation and General-Purpose-Genotype are two hypotheses suggesting that competition and interclonal selection result in parthenogenetic populations being either genetically diverse or rather homogeneous. The cosmopolitan parthenogenetic oribatid mite Oppiella nova has a broad ecological phenotype and is omnipresent in a variety of habitats. Morphological variation in body size is prominent in this species and suggests adaptation to distinct environmental conditions. We investigated genetic variance and body size of five independent forest - grassland ecotones. Forests and grasslands were inhabited by distinct genetic lineages with transitional habitats being colonized by both genetic lineages from forest and grassland. Notably, individuals of grasslands were significantly larger than individuals in forests. These differences indicate the presence of specialized genetic lineages specifically adapted to either forests or grasslands which coexist in transitional habitats. Molecular clock estimates suggest that forest and grassland lineages separated 16-6 million years ago, indicating long-term persistence of these lineages in their respective habitat. Long-term persistence, and morphological and genetic divergence imply that drift and environmental factors result in the evolution of distinct parthenogenetic lineages resembling evolution in sexual species. This suggests that parthenogenetic reproduction is not an evolutionary dead end.  相似文献   

18.

Background and aims

Fine root decomposition contributes significantly to element cycling in terrestrial ecosystems. However, studies on root decomposition rates and on the factors that potentially influence them are fewer than those on leaf litter decomposition. To study the effects of region and land use intensity on fine root decomposition, we established a large scale study in three German regions with different climate regimes and soil properties. Methods In 150 forest and 150 grassland sites we deployed litterbags (100 μm mesh size) with standardized litter consisting of fine roots from European beech in forests and from a lowland mesophilous hay meadow in grasslands. In the central study region, we compared decomposition rates of this standardized litter with root litter collected on-site to separate the effect of litter quality from environmental factors.

Results

Standardized herbaceous roots in grassland soils decomposed on average significantly faster (24?±?6 % mass loss after 12 months, mean ± SD) than beech roots in forest soils (12?±?4 %; p?Conclusions Grasslands, which have higher fine root biomass and root turnover compared to forests, also have higher rates of root decomposition. Our results further show that at the regional scale fine root decomposition is influenced by environmental variables such as soil moisture, soil temperature and soil nutrient content. Additional variation is explained by root litter quality.  相似文献   

19.
Understanding wildlife movements and habitat selection are critical to drafting conservation and management plans. We studied a population of eastern Hermann’s tortoise (Testudo hermanni boettgeri) in a traditionally managed rural landscape in Romania, near the northern edge of the species geographic distribution. We used telemetry to radio-track 24 individuals between 2005 and 2008 and performed a Euclidian distance-based habitat selection analysis to investigate habitats preferred by tortoises at both landscapes (second-order order selection) and individual (third-order selection) home range scales. The home range size for tortoises in our study area was 3.79?±?0.62 ha and did not differ by gender or season (pre- and post-nesting seasons). Their movement ecology was characterized by short-distance movements (daily mean?=?31.18?±?1.59 m), apparently unaffected by habitat type. In contrast to other studies, movements of males and females were of similar magnitude. At the landscape (population home range) scale, grasslands and shrubs were preferred, but tortoises also showed affinity to forest edges. At the individual home range scale, tortoises selected grassland and shrub habitats, avoided forests, and used forest edges randomly. Creeks were avoided at both spatial scales. Our results suggest that tortoise home ranges contain well-defined associations of habitats despite a higher selection for grasslands. As such, avoiding land conversion to other uses and maintaining habitat heterogeneity through traditional practices (e.g., manual mowing of grasslands, livestock grazing) are critical for the persistence of tortoise populations.  相似文献   

20.
Floristic differentiation and vegetation definition is an important step to recognize biome distribution and for biodiversity conservation. Here, we aim to verify if the distribution of the costal lowland vegetation in Brazilian littoral is congruent with climatic gradient and the previous vegetation definitions. Additionally we discussed the importance of terms for the Atlantic Forest conservation. Our study was based on floristic and geo-climatic data from 58 published surveys. We generate a checklist of 1088 woody species and verified species distribution according to environmental gradient using a Detrended Correspondence Analysis (DCA). We compared DCA??s groups with the a priori vegetation definition and generate an a posteriori classification using TWINSPAN. DCA and TWINSPAN resulted in groups determined mainly by rainfall (r = ?0.65) and soil sandiness (r = ?0.71). Those groups were not congruent with both the previous vegetation definitions. The coastal lowland vegetation comprises two distinctive floristic groups representing forests and scrubs that occur in wetter climates (Ombrophilous lowland forests) in the Brazilian states of Santa Catarina, Paraná and São Paulo and in drier climates of Espírito Santo, Rio de Janeiro (Restinga-Northern group) and Rio Grande do Sul (Restinga-Southern group) states. The floristic and historical relationships between Ombrophylous lowland forests and Restingas suggest that conservation initiatives should be more conservative and treat collectively all coastal lowland vegetation as a biodiversity hotspot.  相似文献   

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