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Habitat Generalists (habitat + generalist)

Distribution by Scientific Domains

Life Sciences	88%

Distribution within Life Sciences

Conservation Science	50%
Ecology & Organismal Biology	25%

Selected Abstracts

Are forest birds categorised as "edge species" strictly associated with edges?

ECOGRAPHY, Issue 4 2003
Louis Imbeau
In recent years, studies of bird-habitat relationships undertaken in the context of habitat fragmentation have led to the widespread use of species categorisation according to their response to edge alongside mature forest patches (edge species, interior species, interior-edge generalist species). In other research contexts, especially in less fragmented landscapes dominated by a forested land base in various age classes, bird-habitat relationships are often described in relation to their use of various successional stages (early-successional species, mature forest species, generalist species). A simple comparison of these two commonly-used classifications schemes in a close geographical range for 60 species in eastern North America as well as for 36 species in north-western Europe clearly reveals that in these two particular biomes the two classifications are not independent. We believe that this association is not only a semantic issue and has important ecological consequences. For example, almost all edge species are associated with early-successional habitats when a wide range of forest age-classes are found in a given area. Accordingly, we suggest that most species considered to prefer edge habitats in agricultural landscapes are in fact only early-successional species that could not find shrubland conditions apart from the exposed edges of mature forest fragments. To be considered a true edge species, a given species should require the simultaneous availability of more than one habitat type and consequently should be classified as a habitat generalist in its use of successional stages. However, 28 out of 30 recognised edge species were considered habitat specialists in terms of successional status. Based on these results, we conclude that "real edge species" are probably quite rare and that we should make a difference between true edge species and species which in some landscapes, happen to find their habitat requirements on edges. [source]

Performance Trade-offs Driven by Morphological Plasticity Contribute to Habitat Specialization of Bornean Tree Species

BIOTROPICA, Issue 4 2009
Daisy H. Dent
ABSTRACT Growth-survival trade-offs play an important role in niche differentiation of tropical tree species in relation to light-gradient partitioning. However, the mechanisms that determine differential species performance in response to light and soil resource availability are poorly understood. To examine responses to light and soil nutrient availability, we grew seedlings of five tropical tree species for 12 mo at < 2 and 18 percent full sunlight and in two soil types representing natural contrasts in nutrient availability within a lowland dipterocarp forest in North Borneo. We chose two specialists of nutrient-rich and nutrient-poor soils, respectively, and one habitat generalist. Across all species, growth was higher in high than low light and on more nutrient rich soil. Although species differed in growth rates, the ranking of species, in terms of growth, was consistent across the four treatments. Nutrient-rich soils improved seedling survival and increased growth of three species even under low light. Slower-growing species increased root allocation and reduced specific leaf area (SLA) and leaf area ratio (LAR) in response to decreased nutrient supply. All species increased LAR in response to low light. Maximum growth rates were negatively correlated with survival in the most resource-limited environment. Nutrient-poor soil specialists had low maximum growth rates but high survival at low resource availability. Specialists of nutrient-rich soils, plus the habitat generalist, had the opposite suite of traits. Fitness component trade-offs may be driven by both light and belowground resource availability. These trade-offs contribute to differentiation of tropical tree species among habitats defined by edaphic variation. [source]

Conservation of Insect Diversity: a Habitat Approach

CONSERVATION BIOLOGY, Issue 6 2000
Jennifer B. Hughes
To explore the feasibility of basing conservation action on community-level biogeography, we sampled a montane insect community. We addressed three issues: (1) the appropriate scale for sampling insect communities; (2) the association of habitat specialization,perhaps a measure of extinction vulnerability,with other ecological or physical traits; and (3) the correlation of diversity across major insect groups. Using malaise traps in Gunnison County, Colorado, we captured 8847 Diptera (identified to family and morphospecies), 1822 Hymenoptera (identified to morphospecies), and 2107 other insects (identified to order). We sampled in three habitat types,meadow, aspen, and conifer,defined on the basis of the dominant vegetation at the scale of hundreds of meters. Dipteran communities were clearly differentiated by habitat type rather than geographic proximity. This result also holds true for hymenopteran communities. Body size and feeding habits were associated with habitat specialization at the family level. In particular, habitat generalists at the family level,taxa perhaps more likely to survive anthropogenic habitat alteration,tended to be trophic generalists. Dipteran species richness was marginally correlated with hymenopteran species richness and was significantly correlated with the total number of insect orders sampled by site. Because these correlations result from differences in richness among habitat types, insect taxa may be reasonable surrogates for one another when sampling is done across habitat types. In sum, community-wide studies appear to offer a practical way to gather information about the diversity and distribution of little-known taxa. Resumen:No existe ni el tiempo ni los recursos para diseñar planes de conservación para cada especie, particularmente para los taxones poco estudiados, no carismáticas, pero ecológicamente importantes que componen la mayoría de la biodiversidad. Para explorar la factibilidad de basar acciones de conservación en biogegrafía a nivel comunitario, muestreamos una comunidad de insectos de montaña. Evaluamos tres aspectos: (1) la escala adecuada para el muestreo de comunidades de insectos; (2) la asociación de especialización de hábitat,quizá una medida de vulnerabilidad de extinción,con otras características ecológicas o físicas; y (3) la correlación de la diversidad a lo largo de los grupos principales de insectos. Mediante el uso de trampas en el condado Gunnison, en Colorado, capturamos 8847 dípteros (identificados a nivel de familia y morfoespecies), 1822 himenópteros (identificadas hasta morfoespecies) y 2107 otros insectos (identificados a nivel de orden). Muestreamos tres tipos de hábitats,vega, álamos temblones y coníferas,definidos en base a la vegetación dominante a escala de cientos de metros. Las comunidades de dípteros estuvieron claramente diferenciadas por tipos de hábitat y no por la proximidad geográfica. Este resultado también se mantiene para las comunidades de himenópteros. El tamaño del cuerpo y los hábitos alimenticios estuvieron asociados con la especialización del hábitat a nivel de familia. En particular, los generalistas de hábitat a nivel de familia,los taxones que posiblemente tengan mayor probabilidad de sobrevivir alteraciones antropogénicas del hábitat,tendieron a ser generalistas tróficos. La riqueza de las especies de dípteros estuvo marginalmente correlacionada con la riqueza de especies de himenópteros y estuvo significativamente correlacionada con el número total de órdenes de insectos muestreadas por sitio. Debido a que estas correlaciones resultaron de diferencias en la riqueza de especies entre tipos de hábitats, los taxones de insectos podrían ser substitutos mutuos razonables cuando se muestrea entre diferentes tipos de hábitats. En resumen, los estudios a lo largo de comunidades parecen ofrecer una forma práctica de recolectar información sobre la diversidad y distribución de los taxones poco estudiados. [source]

Effects of Fragmentation of Araucarian Vine Forest on Small Mammal Communities

CONSERVATION BIOLOGY, Issue 4 2000
Jocelyn M. Bentley
We examined the abundance of small mammal species in forests, corridors, remnants of araucarian vine forest, and Araucaria cunninghamii plantations and pastures. None of the forest mammal species persisted following conversion of forest to pasture. Plantations supported lowered abundances of a subset of forest species that were mainly habitat generalists with respect to their occurrence in different floristic types of undisturbed native forest. Within plantations, an increased subcanopy cover was associated with a more forest-like small mammal assemblage. Species' responses to habitat fragmentation varied. The floristic habitat generalists were largely tolerant of habitat fragmentation, their abundance being similar in forests, corridors, and remnants, and were capable of persisting in remnants a few hectares in area. Floristic habitat specialists were vulnerable to habitat fragmentation and thus were abundant in continuous forest, were less abundant in corridors, and were generally absent from remnants. Species that avoid the corridor matrix and are therefore constrained to the corridor may be disadvantaged by the linearity of the habitat, consistent with the predictions of central-place foraging theory. Although small remnants and corridors provide habitat for some species, those that are more specialized in their use of undisturbed habitat types require the retention or reestablishment of large intact areas. Resumen: La pérdida de hábitat y la fragmentación son amenazas importantes para la sobrevivencia de la fauna que depende del bosque. Examinamos la abundancia de especies de mamíferos pequeños en bosques, corredores, y en remanentes de bosques de vid araucarios y en plantaciones de Araucaria cunninghamii y pastizales. Ninguna de las especies de mamíferos del bosque persistió después de la conversión del bosque a pastizal. Las plantaciones favorecieron abundancias menores de un conjunto de especies del bosque integrado principalmente por generalistas de hábitat con respecto a su presencia en diferentes tipos florísticos de bosque nativo sin perturbar. Dentro de las plantaciones, cuanto mayor era la cobertura por debajo del dosel más se parecía el ensamblaje de mamíferos pequeños al del bosque. Las respuestas de las especies a la fragmentación del hábitat fueron variadas. Los generalistas del hábitat florístico por lo general toleraban la fragmentación del hábitat ( la abundancia en bosques, corredores y remanentes era similar) y fueron capaces de persistir en remanentes de unas pocas hectáreas de extensión. Los especialistas de hábitat florístico fueron vulnerables a la fragmentación del hábitat y por ello fueron más abundantes en bosques continuos, menos abundantes en corredores y generalmente ausentes en los remanentes. Las especies que evitaron la matriz de corredores y por lo tanto se encuentran limitadas al corredor pueden estar en desventaja por la linearidad del hábitat, consistente con las predicciones de la teoría del forrajeo de sitio central. A pesar de que los remanentes pequeños y los corredores proveen hábitat para algunas especies, aquéllas que son más especializadas en el uso de tipos de hábitat sin perturbar requieren de la retención o del restablecimiento de áreas intactas grandes. [source]

Spatiotemporal changes of beetle communities across a tree diversity gradient

DIVERSITY AND DISTRIBUTIONS, Issue 4 2009
Stephanie Sobek
Abstract Aim, Plant and arthropod diversity are often related, but data on the role of mature tree diversity on canopy insect communities are fragmentary. We compare species richness of canopy beetles across a tree diversity gradient ranging from mono-dominant beech to mixed stands within a deciduous forest, and analyse community composition changes across space and time. Location, Germany's largest exclusively deciduous forest, the Hainich National Park (Thuringia). Methods, We used flight interception traps to assess the beetle fauna of various tree species, and applied additive partitioning to examine spatiotemporal patterns of diversity. Results, Species richness of beetle communities increased across the tree diversity gradient from 99 to 181 species per forest stand. Intra- and interspecific spatial turnover among trees contributed more than temporal turnover among months to the total ,-beetle diversity of the sampled stands. However, due to parallel increases in the number of habitat generalists and the number of species in each feeding guild (herbivores, predators and fungivores), no proportional changes in community composition could be observed. If only beech trees were analysed across the gradient, patterns were similar but temporal (monthly) species turnover was higher compared to spatial turnover among trees and not related to tree diversity. Main conclusions, The changes in species richness and community composition across the gradient can be explained by habitat heterogeneity, which increased with the mix of tree species. We conclude that understanding temporal and spatial species turnover is the key to understanding biodiversity patterns. Mono-dominant beech stands are insufficient to conserve fully the regional species richness of the remaining semi-natural deciduous forest habitats in Central Europe, and analysing beech alone would have resulted in the misleading conclusion that temporal (monthly) turnover contributes more to beetle diversity than spatial turnover among different tree species or tree individuals. [source]

Size-related deterioration of semi-natural grassland fragments in Sweden

DIVERSITY AND DISTRIBUTIONS, Issue 1 2002
Katariina Kiviniemi
Abstract. One of the most dramatic landscape changes during the 20th century in Sweden, like in most of Europe, has been the reduction and fragmentation of semi-natural grasslands. Using a set of remnant semi-natural grasslands, chosen to be as similar as possible, but differing in size, we have examined whether size of remnant fragments of traditionally managed semi-natural grasslands in Sweden is related to patterns of species richness and composition. We focused on edge-to-interior relationships, since we expected that a possible impact from invasive habitat generalists would be manifested in a gradient from the edge of fragments to their interior. We found no relationship between size of grassland fragments and (a) overall species richness, (b) species richness at different spatial scales, and (c) abundance of some typical invader species or species characteristic of semi-natural grasslands. However, the results indicated that larger grasslands have a comparatively larger number of species in the edges, whereas the opposite pattern was found in smaller grasslands. The similarity in species composition between the edge and the interior of the pastures also increased with grassland size. Thus, even though the overall species richness is still unaffected by reduction in grassland fragment size, the edges of smaller grasslands show signs of degradation, i.e. reduction in species richness and a decreased similarity to the grassland interior. We suggest that these kinds of effects may be early signs of fragmentation effects that in the future will result in species loss even if the present distribution of semi-natural grasslands is maintained. [source]

Interspecific differences in population trends of Spanish birds are related to habitat and climatic preferences

GLOBAL ECOLOGY, Issue 1 2008
Javier Seoane
ABSTRACT Aim, Animal monitoring programmes have allowed analyses of population trends, most of which now comment on the possible effect of global climate change. However, the relationship between the interspecific variation in population trends and species traits, such as habitat preferences, niche breadth or distribution patterns, has received little attention, in spite of its usefulness in the construction of ecological generalizations. The objectives of this study were: (1) to determine whether there are characteristics shared among species with upwards or downwards trends, and (2) to assess whether population changes agree with what could be expected under global warming (a decrease in species typical of cooler environments). Location, The Spanish part of the Iberian Peninsula (c. 500,000 km2) in the south-western part of the Mediterranean Basin. Methods, We modelled recent breeding population changes (1996,2004), in areas without apparent land use changes, for 57 common passerine birds with species-specific ecological and distributional patterns as explanatory variables. Results, One-half of these species have shown a generalized pattern towards the increase of their populations, while only one-tenth showed a significant decrease. One half (54%) of the interspecific variability in yearly population trends is explained considering species-specific traits. Species showing more marked increases preferred wooded habitats, were habitat generalists and occupied warmer and wetter areas, while moderate decreases were found for open country habitats in drier areas. Main conclusions, The coherent pattern in population trends we found disagrees with the proposed detrimental effect of global warming on bird populations of western Europe, which is expected to be more intense in bird species inhabiting cooler areas and habitats. Such a pattern suggests that factors other than the increase in temperature may be brought to discussions on global change as relevant components to explain recent changes in biodiversity. [source]

Using GIS to relate small mammal abundance and landscape structure at multiple spatial extents: the northern flying squirrel in Alberta, Canada

JOURNAL OF APPLIED ECOLOGY, Issue 3 2005
MATTHEW WHEATLEY
Summary 1It is common practice to evaluate the potential effects of management scenarios on animal populations using geographical information systems (GIS) that relate proximate landscape structure or general habitat types to indices of animal abundance. Implicit in this approach is that the animal population responds to landscape features at the spatial grain and extent represented in available digital map inventories. 2The northern flying squirrel Glaucomys sabrinus is of particular interest in North American forest management because it is known from the Pacific North-West as a habitat specialist, a keystone species of old-growth coniferous forest and an important disperser of hypogeous, mycorrhizal fungal spores. Using a GIS approach we tested whether the relative abundance of flying squirrel in northern Alberta, Canada, is related to old forest, conifer forest and relevant landscape features as quantified from management-based digital forest inventories. 3We related squirrel abundance, estimated through live trapping, to habitat type (forest composition: conifer, mixed-wood and deciduous) and landscape structure (stand height, stand age, stand heterogeneity and anthropogenic disturbance) at three spatial extents (50 m, 150 m and 300 m) around each site. 4Relative abundances of northern flying squirrel populations in northern and western Alberta were similar to those previously reported from other regions of North America. Capture rates were variable among sites, but showed no trends with respect to year or provincial natural region (foothills vs. boreal). 5Average flying squirrel abundance was similar in all habitats, with increased values within mixed-wood stands at large spatial extents (300 m) and within deciduous-dominated stands at smaller spatial extents (50 m). No relationship was found between squirrel abundance and conifer composition or stand age at any spatial extent. 6None of the landscape variables calculated from GIS forest inventories predicted squirrel abundance at the 50-m or 150-m spatial extents. However, at the 300-m spatial extent we found a negative, significant relationship between average stand height and squirrel abundance. 7Synthesis and applications. Boreal and foothill populations of northern flying squirrel in Canada appear unrelated to landscape composition at the relatively large spatial resolutions characteristic of resource inventory data commonly used for management and planning in these regions. Flying squirrel populations do not appear clearly associated with old-aged or conifer forests; rather, they appear as habitat generalists. This study suggests that northern, interior populations of northern flying squirrel are probably more related to stand-level components of forest structure, such as food, microclimate (e.g. moisture) and understorey complexity, variables not commonly available in large-scale digital map inventories. We conclude that the available digital habitat data potentially exclude relevant, spatially dependent information and could be used inappropriately for predicting the abundance of some species in management decision making. [source]

Historical and contemporary distributions of carnivores in forests of the Sierra Nevada, California, USA

JOURNAL OF BIOGEOGRAPHY, Issue 8 2005
William J. Zielinski
Abstract Aim, Mammalian carnivores are considered particularly sensitive indicators of environmental change. Information on the distribution of carnivores from the early 1900s provides a unique opportunity to evaluate changes in their distributions over a 75-year period during which the influence of human uses of forest resources in California greatly increased. We present information on the distributions of forest carnivores in the context of two of the most significant changes in the Sierra Nevada during this period: the expansion of human settlement and the reduction in mature forests by timber harvest. Methods, We compare the historical and contemporary distributions of 10 taxa of mesocarnivores in the conifer forests of the Sierra Nevada and southern Cascade Range by contrasting the distribution of museum and fur harvest records from the early 1900s with the distribution of detections from baited track-plate and camera surveys conducted from 1996 to 2002. A total of 344 sample units (6 track plates and 1 camera each) were distributed systematically across c. 3,000,000 ha area over a 7-year period. Results, Two species, the wolverine (Gulo gulo) and the red fox (Vulpes vulpes), present in the historical record for our survey area, were not detected during the contemporary surveys. The distributions of 3 species (fisher [Martespennanti], American marten [M. americana], and Virginia opossum [Didelphisvirginiana]) have substantially changed since the early 1900s. The distributions of fishers and martens, mature-forest specialists, appeared to have decreased in the northern Sierra Nevada and southern Cascade region. A reputed gap in the current distribution of fishers was confirmed. We report for the first time evidence that the distribution of martens has become fragmented in the southern Cascades and northern Sierra Nevada. The opossum, an introduced marsupial, expanded its distribution in the Sierra Nevada significantly since it was introduced to the south-central coast region of California in the 1930s. There did not appear to be any changes in the distributions of the species that were considered habitat generalists: gray fox (Urocyon cinereoargenteus), striped skunk (Mephitis mephitis), western spotted skunk (Spilogale gracilis), or black bear (Ursus americanus). Detections of raccoons (Procyon lotor) and badgers (Taxidea taxus) were too rare to evaluate. Contemporary surveys indicated that weasels (M. frenata and M. erminea) were distributed throughout the study area, but historical data were not available for comparison. Main conclusions, Two species, the wolverine and Sierra Nevada red fox, were not detected in contemporary surveys and may be extirpated or in extremely low densities in the regions sampled. The distributions of the mature forest specialists (marten and fisher) appear to have changed more than the distributions of the forest generalists. This is most likely due to a combination of loss of mature forest habitat, residential development and the latent effects of commercial trapping. Biological characteristics of individual species, in combination with the effect of human activities, appear to have combined to affect the current distributions of carnivores in the Sierra Nevada. Periodic resampling of the distributions of carnivores in California, via remote detection methods, is an efficient means for monitoring the status of their populations. [source]