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Habitat Specificity (habitat + specificity)

Distribution by Scientific Domains

Life Sciences	66%

Selected Abstracts

Habitat specificity and home-range size as attributes of species vulnerability to extinction: a case study using sympatric rattlesnakes

ANIMAL CONSERVATION, Issue 4 2006
J. L. Waldron
Abstract Large home-range size and habitat specificity are two commonly cited ecological attributes that are believed to contribute to species vulnerability. The eastern diamondback rattlesnake Crotalus adamanteus is a declining species that occurs sympatrically with the more abundant canebrake rattlesnake Crotalus horridus in a portion of the south-eastern Coastal Plain, USA. In this study, we use the ecological similarities of the two species as experimental controls to test the role of home-range size and habitat specificity in the imperilment of the eastern diamondback rattlesnake. We used analysis of variance to investigate differences in home-range size between the two species, and home-range selection was modeled as habitat use versus availability with a case control sampling design using logistic regression. We failed to detect differences in home-range size between the two species; therefore, we could not identify home-range size as an attribute contributing to the imperilment of eastern diamondback rattlesnakes. Eastern diamondback rattlesnakes selected pine savannas to a degree that suggests that the species is a habitat specialist. Of the two factors examined, habitat specificity to the imperiled longleaf pine ecosystem may be a significant contributor to the decline of the eastern diamondback rattlesnake. [source]

The verification and application of bioindicators: a case study of dung beetles in a savanna ecosystem

JOURNAL OF APPLIED ECOLOGY, Issue 4 2002
Melodie A. McGeoch
Summary 1Bioindicators of habitat quality and environmental change must be identified quantitatively and tested independently to confirm their usefulness. We used the indicator value (IndVal) method, which combines measures of habitat fidelity and specificity, to assess the indicator responses of dung beetles (Coleoptera: Scarabaeidae) in Tembe Elephant Park, South Africa. The indicator responses were verified by sampling in different areas of the Park, 2 years after the responses were originally quantified. 2We postulated that terrestrial insect indicators with different combinations of habitat specificity and fidelity might fulfil different indicator roles. Indicator species with strong habitat specificity (characteristic species) are unlikely to provide information on the direction of ecological change despite high vulnerability. Rather, detector species that span a range of ecological states are likely to be better in this role. We used IndVal for selecting such detector species that indicate the direction of ecological change. 3Sets of species were found to be robust bioindicators, i.e. reliably characteristic across the habitat of which they were indicative. The suite of indicators was refined by discarding those with IndVals that varied significantly across years, thus improving the confidence in the final suite of species selected. By clearly responding to a change in habitat between two ecological states, detector species provided information complementary to that provided by characteristic species. 4The IndVal method enabled both the identification and testing of indicator (characteristic and detector) species. Because of its resilience to changes in abundance, IndVal is a particularly effective tool for ecological bioindication. 5We conclude that both characteristic and detector species are useful bioindicators of habitat quality and conversion. We propose that bioindicators that are categorized and verified in this way will have valuable application in the monitoring of habitat integrity. [source]

Nested assemblages of Orthoptera species in the Netherlands: the importance of habitat features and life-history traits

JOURNAL OF BIOGEOGRAPHY, Issue 11 2007
M. A. Schouten
Abstract Aim, Species communities often exhibit nestedness, the species found in species-poor sites representing subsets of richer ones. In the Netherlands, where intensification of land use has led to severe fragmentation of nature, we examined the degree of nestedness in the distribution of Orthoptera species. An assessment was made of how environmental conditions and species life-history traits are related to this pattern, and how variation in sampling intensity across sites may influence the observed degree of nestedness. Location, The analysis includes a total of 178 semi-natural sites in the Pleistocene sand region of the Netherlands. Methods, A matrix recording the presence or absence of all Orthoptera species in each site was compiled using atlas data. Additionally, separate matrices were constructed for the species of suborders Ensifera and Caelifera. The degree of nestedness was measured using the binmatnest calculator. binmatnest uses an algorithm to sort the matrices to maximal nestedness. We used Spearman's rank correlations to evaluate whether sites were sorted by area, isolation or habitat heterogeneity, and whether species were sorted by their dispersal ability, rate of development or degree of habitat specificity. Results, We found the Orthoptera assemblages to be significantly nested. The rank correlation between site order and sampling intensity was high. The degree of nestedness was lower, but remained significant when under- and over-sampled sites were excluded from the analysis. Site order was strongly correlated with both size of sample site and number of habitat types per site. Rank correlations showed that species were probably ordered by variation in habitat specificity, rather than by variation in dispersal capacity or rate of development of the species. Main conclusions, Variation in sampling intensity among sites had a strong impact on the observed degree of nestedness. Nestedness in habitats may underlie the observed nestedness within the Orthoptera assemblages. Habitat heterogeneity is closely related to site area, which suggests that several large sites should be preserved, rather than many small sites. Furthermore, the results corroborate a focus of nature conservation policy on sites where rare species occur, as long as the full spectrum of habitat conditions and underlying ecological processes is secured. [source]

Biogeography and conservation of the genus Ficus (Moraceae) in Mexico

JOURNAL OF BIOGEOGRAPHY, Issue 3 2004
Alejandra Serrato
Abstract Aim, The main objective of this study is to document the biogeographical patterns, endemism and degree of conservation of the species of Ficus (Moraceae) in Mexico. There are over 750 species of the genus Ficus distributed worldwide, and Mexico practically represents its northernmost limit in the American continent. Detailed studies at regional scales may help to understand the biogeography of large genera such as Ficus. Location, Mexico. Methods, The biogeographical patterns of Mexican Ficus were obtained from information of fig specimens available in two of the main herbaria of Mexico (2140 vouchers), collecting figs throughout this country, and revising the specialized literature. The presence of each species of Ficus was recorded for every one of Mexico's states and several tropical countries of America. Besides, the Mexican territory was divided into cells of 1° × 1° and the presence or absence of all species of the genus was recorded. Rarity of species was classified based on the width of geographic distribution, habitat specificity and population size. Results, A total of 21 species of Ficus occur in Mexico, including six species (28.6%) that are endemic to this country. Five species are included in subgenus Pharmacosycea and 16 species are documented under subgenus Urostigma. Affinities of Ficus flora with other tropical countries in America generally decreased as geographical distances from Mexico increased. Mexican states and cells with highest values of Ficus species richness (both total and endemic species) were located. Ten species, including three endemics, presented a wide distribution. Five species, including two endemics, possess the three attributes of rarity (narrow geographical distribution, high habitat specificity and scarce local populations). Three species of Ficus, including the endemic and very rare Ficuslapathifolia (Liebm.) Miq., are not recorded in any protected area existing in Mexico. Main conclusions, Most of the Mexican Ficus show a great morphological variation and occupy different habitats along their geographic distribution. The biogeographical patterns described here establish a fundamental scenario for ongoing studies on Ficus,pollinator interactions. However, many local populations are considered to be at risk, as there have been significant reductions in the number and size of local populations. Further studies are needed to understand the process of colonization, maintenance and persistence of fig,pollinator mutualism in species with different patterns of geographic distribution. Mexican Ficus require special policies for conservation due to their complex degree of rarity, particularly their geographic distribution in different types of vegetation, ranging from dry scrublands to tropical rain forests. [source]

Rarity, specialization and extinction in primates

JOURNAL OF BIOGEOGRAPHY, Issue 4 2002
A. H. Harcourt
Aim To determine and explain biological traits that distinguish rare from common primate taxa. Location Africa, Americas, Asia, Madagascar. Methods We compare the biology of rare primate taxa with the biology of common taxa. Rarity is defined by (1) small size of geographic range; (2) small geographic range plus low local population density; and (3) small geographic range plus low local density plus narrow habitat specificity. After a linear comparison of size of geographic range with various biological traits, globally and by realm, extremes of rarity and commonness per realm are identified, and then combined for a global analysis. Tests are done both with genera treated as independent data points (n=62), and also with phylogenetic control by use of an independent contrasts test. Extinction risk in vertebrates, including primates, often correlates with high resource requirements, slow population recovery rate, and specialization. The three indices of rarity are therefore compared with these three general traits. Measures of resource use are body mass, local density, annual range size, and group size; of recovery rate, interbirth interval, and maximum intrinsic rate of natural population increase; and of degree of specialization, variety of diet, of habitats, maximum latitude, and morphological variety. All data come from the literature. Because several measures are compared, probabilities are Bonferroni corrected. Results If rarity in primates correlates with any biological attribute, it consistently correlates with only measures of specialization, and not with measures of high resource use, or slow population recovery rate. Without phylogenetic correction, the first two indices of rarity associate significantly with all four measures of specialization, and the third with maximum latitude. With phylogenetic correction, the first index still associates with all four, the second with two (maximum latitude, number of species per genus), and the third shows no significant associations. While the four measures of specialization are strongly interrelated, stepwise regressions on geographic range indicate that maximum latitude has the strongest effect, followed by dietary variety and number of species per genus and, finally, habitat variety. Main conclusions The most commonly demonstrated traits of susceptibility to extinction are those of high resource use, slow recovery rate, and specialization. Yet, while rarity (almost however, it is defined) is an inevitable precursor to extinction, specialization is the only trait found to correlate with rarity in this study. We cannot explain this apparent contradiction. [source]

Changes in carabid beetle diversity within a fragmented agricultural landscape

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2003
C. N. Magagula
Abstract The distribution of carabid and cicindelid (Coleoptera: Carabidae) beetles in five distinct habitats (riparian, mature orchard, pine windbreak, young orchard, natural veld), within Tambuti Citrus Estate (Swaziland) was examined by pitfall trapping over 18 months. Habitats with high vegetation and litter cover had the highest species diversity and larger specimens, e.g. riparian border and pine windbreak, while the lowest diversity was observed in intensively managed mature citrus orchards. While species such as Tefflus delagorguei Guérin occurred in all the habitats sampled, certain species illustrated habitat specificity; e.g. Dromica ambitiosa Péringuey was observed only in the pine windbreaks while Haplotrachelus sp. Chaudoir occurred mainly in the vegetated riparian and natural veld habitats. Four unidentified carabid beetles were exclusive to the riparian border habitat. This habitat was the only one with a distinct assemblage of species in the agricultural mosaic studied. Multivariate analyses were used to assess the role of soil and environmental variables in relation to the ground beetle diversity within the agricultural mosaic studied. Résumé La distribution des carabes et des cicindèles (Coléoptères: Carabidae) dans cinq habitats distincts (riverain, verger mature, coupe-vent de pins, jeune verger, prairie naturelle) dans le Tambuti Citrus Estate (Swaziland) a été examinée pendant 18 mois au moyen de pièges. Les habitats qui avaient la végétation la plus haute et une litière présentaient la plus forte diversité en espèces et les plus grands spécimens, c'est-à-dire l'habitat riverain et les coupe-vent de pins, tandis qu'on observait la plus faible diversité dans les vergers de citronniers intensément gérés. Alors que des espèces comme Tefflus delagorguei Guérin se retrouvaient dans tous les habitats étudiés, certaines espèces illustraient une certaine spécificité, par exemple Dromica ambitiosa Péringuey, qui n'a été observée que dans les coupe-vent de pins tandis que Haplotrachelus sp. Chaudoir se trouvait surtout dans les habitats riverains et les prairies naturelles. Cinq coléoptères carabidés non identifiés se trouvaient exclusivement dans l'habitat riverain. Cet habitat était le seul à avoir un assemblage d'espèces distinct dans la mosaïque agricole étudiée. Des analyses multivariées ont été utilisées pour évaluer le rôle du sol et des variables environnementales par rapport à la diversité des coléoptères dans le sol de la mosaïque agricole étudiée. [source]

GENETIC DIVERGENCE CORRELATES WITH MORPHOLOGICAL AND ECOLOGICAL SUBDIVISION IN THE DEEP-WATER ELK KELP, PELAGOPHYCUS PORRA (PHAEOPHYCEAE)

JOURNAL OF PHYCOLOGY, Issue 5 2000
Kathy Ann Miller
Pelagophycus porra (Leman) Setchell has a narrow distribution confined to deep water from the Channel Islands off the southern California coast to central Baja California, Mexico. Distinct morphotypes are consistently correlated with distinctive habitats, that is, windward exposures characterized by strong water motion and rocky substrates, and sheltered areas with soft substrates found on the lee sides of the islands. We tested the hypothesis that morphologically and ecologically distinct forms reflect genetically distinct stands. Individuals representing populations from three islands and the mainland were compared using RFLP analyses of the nuclear rDNA internal transcribed spacers (ITS1 and ITS2), chloroplast trnL (UAA) intron sequences, and random amplified polymorphic DNA (RAPDs). No variation was found in a survey of 20 restriction sites of ITS1 (ca. 320 base pair [bp]) and ITS2 (ca. 360 bp) among individuals from six populations. Likewise, comparisons of trnL intron (241 bp) sequences among nine individuals from seven populations were identical with the exception of a CATAGT insert in two adjacent stands. A RAPD analysis of 24 individuals from nine populations (4 windward and 5 leeward) using 16 primers generated 166 bands. Thirty-eight percent of the bands did not vary, 16% were unique to a given individual, and 46% were variable. Neighbor joining analysis produced a well-resolved tree with moderately high bootstrap support in which windward and leeward populations were easily distinguished. The lack of divergence in both the fast evolving nuclear rDNA-ITS and the chloroplast trnL intron does not support the morphotypes as different species. However, the compartmentalized differentiation shown in the RAPD data clearly points to isolation. This, and previous ecological studies that demonstrate habitat specificity suggest that leeward stands probably comprise a species in statu nascendi. [source]

Cryptic speciation and patterns of phenotypic variation of a highly variable acanthocephalan parasite

MOLECULAR ECOLOGY, Issue 19 2007
M. L. STEINAUER
Abstract An investigation of a parasite species that is broadly host- and habitat-specific and exhibits alternative transmission strategies was undertaken to examine intraspecific variability and if it can be attributed to cryptic speciation or environmentally induced plasticity. Specimens of an acanthocephalan parasite, Leptorhynchoides thecatus, collected throughout North America were analysed phylogenetically using sequences of the cytochrome oxidase I gene and the internal transcribed spacer region. Variation in host use, habitat use, and transmission were examined in a phylogenetic context to determine if they were more likely phylogenetically based or due to environmental influences. Results indicated that most of the variation detected can be explained by the presence of cryptic species. The majority of these species have narrow host and microhabitat specificities although one species, which also may comprise a complex of species, exhibits broad host and habitat specificity. Alternate transmission pathways only occurred in two of the cryptic species and correlate with host use patterns. Taxa that mature in piscivorous piscine hosts use a paratenic fish host to bridge the trophic gap between their amphipod intermediate host and piscivorous definitive host. One potential example of environmentally induced variation was identified in three populations of these parasites, which differ on their abilities to infect different host species. [source]

Habitat specificity and home-range size as attributes of species vulnerability to extinction: a case study using sympatric rattlesnakes

Terrestrial Small Mammal Richness and Habitat Associations in an Amazon Forest,Cerrado Contact Zone,

BIOTROPICA, Issue 1 2001
Thomas E. Lacher Jr.
ABSTRACT The Amazon Forest and the Cerrado of central Brazil share an extensive zone of integration. Each of these major ecosystems remains poorly studied; however, the composition of communities at the contact zone is even less well described. Small mammals were sampled during a ten,week period in a zone of contact between Amazonian forest and Cerrado. The vegetation in the area was a complex mixture of tropical and semi,deciduous forest, and grassland and savanna woodland formations. Mammals were marked and recaptured on 0.25, to 0.5,km transects and vouchers were collected. A total of 19 species was caught (13 rodents and 6 marsupials) in 4621 trap nights. Transitions from one vegetation type to another were abrupt with ecotones frequently < 5 m in width. The highest a,diversity was 7 species in cerrado. Ten of the 19 species were restricted to one habitat and 6 were restricted to two habitats. Three generalist grassland species occurred in more than two habitats, all variations of savanna. These data support other research indicating high habitat specificity of vertebrates and plants in the Brazilian savannas. The diversity of habitats within reserves in tropical grasslands must be given consideration in the design of protected areas in order to maximize the conservation of mammalian biodiversity. RESUMES A floresta Amazônica e o Cerrado do Brasil Central compartilham uma zona extensa de integração. Estes ecossistemas são pouco estudados, e a composição das comunidades que ocorrem na zona de contato é ainda menos conhecida. Pequenos mamiferos foram capturados durance um período de 10 semanas em uma zona de contato entre a floresta Amazônica e o Cerrado. A vegetação desta área é um complexo de florestas semidecíduas e tropicais, campos e cerrados. Mamiferos foram capturados e marcados em transetos variando de 250 a 500 m; uma coleção de referênda também foi feita. Capturamos um total de 19 espécies (13 roedores e 6 marsupiais) em 4621 noitesarmadilhas. As transições entre tipos de vegetação foram abruptas com ecótonos frequentemente menores que 5 m de largura. O cerrado teve a a-diversidade mais alta: sete espécies. Dez das 19 espécies estavam restritas a um habitat e seis a dois habitats. Três espécies generalistas de savana ocorreram em mais de dois habitats, mas sempre em algum tipo de campo ou cerrado aberto. Estes dados corroboram com outras pesquisas indicando um alto nivel de especificidade de habitat para vertebrados e plantas no Cerrado. Consequentemente, para melhor preservar a diversidade de mamíferos no Brasil Central deve-se dar mais atenção à diversidade de habitats em áreas de proteção no Cerrado. [source]