RESUMO
Species sensitivity to forest fragmentation varies latitudinally, peaking in the tropics. A prominent explanation for this pattern is that historical landscape disturbance at higher latitudes has removed fragmentation-sensitive species or promoted the evolution of more resilient survivors. However, it is unclear whether this so-called extinction filter is the dominant driver of geographic variation in fragmentation sensitivity, particularly because climatic factors may also cause latitudinal gradients in dispersal ability, a key trait mediating sensitivity to habitat fragmentation. Here we combine field survey data with a morphological proxy for avian dispersal ability (hand-wing index) to assess responses to forest fragmentation in 1,034 bird species worldwide. We find that fragmentation sensitivity is strongly predicted by dispersal limitation and that other factors-latitude, body mass and historical disturbance events-have relatively limited explanatory power after accounting for species differences in dispersal. We also show that variation in dispersal ability is only weakly predicted by historical disturbance and more strongly associated with intra-annual temperature fluctuations (seasonality). Our results suggest that climatic factors play a dominant role in driving global variation in the impacts of forest fragmentation, emphasizing the need for more nuanced environmental policies that take into account local context and associated species traits.
Assuntos
Ecossistema , Florestas , Animais , Clima , Aves/fisiologia , Política AmbientalRESUMO
Models used to explain the social organization of primates suggest that variation in daily path length (DPL) is a response to variation in resource distribution and the intensity of intragroup feeding competition. However, daily path length may be affected by a number of other factors including the availability and distribution of nutritionally complementary food items, temperature which can influence activity budget, patterns of subgrouping, and the frequency and function of intergroup encounters. In this 6-month study (total 495 hr of quantitative data), we examined daily path lengths in two neighboring groups of black and gold howler monkeys (Alouatta caraya) inhabiting a semi-deciduous gallery forest in San Cayetano (27° 30'S, 58° 41'W), in the northwest province of Corrientes, Argentina. Both study groups were of similar size and composition. We identified relationships across groups between time spent feeding on fruits, leaves, and flowers, the number of trees visited, group spread, frequency of intergroup encounters, mean daily temperature, and DPL. Our results suggest that variation in food availability had a significant impact on howler ranging behavior by increasing DPL under conditions of high immature and mature fruit availability, and by decreasing DPL with increased availability and increased time invested in feeding on mature leaves. These results do not support the contention that a reduction in food availability or an increase in within-group feeding competition increased DPL in black and gold howler monkeys. DPL in black and gold howlers is influenced by several interrelated factors. In this regard we suggest that models of socio-ecology and ecological constraints need to reconsider how factors such as individual nutritional requirements, social tolerance and group cohesion, and the spatial and temporal availability of preferred and nearby food resources influence primate ranging behavior. Am. J. Primatol. 78:825-837, 2016. © 2016 Wiley Periodicals, Inc.
Assuntos
Alouatta , Comportamento Social , Animais , Argentina , Comportamento Alimentar , Florestas , Ouro , ÁrvoresRESUMO
Habitat fragmentation studies have produced complex results that are challenging to synthesize. Inconsistencies among studies may result from variation in the choice of landscape metrics and response variables, which is often compounded by a lack of key statistical or methodological information. Collating primary datasets on biodiversity responses to fragmentation in a consistent and flexible database permits simple data retrieval for subsequent analyses. We present a relational database that links such field data to taxonomic nomenclature, spatial and temporal plot attributes, and environmental characteristics. Field assessments include measurements of the response(s) (e.g., presence, abundance, ground cover) of one or more species linked to plots in fragments within a partially forested landscape. The database currently holds 9830 unique species recorded in plots of 58 unique landscapes in six of eight realms: mammals 315, birds 1286, herptiles 460, insects 4521, spiders 204, other arthropods 85, gastropods 70, annelids 8, platyhelminthes 4, Onychophora 2, vascular plants 2112, nonvascular plants and lichens 320, and fungi 449. Three landscapes were sampled as long-term time series (>10 years). Seven hundred and eleven species are found in two or more landscapes. Consolidating the substantial amount of primary data available on biodiversity responses to fragmentation in the context of land-use change and natural disturbances is an essential part of understanding the effects of increasing anthropogenic pressures on land. The consistent format of this database facilitates testing of generalizations concerning biologic responses to fragmentation across diverse systems and taxa. It also allows the re-examination of existing datasets with alternative landscape metrics and robust statistical methods, for example, helping to address pseudo-replication problems. The database can thus help researchers in producing broad syntheses of the effects of land use. The database is dynamic and inclusive, and contributions from individual and large-scale data-collection efforts are welcome.
RESUMO
Modified-habitat use by tropical forest-dependent birds in the Caribbean region of Guatemala. As natural areas are reduced into isolated remnants, the importance of secondary habitats for species conservation will increase. Consequently, the conservation value of human-modified or created secondary habitats must be determined. In this study, we evaluated the conservation potential of three habitats associated to cattle ranching (riparian forest, live fence, and pasture) for tropical forest birds in the Caribbean region of Guatemala. We studied the bird communities of five tropical forest and riparian forest (henceforth river) sites, three live fence sites and four pasture sites, in five cattle ranches in the region, and compared the four habitats based on the following parameters: species richness, number of individuals, species composition and an index of conservation importance. A 10-point series was sampled (six repetitions of each series) in each habitat site using the point-count method, in march and april of 1998 and 1999. Although forest, river and live fence had similar mean species numbers, considering all species (111, 96 and 94 species, respectively), and river and live fence surpassed the forest in mean number of individuals (80 and 72 compared to 56 individuals), river and live fence had significantly fewer mean numbers of interior-forest resident species and individuals (56, 21 and 15 species, and 61, 19 and eight individuals in forest, river and live fence, respectively). River and live fence, when compared to forest, had no significant differences in the number of resident forest-edge species and individuals, but their edge-species composition was significantly different from forest. Those resident edge species that were relatively abundant in forest had very low abundances in the modified habitats, and those that were abundant in river and live fence were rare or absent in forest sites. With respect to migratory species, both river and live fence were very important, and the river was more important than forest, according to the conservation importance index. We conclude that these modified habitats have very little value for tropical forest-dependent resident species, but are extremely important for migratory species, particularly those of arboreal habits. We also stress that the conservation importance of alternative habitats should be based on species composition, as opposed to species richness and abundance, and defined as a function of species of particular conservation importance, in our locality, those dependent of tropical lowland forest.
Assuntos
Aves/classificação , Ecossistema , Árvores , Animais , Biodiversidade , Bovinos , Guatemala , Humanos , Densidade Demográfica , Clima TropicalRESUMO
Modified-habitat use by tropical forest-dependent birds in the Caribbean region of Guatemala. As natural areas are reduced into isolated remnants, the importance of secondary habitats for species conservation will increase. Consequently, the conservation value of human-modified or created secondary habitats must be determined. in this study, we evaluated the conservation potential of three habitats associated to cattle ranching (riparian forest, live fence, and pasture) for tropical forest birds in the Caribbean region of Guatemala. We studied the bird communities of five tropical forest and riparian forest (henceforth river) sites, three live fence sites and four pasture sites, in five cattle ranches in the region, and compared the four habitats based on the following parameters: species richness, number of individuals, species composition and an index of conservation importance. A 10-point series was sampled (six repetitions of each series) in each habitat site using the point-count method, in march and april of 1998 and 1999. Although forest, river and live fence had similar mean species numbers, considering all species (111, 96 and 94 species, respectively), and river and live fence surpassed the forest in mean number of individuals (80 and 72 compared to 56 individuals), river and live fence had significantly fewer mean numbers of interior-forest resident species and individuals (56, 21 and 15 species, and 61, 19 and eight individuals in forest, river and live fence, respectively). River and live fence, when compared to forest, had no significant differences in the number of resident forest-edge species and individuals, but their edge-species composition was significantly different from forest. Those resident edge species that were relatively abundant in forest had very low abundances in the modified habitats, and those that were abundant in river and live fence were rare or absent in forest sites. With respect to migratory species, both river and live fence were very important, and the river was more important than forest, according to the conservation importance index. We conclude that these modified habitats have very little value for tropical forest-dependent resident species, but are extremely important for migratory species, particularly those of arboreal habits. We also stress that the conservation importance of alternative habitats should be based on species composition, as opposed to species richness and abundance, and defined as a function of species of particular conservation importance, in our locality, those dependent of tropical lowland forest. Rev. Biol. Trop. 57 (1-2): 401-419. Epub 2009 June 30.
A medida que las áreas de vegetación natural en los neotrópicos estén siendo reducidas a remanentes aislados, la importancia de la vegetación secundaria para la conservación de especies aumentará. Por lo tanto, debe determinarse el valor de los hábitats modificados o creados por el hombre para la conservación de especies dependientes de hábitats originales. En este estudio, evaluamos el valor para la conservación de tres hábitats asociados a la ganadería (bosque ribereño, cerco vivo y pastizal) para las aves típicas de bosque tropical en la región caribeña de Guatemala. Estudiamos las comunidades de aves de cinco sitios de bosque tropical bajo y bosque ribereño (río), tres sitios de cerco vivo y cuatro de pastizales, en cinco fincas ganaderas de la región, y comparamos los cuatro hábitats en función de los siguientes parámetros: número de especies, número de individuos, composición de especies, e índice de importancia. Una serie de 10 puntos de conteo se evaluó (seis repeticiones de cada serie) en cada hábitat, durante abril y mayo de 1998 y 1999. Aunque el número de especies fue similar en bosque, río y cerco vivo (111, 96 y 94 especies, respectivamente), y el río y cerco vivo superaron al bosque en el número de individuos (80 y 72, comparado a 56 individuos), el río y cerco vivo tuvieron números de especies e individuos de residentes de interior de bosque significativamente menores a los del bosque (56, 21 y 15 especies y 61, 19 y 8 individuos en bosque, río y cerco, respectivamente). El río y cerco vivo no se diferenciaron en el número de especies e individuos residentes de borde de bosque, pero la composición de las comunidades de este grupo de especies fue significativamente distinta entre estos dos hábitats y el bosque. Las especies de borde que fueron relativamente abundantes en bosque tuvieron abundancias muy bajas en los hábitats modificados, y aquellas que fueron abundantes en río y cerco vivo estaban prácticamente ausentes en el bosque tropical y fueron generalistas. Con respecto a las especies migratorias, tanto el río como el cerco vivo resultaron ser muy importantes para éstas, y el río incluso fue más importante que el bosque tropical. Concluimos que estos hábitats modificados tienen muy poco valor de conservación para las especies residentes típicas de bosque tropical, pero resultan ser muy importantes para las especies migratorias, particularmente para aquellas con hábitos arbóreos. Destacamos la importancia de evaluar la importancia de de los hábitas modificados particularmente en función de la composición de especies, y en función de las especies para las cuáles se desea evaluar la importancia de los hábitats modificados, en nuestro caso, para las especies típicas de bosque tropical.