Swimming in response to light by larvae of the tropical serpulid Spirobranchus giganteus

The planktotrophic trochophore of the serpulid polychaete Spirobranchus giganteus (Pallas) responds positively to visible light of wavelengths shorter than 590 nm. The response does not habituate, remaining effective for at least 2 h. The position and orientation of the 2-celled eyespot suggest that continuous forward movement occurs when the eyespot microvilli are shaded, a condition that could be caused by the pigment cell or by an outside shadow. Comparison with other larvae indicates interspecific differences in both light response and eyespot orientation. At the metatrochophore stage there is a loss of response to white light as well as changes in swimming speed and behaviour.     

Habitat selection predicts genetic relatedness in an alpine ungulate

Landscape heterogeneity plays an integral role in shaping ecological and evolutionary processes. Despite links between the two disciplines, ecologists and population geneticists have taken different approaches to evaluating habitat selection, animal movement, and gene flow across the landscape. Ecologists commonly use statistical models such as resource selection functions (RSFs) to identify habitat features disproportionately selected by animals, whereas population genetic approaches model genetic differentiation according to the distribution of habitat variables. We combined ecological and genetic approaches by using RSFs to predict genetic relatedness across a heterogeneous landscape. We constructed sex- and season-specific resistance surfaces based on RSFs estimated using data from 102 GPS (global positioning system) radio-collared mountain goats (Oreamnos americanus) in southeast Alaska, USA. Based on mountain goat ecology, we hypothesized that summer and male surfaces would be the best predictors of relatedness. All individuals were genotyped at 22 microsatellite loci, which we used to estimate genetic relatedness. Summer resistance surfaces derived from RSFs were the best predictors of genetic relatedness, and winter models the poorest. Mountain goats generally selected for areas close to escape terrain and with a high heat load (a metric related to vegetative productivity and snow depth), while avoiding valleys. Male- and female-specific surfaces were similar, except for winter, for which male habitat selection better predicted genetic relatedness. The null models of isolation-by-distance and barrier only outperformed the winter models. This study merges high-resolution individual locations through GPS telemetry and genetic data, that can be used to validate and parameterize landscape genetics models, and further elucidates the relationship between landscape heterogeneity and genetic differentiation.     

Habitat fragmentation lowers survival of a tropical forest bird.

Population ecology research has long been focused on linking environmental features with the viability of populations. The majority of this work has largely been carried out in temperate systems and, until recently, has examined the effects of habitat fragmentation on survival. In contrast, we looked at the effect of forest fragmentation on apparent survival of individuals of the White-ruffed Manakin (Corapipo altera) in southern Costa Rica. Survival and recapture rates were estimated using mark-recapture analyses, based on capture histories from 1993 to 2006. We sampled four forest patches ranging in size from 0.9 to 25 ha, and four sites in the larger 227-ha Las Cruces Biological Station Forest Reserve (LCBSFR). We found a significant difference in annual adult apparent survival rates for individuals marked and recaptured in forest fragments vs. individuals marked and recaptured in the larger LCBSFR. Contrary to our expectation, survival and recapture probabilities did not differ between male and female manakins. Also, there was no support for the existence of annual variation in survival within each study site. Our results suggest that forest fragmentation is likely having an effect on population dynamics for the White-ruffed Manakin in this landscape. Therefore, populations that appear to be persisting in fragmented landscapes might still be at risk of local extinction, and conservation action for tropical birds should be aimed at identifying and reducing sources of adult mortality. Future studies in fragmentation effects on reproductive success and survival, across broad geographical scales, will be needed before it is possible to achieve a clear understanding of the effects of habitat fragmentation on populations for both tropical and temperate regions.     

Habitat selection increases the isolating effect of habitat fragmentation on the gopher tortoise

Habitat selection requires choice, which differentiates it from habitat use, and choice, in turn, is dependent upon the responses of organisms to the environmental, social, and other cues that they perceive. Habitat selection by the gopher tortoise (Gopherus polyphemus) was investigated by translocating tortoises and monitoring their movements within two sites in central Florida. The first site supported a stable preponderance of high-quality habitat, and tortoises avoided areas with a dense tree canopy cover caused by fire exclusion. The second site was badly invaded by an introduced weed, and tortoises avoided areas where the weed had formed a dense monoculture. At both sites, individuals appeared to be responding to visual cues to avoid areas that were relatively dark. In landscapes with relatively large amounts of high-quality habitat, this avoidance behavior serves the gopher tortoise well by keeping individuals within the dominant habitat type. In degraded areas, high-quality habitat often becomes increasingly uncommon, and the avoidance behavior exhibited by the tortoises will result in individuals becoming confined to small patches, causing a significant reduction in fitness and hence questioning their long-term survival in such areas. The results from our study show that in order to maintain viable tortoise populations in areas increasingly subjected to human fragmentation and degradation, it is crucial not only to suppress tree canopy cover continually and prevent invasion by exotic weeds, but also to be mindful that the avoidance behavior of the gopher tortoise could prevent individuals from fully occupying a high-quality habitat in response to restoration and management efforts.     

Habitat selection models to account for seasonal persistence in radio telemetry data

Models for the analysis of habitat selection data incorporate covariates in an independent multinomial selections model (McCracken et al. 1998) Ramsey and Usner 2003 and an extension of that model to include a persistence parameter (2003). In both cases, all parameters are assumed to be fixed through time. Radio telemetry data collected for habitat selection studies typically consist of animal relocations through time, suggesting the need for an extension to these models. We use a Bayesian approach that allows for the habitat selection probabilities, persistence parameter, or both, to change with season. These extensions are particularly important when movement patterns are expected to differ seasonally and/or when availabilities of habitats change throughout the study period due to weather or migration. We implement and compare the models using radio telemetry data for westslope cutthroat trout in two streams in eastern Oregon.     

Habitat structure,population abundance and the opportunity for selection on body weight in the amphipodEogammarus oclairi

The importance of oyster-shell habitat-characteristics (depth of the shell layer or degree of fragmentation) to the amphipodEogammarus oclairi were studied in Grays Harbor estuary (Washington, USA) in regard to their effect on local density ofE. oclairi, the risk of predation by juvenile Dungeness crabsCancer magister, and the opportunity for selection on body weight during pairing.E. oclairi was the most abundant macrofaunal species in the intertidal oyster-shell assemblages (density range = 20 to 8500 amphipods m^–2), and its density was positively correlated with the depth of the oyster-shell layer (r = 0.85,n = 30,p < 0.005). Field experiments showed that amphipod density was much lower when oyster shells were whole (x = 340.7 ± 72.1,n = 10) as opposed to fragmented [x = 41.4 ± 9.3,n = 10;t _c (Welch's approximatet-test) = 13.0,df = 9.3,p < 0.05]. Densities of a predator, juvenileC. magister, were not affected by depth of the shell layer nor by degree of fragmentation (whole shell,x = 14.6 ± 13.0 crab;fragmented shell,x = 18.7 ± 2.4 crab;t _c = 0.83,df = 9.7,p > 0.05). Predation rate on single amphipods by crabs did not differ between habitat types (whole shells vs fragmented shells), but mating pairs were consumed more often in the whole-shell treatment (whole shell,x = 0.9 ± 0.8, fragmented shell,x = 0.1 ± 0.3). There were no differences in the size of single amphipods (both sexes) consumed between treatments, or in the size of the paired males consumed. Field experiments showed that the opportunity for selection (i) on male body weight increased with increasing amphipod density which, in turn, increased with increasing degree of shell fragmentation (whole-shell treatment,i = 0.0014 ± 0.0002, fragmented-shell treatment,i = 0.3756 ± 0.0338). Large spatial and temporal fluctuations in population abundance complicate the evaluation of the importance of selection in determining traits such as body weight.     

城市山斑鸠(Streptopelia orientalis)栖息地选择研究概况——以拉萨市为例

近年来,随着城市化的发展,野生动物栖息地的减少,使得城市中动物的种类和数量也急剧下降.山斑鸠作为城市鸟类动物多样性的重要组成部分,其栖息环境更需严格保护.通过拉萨市区的6个具有代表性地点对山斑鸠的栖息地选择进行了初步调查研究;用主成分分析(PCA)6个栖息地,最终得到6个地区的主成分综合得分排序表,山斑鸠对栖息地环境的...     

Habitat selection of two congeneric bivalves,Cardium edule and C. glaucum in sympatric and allopatric populations

Habitat selection of two bivalve species, Cardium edule (L.) and C. glaucum (Bruguière) is described for sympatric and allopatric populations of both sibling species. It is demonstrated that C. edule grows faster than C. glaucum and is absent from localities with periodic low food-availability. The ability to burrow of C. glaucum is low compared with that of C. edule; the former species does not occur in very loose, well-sorted sand near the coast. Earlier studies which suggest that tidal range determine the species distribution could not be confirmed.     

Determining Minimum Habitat Areas and Habitat Corridors for Cougars

I simulated population dynamics of cougars to predict the minimum areas and levels of immigration needed to avoid population extinction caused by demographic and environmental stochasticity for a period of 100 years. Under most plausible parameter values, the model predicted very low extinction risk in areas as small as 2200 km², and (in the absence of immigration) increasing risk as area decreased below 2200 km². If as few as one to four animals per decade could immigrate into a small population, the probability of population persistence increased markedly. Thus a corridor for immigration will benefit a small population in an area where further loss of habitat will occur. The model was applied to the cougar population in the Santa Ana Mountain Range of southern California (2070 km², with about 20 adults). Field data support the model’s conclusion that this population is demographically unstable. There will be a high risk of extinction if the habitat is reduced to currently protected and connected areas (1114 km²). A movement corridor allowing immigration from the adjacent population and intra-range corridors would greatly enhance the prognosis. However, the last corridor for immigration has been degraded by recent human activity. Within the mountain range, cougars recently became extinct in a 75 km² habitat fragment recently isolated by development, and cougars will become extinct in another 150 km² of habitat if a proposed housing project occludes a critical corridor. Radio tracking has confirmed use of this and other important corridors. Neither the model nor the field data alone would have much influence in the face of development pressure; together they have stimulated interest in restoring and protecting critical corridors in this range. Nonetheless, the long-term prognosis for this populations is bleak, because 22 local governments review potential impact on a case-by-case basis. Effective land-use planning must be spatially explicit and regional in scope. Because cougars need corridors and because telemetered cougars can quickly identify movement corridors, cougar research is an efficient and appropriate way to inject biological data into such planning efforts.     

Habitat Loss and Changes in the Species-Area Relationship

Abstract: The species-area relationship (SAR) has been used successfully to predict extinction from extent of habitat reduction. These extinction estimates assume that species have uniformly distributed range requirements and a minimum abundance level required for persistence; how many species are lost depends solely on how much habitat is removed, not on where it is removed. We consider another limiting case in which range requirements, rather than abundances, determine extinctions. We used a new method for constructing SARs based on assumptions about geographic ranges of species. Our results show that habitat destruction can change the SAR and consequently the number of species predicted to be lost due to habitat destruction. Our method generates SARs that vary in shape according to the specific distributions of geographic range and occupancy but that have the common feature of being described by a power law with an exponent of <1. When the geographic range of species was included in the SAR, the way habitat was lost became important. Although the SAR before habitat destruction is often used to predict species loss after habitat destruction, assumptions must be clearly stated. To predict the damage caused by habitat loss with our model, it is necessary to know the fraction of aggregated species, the distribution of geographic ranges, the form of habitat destruction, and the sampling protocol. The remaining theoretical challenge is to develop a full theory that links abundance and range.     

Habitat choice in the intertidal snail Tegula funebralis

Intraspecific variation in habitat preference was studied in the black turban snail Tegula funebralis (Adams, 1854), at two locations on the northern U.S. Pacific Coast. Studies in 1977 using a mass-marking technique showed that most snails found either above or in permanent tidepools at low tide return to their original habitats within a few days after experimental habitat reversal. This return is not due to homing behavior, but is apparently based on the recognition of ecological characteristics of the two habitats. Experiments in 1978 with individually-marked snails suggest that they prefer specific intertidal levels, and not merely above-pool or in-pool habitats. Theoretical models predict that this behavior could play a major role in the maintenance of genetic polymorphism in a species like T. funebralis, whose intertidal environment is characterized by extreme spatial heterogeneity.     

Mitigation of Habitat "Take": Application to Habitat Conservation Planning

One of the most important provisions of the U.S. Endangered Species Act precludes the "taking" of listed species on both public and private land. In past Endangered Species Act litigation, take has been broadly interpreted to include the destruction or modification of habitats as well as the direct killing of animals. This requirement created an extensive burden on private landowners to provide habitats for listed species. This burden was substantially lessened when the ESA was modified in 1982 to allow incidental takings conditioned on preparation of a satisfactory "habitat conservation plan." Because the majority of listed species are imperiled due to habitat modification, most habitat conservation plans must demonstrate defensible methods to mitigate against incidental habitat loss. A review of HCPs for the Northern Spotted Owl ( Strix occidentalis), and other species, indicates that mitigation solutions are often arbitrary, lacking an empirical foundation in the species' life history requirements. Based on data from the Spotted Owl, we illustrate a biologically based method for estimating the areal requirements necessary to mitigate against the take of essential habitats. Toward this goal we adopt the concept of "core area," that portion of an animal's home range that receives disproportionate use. We estimated core areas by means of the adaptive kernel density function and tested against a null distribution of animal use that assumes a bivariate, uniform distribution of locations within the home range. The method we illustrate, which is defensible, repeatable, and empirical, is a clear improvement over the ad hoc methods used in many habitat conservation plans. Further, the methods we propose should be applicable to a large number of terrestrial species for which home range is a meaningful concept.     

Habitat selection in a coastal dolphin species (<Emphasis Type="Italic">Cephalorhynchus hectori</Emphasis>)

Hector's dolphin ( Cephalorhynchus hectori) is a small New Zealand delphinid with a coastal distribution. Within a strip of 1 km from shore, the present study quantified the habitat used by the dolphins ( n=461 groups) over a 19-month period (216 field days with 966 survey hours) by recording the abiotic factors sea surface temperature (SST), water depth and water clarity. Resource selection functions were used to distinguish the properties of 461 "used" sites (dolphins present) from 425 "unused" sites (no dolphins present) in six different study areas. Most dolphins were encountered in waters <39 m depth, with <4 m Secchi disk visibility and >14°C temperature. The preference of Hector's dolphins for warm and turbid waters was tested using eight models. Water depth, water clarity, SST and the study area explained dolphin presence to a very significant degree ( p<0.001), and the model allowed the creation of probability plots for a variety of combinations of the variables. Habitat selection by dolphins differed between study areas, particularly between east and west coasts, in summer (December–February) and winter (June–August). Dolphin abundance appeared to change seasonally in some study areas, possibly due to a more offshore distribution of their prey in the winter, with its lower SSTs. This was so especially in summer (the main reproductive season), when dolphins (frequently with calves) occupied shallow and turbid waters, whereas in winter less use was made of this habitat.     

Habitat saturation drives thresholds in stream subsidies

Understanding how abundance regulates the effects of organisms on their ecosystems remains a critical goal of ecology, especially for understanding inter-ecosystem transfers of energy and nutrients. Here we examined how territoriality and nest-digging by anadromous salmon mediate trophic subsidies to stream fishes. Salmon eggs become available for consumption primarily by the digging of salmon that superimpose their nests on previous nests. An individual-based model of spawning salmon predicted that territoriality and habitat saturation produce a nonlinear effect of salmon density on numbers of available eggs to resident predators. Field studies in Alaskan streams found that higher densities of salmon produce disproportionately more eggs in stream drift and in diets of resident fishes (Arctic grayling and rainbow trout). Bioenergetics model simulations indicated that these subsidies produce substantially enhanced growth rates of trout. These results demonstrate that small changes in salmon abundance can drive large changes in subsidies to stream food webs. Thus, the ecological consequences of population declines of keystone species, such as salmon, will be exacerbated when behavior generates nonlinear impacts.     

Habitat Use and Life History as Predictors of Bird Responses to Habitat Change

Abstract:  In theory the consideration of life-history characteristics should provide a way of making predictive generalizations about the responses of different species to environmental modification. Nevertheless, few studies have tested the validity of this assumption or attempted to apply it across large numbers of related species. We explored both quantitative and qualitative contrasts between species of waterbirds that have either expanded or contracted their ranges in southern Africa over the past 40 years to test the hypothesis that expansionists and contractionists, respectively, should share life-history characteristics and/or ecological attributes. Similarities and differences in life history and ecology were explored through multivariate statistics. Overall, life-history traits provided an inadequate explanation of whether species would be range expansionists or contractionists. By contrast, ecological attributes of species that related to habitat use correlated well with range changes. In particular, waterbird species that inhabit pans seemed to be preadapted to using human-made dams and impoundments. The ability of many species to use artificial wetlands has aided their westward range expansions into arid regions of southern Africa. By contrast, species that rely on vegetated wetlands and that require reeds for nesting were predisposed to range contraction because their habitats have been severely affected by agricultural development and urbanization. In direct contrast to range expansions, most range contractions were west to east, the eastward contraction reflected the high level of wetland loss and degradation in the eastern lowlands of South Africa. Based on analysis of ecological attributes of regional contractionists, several additional species were identified as of potential conservation concern, although such concern may not as yet have been expressed.