Spatial scaling of allometry for terrestrial,mammalian carnivores

A regression slope of –0.75 between log₁₀ density and log₁₀ body mass is thought to express equivalence of energy conversion among species' populations of similar taxonomic and trophic status. Using larger sample sizes than the usual 1–3 density estimates per species, we estimated a regression slope of –0.71 for terrestrial mammalian carnivores. We investigated the sampling variation in this estimate, and those derived from smaller intra-specific subsets, using 1000-iteration bootstrap analyses to obtain 90% confidence intervals. As expected, these widened as random subsets were reduced in size, but always contained the postulated –0.75. However, log₁₀ density also declined as 3/4 of the log₁₀ spatial extent of study area, and study area accounted for virtually all of the variation in density that was previously thought due to body mass. We removed the effect of study area by using the species-specific regression models between density and study area to predict density at a common scale of 400 km². These common-scale densities regressed against body mass with a slope of –0.16, but separated into body mass classes less than and greater than 11 kg, they produced slopes that were not significantly different from zero. We show that the allometry of density could be a case of circular logic, whereby body mass has influenced the investigator's choice of study area, and the resulting scale-dependent densities are related back to body mass. To test the allometry hypothesis, the effect of study area on density estimates needs to be removed. This requires conducting larger-scale studies of the smaller-bodied species so that all species compared are represented by an average study area that is near the common scale. Furthermore, study sites need to be selected and designed to represent more than the local detail in species' density.     

Spatial Variation of Bird Species in Landscapes Dominated by Old-growth Forests in Northern Boreal Finland

An important issue in conservation planning is to study the distribution and abundance patterns of species in natural landscapes. Information of concordant and clumped species distribution pattertns can enhance attempts to focus conservation efforts in sites/areas preferred by various species. We compared bird species abundance, community composition and species distribution patterns in three large old-growth forest areas (size 40–120 km²) in northern boreal Finland on the basis of quantitative bird censuses. Total bird density and species composition, and mean density and variances of the most abundant species were highly similar between the three areas. Most of the bird species were distributed randomly within the areas and species preferring old-growth forests showed compensatory density variation without preference for any sub-area. Mean density of species preferring old-growth forests was significantly higher in the studied large old-growth forests than in smaller old-growth forests and was about threefold higher than regional density of species in a predominantly managed landscape matrix. Bird species preferring old-growth forests are probably not dependent on a certain specific part of a virgin boreal forest landscape but rather on the overall size of the high-quality and diverse old-growth forest area.     

Estimating population size by spatially explicit capture–recapture

The number of animals in a population is conventionally estimated by capture–recapture without modelling the spatial relationships between animals and detectors. Problems arise with non‐spatial estimators when individuals differ in their exposure to traps or the target population is poorly defined. Spatially explicit capture–recapture (SECR) methods devised recently to estimate population density largely avoid these problems. Some applications require estimates of population size rather than density, and population size in a defined area may be obtained as a derived parameter from SECR models. While this use of SECR has potential benefits over conventional capture–recapture, including reduced bias, it is unfamiliar to field biologists and no study has examined the precision and robustness of the estimates. We used simulation to compare the performance of SECR and conventional estimators of population size with respect to bias and confidence interval coverage for several spatial scenarios. Three possible estimators for the sampling variance of realised population size all performed well. The precision of SECR estimates was nearly the same as that of the null‐model conventional population estimator. SECR estimates of population size were nearly unbiased (relative bias 0–10%) in all scenarios, including surveys in randomly generated patchy landscapes. Confidence interval coverage was near the nominal level. We used SECR to estimate the population of a species of skink Oligosoma infrapunctatum from pitfall trapping. The estimated number in the area bounded by the outermost traps differed little between a homogeneous density model and models with a quadratic trend in density or a habitat effect on density, despite evidence that the latter models fitted better. Extrapolation of trend models to a larger plot may be misleading. To avoid extrapolation, a large region of interest should be sampled throughout, either with one continuous trapping grid or with clusters of traps dispersed widely according to a probability‐based and spatially representative sampling design.     

Can occupancy patterns be used to predict distributions in widely separated geographic regions?

Occupancy models, that describe the presence and absence patterns of a species in a given area, are increasingly being used to predict the occurrence of the species in unsurveyed sites, as an aid to conservation planning. In this paper, we consider whether conclusions about local distributions derived from one landscape can be extrapolated to others. We found that habitat patchiness influenced the distribution and abundance of the host-specific moth Wheeleria spilodactylus in a similar way in two landscapes widely separated geographically. In both geographic regions, the spatial location (positive effect of connectivity), and quantity of resource (positive effect of host plant density) increased the likelihood that the moth would be present, consistent with the expectations of metapopulation dynamics. Though some biological attributes of the species appeared to be slightly different, including population density and the timing of the life cycle (phenology), occupancy patterns in one landscape accurately predict occupancy in the other landscape. Our results suggest that it maybe possible to make predictions from one landscape to another, even when the landscapes are widely separated.     

Landscape scale variation in the hydrologic niche of California coast redwood

Topoclimatic diversity within forest landscapes can underlie variation in water availability, which may correspond to patterns in habitat suitability of tree species with differing hydrologic niches. However, the trade-off between the collection of data at a fine grain size over large spatial extents has limited comprehensive analyses of landscape scale variation in habitat suitability. We present a fine scale analysis of the roles of topographic gradients in moisture availability, soil water storage and fog frequency in the spatial pattern of habitat suitability for coast redwood Sequoia sempervirens, at 10 m resolution across 34 800 ha and three landscapes spanning approximately one-third of redwood's latitudinal range. A new 10 m resolution presence-absence map derived from airborne imaging spectroscopy was used to characterize current redwood distributions in three landscapes. Access to belowground moisture was assessed through four measures calculated from a high-resolution LiDAR digital elevation model, soil water storage was mapped from the USDA Soil Survey Geographic Database, and fog frequency was calculated from MODIS cloud cover data. Access to belowground moisture and fog predicted variation in suitability as redwood habitat from 22–75% and predicted redwood presence and absence at 10 m resolution with 63–74% accuracy. Across all three landscapes, redwood density consistently decreased with increasing interpolated height above a stream (IHAS), but the role of other predictors varied among the sites. Our results challenge previous assumptions that redwood habitat suitability within much coarser resolutions (800 m × 800 m) can be described by a single value. The elevated habitat suitability of sites close to streams suggests that these sites should be evaluated for their potential to become microrefugia within landscapes that may become climatically-unsuitable for redwoods at a regional scale.     

A test of Brown's principle in the intertidal limpet Collisella scabra (Gould, 1846)

Aim Brown's principle predicts that a species will peak in density near its range centre, and decline gradually towards the margins of its geographical distribution. The decline is assumed to reflect a decrease in individual performance near range margins. I test this abundance–performance hypothesis by comparing patterns in density and size across the northern half of the geographical distribution of the marine patellogastropod Collisella scabra (Gould, 1846). Location Collisella scabra is a high intertidal patellogastropod species distributed along the Pacific coast of North America from Cape Mendocino (CA, USA) to southern Baja California (Mexico). I surveyed 11 research sites spanning c. 36–44° N. Methods In each of the 11 research sites I surveyed four distinct microhabitats, and compared spatial patterns in density and in the size of solitary limpets. Results Both density and size were highly variable across the species range. Density peaked near the northern range margin, and showed greater variance at small spatial scales (< 10 km) than at large scales (> 100 km). In contrast, large size occurred uniformly across the survey area, and size was strongly associated with microhabitat. Main conclusion Collisella scabra does not show spatial patterns of density or performance that are consistent with Brown's principle. The underlying assumptions of Brown's principle may conflict with specific characteristics of C. scabra's life history and/or patterns of environmental variation across its range. Because such conflicts may be common in a large number of marine and terrestrial species, the generality of Brown's principle is questioned.     

Mammal population densities at a global scale are higher in human‐modified areas

Global landscapes are changing due to human activities with consequences for both biodiversity and ecosystems. For single species, terrestrial mammal population densities have shown mixed responses to human pressure, with both increasing and decreasing densities reported in the literature. How the impacts of human activities on mammal populations translates into altered global density patterns remains unclear. Here we aim to disentangle the effect of human impacts on large‐scale patterns of mammal population densities using a global dataset of 6729 population density estimates for 468 mammal species (representing 59% and 44% of mammalian orders and families). We fitted a mixed effect model to explain the variation in density based on a 1‐degree resolution as a function of the human footprint index (HFI), a global proxy of direct and indirect human disturbances, while accounting for body mass, trophic level and primary productivity (normalized vegetation index; NDVI). We found a significant positive relationship between population density and HFI, where population densities were higher in areas with a higher HFI (e.g. agricultural or suburban areas – no populations were located in very high HFI urban areas) compared to areas with a low HFI (e.g. wilderness areas). We also tested the effect of the individual components of the HFI and still found a consistent positive effect. The relationships remained positive even across populations of the same species, although variability among species was high. Our results indicate shifts in mammal population densities in human modified landscapes, which is due to the combined effect of species filtering, increased resources and a possible reduction in competition and predation. Our study provides further evidence that macroecological patterns are being altered by human activities, where some species will benefit from these activities, while others will be negatively impacted or even extirpated.     

Participatory wildlife surveys in communal lands: a case study from Simanjiro,Tanzania

It is widely accepted that protected areas alone are not sufficient to conserve wildlife populations particularly for migratory or wide‐ranging species. In this study, we assess the population density of migratory species in the Tarangire–Simanjiro Ecosystem by conducting a ground census using DISTANCE sampling. We focus on the Simanjiro Plains which are used as a dispersal area by wildebeest (Connochaetes taurinus) and zebra (Equus burchellii). We demonstrate that DISTANCE sampling can provide precise estimates of population density and is an affordable method for monitoring wildlife populations over time. We stress the importance of involving local communities in monitoring programmes across landscapes that incorporate communal lands as well as protected areas.     

Spatial distribution and settlement strategies in willow ptarmigan

In heterogeneous landscapes individuals select among several habitat patches. The fitness rewards of these choices are assumed to play an important role in the distribution of individuals across landscapes. Individuals can either use environmental cues to directly assess the quality of breeding sites, or rely on social cues to guide the settlement decision. We estimated the density of adult birds and per capita reproductive success of willow ptarmigan over 5–15 years in 42 survey areas, nested within 5 spatially separated populations in south-central Norway. Our aims were to (1) examine spatial and temporal patterns of variation in densities of adult birds (i.e., the breeding densities) and reproductive success (juveniles/pair) measured in autumn and (2) evaluate which habitat distribution model best described the distribution of willow ptarmigan across heterogeneous mountain landscapes. Variation in density of adult birds was primarily attributable to variation between survey areas which could arise from spatial heterogeneity in adult survival or as a consequence of spacing behavior of juveniles during the settlement stage. In contrast, reproductive success was more variable between years and did not vary consistently between survey areas once year effects were accounted for. The lack of any relationship between the density of adult birds and reproductive success supported the predictions of an ideal free distribution (IFD), implying that within years, the mean reproductive success was approximately equal across survey areas. However, analysis based on Taylor's power law (i.e., the relationship between logarithms of spatial variance and mean density of adult birds) suggested that aggregation was stronger than expected under IFD. This implies that the relative change in density of adult birds was larger in areas with high mean densities than in areas with low densities. The exact mechanisms causing this statistical pattern are unclear, but based on the breeding biology of willow ptarmigan we suggest that yearlings are attracted to areas of high densities during the settlement period in spring. Our study was conducted during a period of low overall density and we suggest that this pattern might be particular to such situations. This implies that the presence of conspecifics might represent a cue signaling high adult survival and thus high habitat quality.     

Potential decoupling of trends in distribution area and population size of species with climate change

Global climates are changing rapidly and biological responses are becoming increasingly apparent. Here, we use empirical abundance patterns across an altitudinal gradient and predicted altitudinal range shifts to estimate change in total population size relative to distribution area in response to climate warming. Adopting this approach we predict that, for nine out of 12 species of regionally endemic birds, total population size will decline more rapidly than distribution area with increasing temperature. Two species showed comparable loss and one species exhibited a slower decline in population size with change in distribution area. Population size change relative to distribution area was greatest for those species that occurred at highest density in the middle of the gradient. The disproportional loss in population size reported here suggests that extinction risk associated with climate change can be more severe than that expected from decline in distribution area alone. Therefore, if we are to make accurate predictions of the impacts of climate change on the conservation status of individual species, it is crucial that we consider the spatial patterns of abundance within the distribution and not just the overall range of the species.     

Estimated density of four carabid beetle species in Mongolian oak and Korean red pine forest ecosystems on Baekdudaegan mountain range (Mt. Oade and Mt. Guryong) of South Korea

The estimation of animal population size is a primary field of interest for wildlife biologists, and such numerical estimation of wild animals is a very important factor in establishing national policy towards nature. Therefore, we performed this study to estimate the population density of carabid beetles preying on soil biota at the Mongolian oak (Quercus mongolica) forests and Korean red pine (Pinus densiflora) forests of two mountains, Mt. Odae and Mt. Guryong. We used the trapping web method with pitfall traps to collect the beetles. We calculated the estimated density of a total of four carabid beetle species in two specific regions and converted them to an estimated beetle population size within a certain area by using the study area. From our estimates, one beetle species, Leptocarabus seishinensis seishinensis L., displayed statistically significant results. Although there was no appreciable difference in the makeup of different carabid beetle species between the two forest communities, the population size of the beetle species was larger in Mongolian oak forests than in Korean red pine forests. The spatial distribution of carabid beetles by forest type did not show any preference for particular spots. Our results showed that carabid beetles did not have specific home ranges and that they were not density dependent. We expect to use the raw data to recognize the response of soil organisms to changes in the habitat environment and to track the patterns of change more accurately over long passages of time.     

Lemurs in a complex landscape: mapping species density in subtropical dry forests of southwestern Madagascar using data at multiple levels

The study of southern dry forest lemurs has been largely restricted to small reserves; yet, the majority of the region's lemur populations reside outside protected areas. Lemur catta and Propithecus verreauxi occupy the same forests but have different dietary preferences. This study assessed L. catta and P. verreauxi population densities across a 3-km dry forest gradient (1,539?ha) in southern Madagascar. The study was designed to allow lemur densities to be related to particular forest types. A particular aim of this study was to collect lemur data in both protected and unprotected areas. Density estimates were calculated using point transect distance sampling in a study area that contained the Beza Mahafaly Special Reserve and the adjacent disturbed forests. The highest densities recorded for each species were in the protected area where the two species were most segregated in their distribution, with L. catta density highest in gallery forest type and P. verreauxi density highest in dry deciduous. Densities of both species varied widely outside the protected area, but P. verreauxi density was more uniform than was L. catta. Results of this study indicate that patterns of lemur density in protected areas are not representative of patterns in disturbed forests; this also suggests that we cannot fully understand the ecological constraints facing primate species by studying them only in protected areas. This research highlights the value of pairing the study of landscape-level patterns of species distribution with both local ground-level ecological interpretations and broad-scale satellite data; information from only one level may give an incomplete view of the community.     

The influence of increasing population size and vegetation productivity on elephant distribution in the Kruger National Park

Decisions to reduce the impacts of large herbivores on biodiversity in protected areas are often based on controlling their numbers. However, numbers per se may not be the foremost consideration when managing impacts. This is because density‐related changes in distribution can also affect habitat utilization and hence, impact. In this study we tested whether changes in the distribution of African elephants are associated with increasing population size. We used spatially explicit count data collected during the dry seasons from 1998 to 2004 in South Africa's Kruger National Park. We did this at five spatial scales and in landscapes defined by vegetation, geology, climate and soils. We then investigated whether observed distributions and grid‐cell‐specific densities were associated with the remotely sensed Normalized Difference Vegetation Index (NDVI) as a measure of productivity and therefore food resource availability at the landscape scale. Consistent with density mediated changes, we found that elephant grid‐cell occupancy increased with population size, while grid‐cell‐specific density became less variable. In addition, the combined distribution of bull groups and breeding herds became less clumped with increasing population size. We further found that within landscapes elephants were present on grid‐cells with higher NDVI values, but that the influence of NDVI during the dry season on densities among landscapes may be weak. These results suggest that NDVI was more indicative of structural habitat choices such as woody vegetation than food availability per se. Our study highlights the need to consider factors other than population size alone when formulating management decisions to reduce large herbivore impacts on biodiversity in protected areas.     

Metapopulation dynamics of a beetle species confined to burned forest sites in a managed forest region

Despite increasing awareness of the theoretical importance of habitat dynamics on metapopulations, only a few empirical studies have been conducted. We aimed to increase our understanding of how patch size, dynamics and connectivity affect colonization–extinction dynamics and the occurrence patterns of a beetle (Stephanopachys linearis), which breeds only in burned trees, existing as dynamic habitat patches that have become rare in managed forest landscapes. We assessed species’ presence/absence twice in all known habitat patches (i.e. > 1 ha sites where forest fires had occurred during the previous 2–15 yr) in a 200 × 150 km region of central Sweden, dominated by managed boreal forest. Evaluated over six years, the colonization rate was 47% and the local extinction risk was 65%. Probability of colonization increased with patch size (number of suitable trees in a site) and connectivity to occupied patches within 30 km, and decreased with increasing time since fire. Local extinction risk decreased with habitat patch size but increased, unexpectedly, with connectivity. Occurrence increased with patch size and decreased with increasing time since fire. At a regional scale, S. linearis tracks the fire dynamics by colonising sites with burned trees and by becoming extinct at rates which make the species rare at sites where burnt trees are more than eight years old. In managed boreal forest landscapes, a large proportion of sites may be created by prescribed burning (in our study area: 82%), and consequently human decisions strongly affect the future amount of habitat for fire‐dependent species and its spatial distribution. Stephanopachys linearis uses burned sites more often if more trees are retained and, to some extent, if sites are concentrated in those parts of a region that already support high population densities of the species.     

Nest Suitability,Fine-Scale Population Structure and Male-Mediated Dispersal of a Solitary Ground Nesting Bee in an Urban Landscape

Bees are the primary pollinators of flowering plants in almost all ecosystems. Worldwide declines in bee populations have raised awareness about the importance of their ecological role in maintaining ecosystem functioning. The naturally strong philopatric behavior that some bee species show can be detrimental to population viability through increased probability of inbreeding. Furthermore, bee populations found in human-altered landscapes, such as urban areas, can experience lower levels of gene flow and effective population sizes, increasing potential for inbreeding depression in wild bee populations. In this study, we investigated the fine-scale population structure of the solitary bee Colletes inaequalis in an urbanized landscape. First, we developed a predictive spatial model to detect suitable nesting habitat for this ground nesting bee and to inform our field search for nests. We genotyped 18 microsatellites in 548 female individuals collected from nest aggregations throughout the study area. Genetic relatedness estimates revealed that genetic similarity among individuals was slightly greater within nest aggregations than among randomly chosen individuals. However, genetic structure among nest aggregations was low (Nei’s G_ST = 0.011). Reconstruction of parental genotypes revealed greater genetic relatedness among females than among males within nest aggregations, suggesting male-mediated dispersal as a potentially important mechanism of population connectivity and inbreeding avoidance. Size of nesting patch was positively correlated with effective population size, but not with other estimators of genetic diversity. We detected a positive trend between geographic distance and genetic differentiation between nest aggregations. Our landscape genetic models suggest that increased urbanization is likely associated with higher levels of inbreeding. Overall, these findings emphasize the importance of density and distribution of suitable nesting patches for enhancing bee population abundance and connectivity in human dominated habitats and highlights the critical contribution of landscape genetic studies for enhanced conservation and management of native pollinators.     

Bird diversity and distribution in mosaic landscapes around Jammu,Jammu & Kashmir

The composition and persistence of avian population depends not only on the size and structure of habitat patch but also on surrounding landscapes which contribute to many environmental functions in an urban environment. To assess the bird assemblages around an urban conglomeration, we surveyed the urban landscape of Jammu stratified into six habitat types from January 2017 to December 2017. These comprised two aquatic (Nikki Tawi & Gharana Wetland Conservation Reserve), three terrestrial (Ramnagar Wildlife Sanctuary, Bahu-Mahamaya Forest & Jammu University Campus) and a mixed ecosystem, the Southern Open plains. Two hundred and eight species of birds in 63 families and 16 orders were recorded during the investigations. We observed that the protected ecosystems and semi disturbed landscapes harbored rich avian diversity among other sites. A distinct species overlap was noticed in all the study sites while the protected areas shared maximum similarity. The study indicated a defined set of bird assemblages for different habitats across the study area. More datasets are however required to understand the patterns and drivers of bird biodiversity in relation to the fast-expanding urbanization.     

马鞍列岛岩礁生境鱼类群落结构时空格局

基于2009年马鞍列岛潮下带岩礁生境的多网目三层组合刺网逐月调查数据,对鱼类群落月相和季度间的变化、区域尺度上的空间差异和群落的稳态进行了探讨,应用优势种相对丰度和生物量、定居性鱼类和洄游种的季节动态、非度量多维标度(nMDS)和生物量丰度曲线(ABC)分析方法对群落时空格局进行了分析。结果显示:季节性洄游种集中出现在夏秋季,但对岩礁生境的利用表现出不同区域的强度差异;小黄鱼Larimichthys polyactis和黄姑鱼Nibea albiflora周年利用岩礁生境,但强度有别,尤其在冬季;定居性鱼类褐菖鲉Sebastiscus marmoratus、斑头鱼Agrammus agrammus和大泷六线鱼Hexagrammos otakii在春末夏初的种群密度最高,同样表现出某些或大部分月份的区域差异;而河口种中国花鲈Lateolabrax maculatus则更多地选择秋冬季出现在岩礁生境。多元分析结果揭示了当地岩礁生境鱼类群落格局上显著的季节和区域差异,这是定居性鱼类对岩礁生境利用的阶段性变化和区域差异、结合洄游种季节迁移和选择性分布等因素作用下共同形成的格局。ABC分析进一步发现,丰富的鱼类生态类型形成了夏季岩礁生境更为稳定的群落状态,而冬季相反;同时各季度A区的群落干扰明显强过B区。研究表明,产卵季节海域西北部的岩礁生境很可能起着主要的产卵场功能,而东南部区域各季度皆侧重于幼鱼育肥场的功能表达。丰富的种类区系加之优势种的季节性交替出现,共同塑造了岩礁生境极具动态的鱼类群落格局,对维持岛礁海域鱼类多样性以及局部区域生态系统的稳定性起着非常重要的作用。     

Spatial and temporal variation in a suite of life-history traits in two species of wolf spider

Abstract.  1. Life-history traits and density were assayed in seven populations of two sympatric species of wolf spider for three consecutive years. The goal of the study was to quantify population dynamics and its relation to spatial and temporal life-history variation.
2. Adult female body size and fecundity varied significantly, among field sites and among years, in both species. Female spiders of both species differed in mean relative reproductive effort among sites, but not among years. The size of offspring was invariable, with no significant differences due to site or year.
3. All populations of both species tended to either decrease or increase in density during a given year and this was tightly correlated with changes in prey consumption rates.
4. Since life-history patterns are determined primarily by selection, it is concluded that size at sexual maturity for females is phenotypically plastic and responds to changes in prey availability. Offspring size however is not plastic and it is likely that other selection forces have determined offspring size. Temporal fluctuations in population size are correlated over a large area relative to dispersal capabilities for these species and conservation efforts for invertebrates must take this into consideration.