Predicting species interactions from edge responses: mongoose predation on hawksbill sea turtle nests in fragmented beach habitat

Because species respond differently to habitat boundaries and spatial overlap affects encounter rates, edge responses should be strong determinants of spatial patterns of species interactions. In the Caribbean, mongooses (Herpestes javanicus) prey on hawksbill sea turtle (Eretmochelys imbricata) eggs. Turtles nest in both open sand and vegetation patches, with a peak in nest abundance near the boundary between the two microhabitats; mongooses rarely leave vegetation. Using both artificial nests and hawksbill nesting data, we examined how the edge responses of these species predict the spatial patterns of nest mortality. Predation risk was strongly related to mongoose abundance but was not affected by nest density or habitat type. The product of predator and prey edge response functions accurately described the observed pattern of total prey mortality. Hawksbill preference for vegetation edge becomes an ecological trap in the presence of mongooses. This is the first study to predict patterns of predation directly from continuous edge response functions of interacting species, establishing a link between models of edge response and species interactions.     

Factors determining nest-site selection of surface-nesting seabirds: a case study on the world's largest pelagic bird,the Wandering Albatross (Diomedea exulans)

Several factors may drive bird nest-site selection, including predation risk, resource availability, weather conditions and interaction with other individuals. Understanding the drivers affecting where birds nest is important for conservation planning, especially where environmental change may alter the distribution of suitable nest-sites. This study investigates which environmental variables affect nest-site selection by the Wandering Albatross Diomedea exulans, the world's largest pelagic bird. Here, wind characteristics are quantitatively investigated as a driver of nest-site selection in surface-nesting birds, in addition to several topographical variables, vegetation and geological characteristics. Nest locations from three different breeding seasons on sub-Antarctic Marion Island were modelled to assess which environmental factors affect nest-site selection. Elevation was the most important determinant of nest-site selection, with Wandering Albatrosses only nesting at low elevations. Distance from the coast and terrain roughness were also important predictors, with nests more generally found close to the coast and in flatter terrain, followed by wind velocity, which showed a hump-shaped relationship with the probability of nest occurrence. Nests occurred more frequently on coastal vegetation types, and were absent from polar desert vegetation (generally above c. 500 m elevation). Of the variables that influence Wandering Albatross nest location, both vegetation type and wind characteristics are likely to be influenced by climate change, and have already changed over the last 50 years. As a result, the availability of suitable nest-sites needs to be considered in light of future climate change, in addition to the impacts that these changes will have on foraging patterns and prey distribution. More broadly, these results provide insights into how a wide range of environmental variables, including wind, can affect nest-site selection of surface-nesting seabirds.     

Factors affecting habitat selection in a specialist fossorial skink

Habitat specialists maximize their fitness by using a subset of the habitats that are potentially available to them and fare poorly if they move elsewhere. The factors that constrain habitat use are diverse and often difficult to identify, but are important to distinguish if we are to understand the trade-offs that drive species to become specialists. In the present study, we investigated habitat use in a fossorial skink, Lerista labialis , and explore the factors that confine it to the crests of sand dunes in the Simpson Desert, central Australia. Models positing that L. labialis selects dune crests because of their sparse cover of vegetation, more favourable temperatures, and greater abundance of preferred prey, received no support. Instead, a model positing that dune crests provide soft and less compacted sand that facilitates movement by L. labialis , was strongly supported. Sand on the crests was consistently softer that that on the sides and swales of the dunes; the skinks preferred soft rather than hard sand for movement in captivity, and were captured more often on experimentally softened sand than on compacted sand in the field. There was no evidence that L. labialis responds to attributes of the substrate other than softness because captive animals used loose sand from the dune crests, sides, and swales equally. We suggest that the dune crest environment allows L. labialis to reduce the energetic costs of locomotion, provides priority of access to the subterranean galleries of its termite prey, and also a secure refuge from surface-active predators and extreme surface temperatures.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 531–544.     

On a log-linear approach to detecting ecological interactions in monitored populations

We discuss a log-linear model for series of regular bird counts taken at a number of survey sites. The model is parameterized in terms of annual growth rates rather than actual indices of abundance, as is more frequently done. This not only permits easy estimation of and inference about these rates, but also allows us to model the effects upon population growth of covariates, such as the local presence of a competitor or predator, which may themselves vary in space and over time. A recursive relationship permits the expected count at a site to be functionally dependent upon the expected count at the previous visit. We discuss the advantages of using this relationship, rather than replacing the latter with their observed counterparts, as has been used previously.     

The habitat hectares approach to vegetation assessment: An evaluation and suggestions for improvement

Summary The habitat hectares approach is an explicit, quantitative method for assessing the quality of vegetation by adding scores that are assigned to 10 habitat attributes. We believe it will be more repeatable and transparent than other methods that rely on subjective judgement. However, we have four principal criticisms of the method as it is currently proposed: (i) measurement of some of the attributes may be subject to considerable error that varies among assessors; (ii) the comparison of each measure with a single benchmark does not accommodate appropriate disturbance regimes; (iii) the proposed combination of attributes leads to some apparent internal inconsistencies; and (iv) it is not clear how the method will actually be used in practice. We suggest modifications to address these concerns and improve the proposed method. Finally, we make additional suggestions about the method's potential application, including: separate reporting of the extent and quality of different vegetation types to avoid the inappropriate combination of measures of area and quality; valuing appropriate disturbance regimes in natural areas; and considering very carefully the application of compensation or mitigation measures.     

Distribution of badger latrines in a high-density population: habitat selection and implications for the transmission of bovine tuberculosis to cattle

Eurasian badgers Meles meles habitually deposit droppings and other scent marks at latrines, which may be associated with territorial defence, and communicate information related to group and individual identity and status, and food resources. Understanding patterns of latrine distribution contributes to our understanding of badger social behaviour, and may be relevant to managing the risks of transmission of bovine tuberculosis from badgers to cattle. We investigated the distribution of badger latrines relative to habitat composition in a high-density badger population occupying a 7 km² area of diverse landscape in south-west England. Results indicated that the frequency and density of badger latrines varied according to land use, with woodland and linear landscape features (particularly hedges and stone walls) being positively selected. The number of latrines decreased significantly with distance from linear features. Grassland was negatively selected given its availability, but contained the highest number of latrines. The tendency for latrines to be associated with particular habitat types covaried spatially across the study area. We present a habitat selection probability function, based on the output of our analyses, to allow comparison of observed versus expected latrine counts per habitat type at different sites. Habitat manipulation on farmland may offer opportunities to manage exposure of cattle to badger latrines. However, our analyses indicate that other factors (perhaps demographic or environmental) may also exert a substantial local influence on latrine location.     

Relationship among settling,demography and habitat selection: an approach and a case study

Summary We explore the demographic consequences of site selection by animals on their abundance among habitats. We found that pre and post settling survivorship are important links between the behavioral decisions where to settle and the distribution of a population among habitats. This was demonstrated for 10 generations of the desert isopod, Hemilepistus reaumuri, in three habitats in the Negev Desert, Israel. The populations exhibit low survivorship before settling (12%) and high survivorship (55%) after settling. According to our model this implies high site selection. Theoretical considerations and the case study led us to suggest the following relationship among settling, demography and habitat selection: 1) Individuals search for suitable settling sites to inhabit and reproduce. 2) Their decision where and when to settle is a cost benefit decision. They weigh the benefit of searching for a high quality site against mortality due to increased searching time. 3) The individual's decision to settle determines the pre and post settling survivorship pattern. 4) Survivorship pattern dictates density pattern in time and space. 5) Density pattern in a given habitat determines its quality for the individual. 6) Settling selection among habitats and the number of safe sites controls the distribution of densities among habitats.     

Dealing with uncertain absences in habitat modelling: a case study of a rare ground-dwelling parrot

In the development of a species distribution model based on regression techniques such as generalized linear or additive modelling (GLM/GAM), a basic assumption is that records of species presence and absence are real. However, a common concern in many studies examining species distributions is that absences cannot be inferred with certainty. This is particularly the case where the species is rare, difficult to detect and/or does not occupy all available habitat considered suitable. The western ground parrot ( Pezoporus wallicus flaviventris ) of southern Western Australia, Australia, is a case in point, as not only is it rare and difficult to detect, but it is also unlikely to occupy all available suitable habitat. A recent survey of ground parrots provided the opportunity to develop a predictive distribution model. As the data were susceptible to false absences, these were replaced with randomly selected 'pseudo' absences and modelled using GLM. As a comparison, presence-only information was modelled using a relatively new approach, MAXENT, a machine-learning technique that has been shown to perform comparatively well. The predictive performance of both models, as assessed by the receiver operating characteristic plot (ROC) was high (AUC > 0.8), with MAXENT performing only marginally better than the GLM. These approaches both indicated that the ground parrot prefers areas relatively high in altitude, distant from rivers, gently sloping to level habitat, with an intermediate cover of vegetation and where there is a mosaic of vegetation ages. In this case, the use of presence-only information resulted in the identification of important environmental attributes defining the occurrence of the ground parrot, but additional factors that account for the inability of the bird to occupy all suitable habitat should be a component of model refinement.     

Biogeographic variation in nest placement: a case study with conservation implications

Abstract. Local habitat characteristics are often used to describe a species' niche despite the fact that habitat use can vary across the geographical range. We sought to quantify variation in habitat preferences by asking how nesting habit varies within and between populations of Bell's vireo ( Vireo bellii ) across its geographical range. Analyses of detailed nest placement data from three localities (Kansas, eastern New Mexico and western New Mexico) showed a general trend towards use of dense vegetation. However, there was substantial variation in nest placement and vegetation at nest sites between localities. Furthermore, a review of nest placement data from the literature shows strong differences in nest heights and species of trees even between populations less than 100 km apart. We evaluate these results in light of conservation and suggest that to be most effective, habitat conservation plans should be based on data collected at the locality where the population of interest occurs.     

城镇化背景下河流生境评价——以深圳市为例

城镇化背景下,河流生态系统退化趋势明显,有效评价河流生境状况是修复和保护河流生态系统健康的重要基础。深圳市作为全国经济发展的窗口城市,河流生境的调查研究十分匮乏。因此,为阐明深圳市不同城镇化程度的流域河流生境的差异与主要影响因素,对深圳市两个代表性流域的河流生境展开了研究。针对深圳市河流的生境特点,于2019年丰水期（8月）和枯水期（11月）对城镇化程度较高的深圳河流域的13个样点和城镇化程度较低的坪山河流域12个样点河段的生境状况进行定量调查与评价。采用综合评价法,从河床、河道和河岸带3个方面选取10个生境指标,构建深圳市河流生境评价指标体系和评价方法。结果表明：深圳河流域河流生境质量总体较差,生境评价等级为"良"、"中"、"差"的样点河段分别占7.7%、38.5%、53.8%;坪山河流域河流生境质量总体较好,生境评价等级为"优"、"良"、"中"、"差"的样点河段分别占8.3%、41.7%、41.7%、8.3%。方差分析结果表明两次调查河流生境状况无显著性差异,短时间跨度内河流生境状况变化较小;两个流域河流生境状况差异显著,城镇化程度较低的坪山河流域河流生境质量显著好于城镇化程度较高的深圳河流域。河流生境评估指标主成分分析结果表明人类活动强度、河岸稳定性、河道变化、底质、河岸土地利用及植被多样性是影响深圳市河流生境变化的主要因子。本文对河床、河道、河岸带3个方面分别提出针对性的修复建议,对深圳市河流的生境修复和保护具有重要的指导作用。     

桥边河大型底栖动物生境适宜性

构建精度高,适用性强的水生生物生境适宜性评价模型,为河流生境质量评价和生境修复提供理论依据。以长江一级支流桥边河为例,采用典范对应分析和独立性分析,筛选出影响桥边河大型底栖无脊椎动物优势种河蚬生境质量的关键化学因子和物理因子,利用广义加性模型与多项式拟合模型构建生境因子与生物选择的关系。结果表明:(1)影响桥边河河蚬生境质量的主要因子为COD_Mn、TN、DO、Tur (浊度)和Dep (水深);其中COD_Mn、TN、Tur、Dep与大型底栖无脊椎动物分布成负相关,DO与大型底栖无脊椎动物分布成正相关;(2)桥边河流域河蚬的最适宜COD_Mn含量为1.228 mg/L,最适宜TN含量为0.269 mg/L,最适宜DO含量为11.170 mg/L,最适宜Dep为0.3 m,最适宜Tur为1.130 NTU。(3)线性拟合情况下两种方法均适用;非线性拟合情况下广义加性模型较优于传统多项式拟合模型,且GAM模型在处理离散程度大的数据集时,可以很好的规避多项式拟合过程中出现的过拟合现象。研究显示,运用GAM模型可以更加精确、合理的模...     

土地利用变化对鸟类栖息地连通性的影响——以鄂州市为例

土地利用变化是造成栖息地破碎、缺失与退化的重要原因。生态网络能保护重要栖息地,促进栖息地之间的物质与能量流动,对区域土地利用规划和生物多样性保护具有重要意义。以鄂州市为研究区,基于CLUE-S模型预测现状延续、生态保护和城市扩张3种土地利用情景,将生境质量作为遴选生境斑块的依据之一,以鸟类最大迁徙距离为阈值构建生态网络,从连通概率指数PC和斑块重要性指数dPC两方面,探讨土地利用变化对鸟类栖息地连通性的影响。结果表明：(1)不同情景的地类数量和空间结构均有差异,与生态保护相比,城市扩张情景的建设用地增加11603.52 hm~2,林地、耕地和水体减少5041.8 hm~2、2540.16 hm~2、3385.8 hm~2,新城区、山地风景区与水体周边是主要变化区域;(2)现状延续和城市扩张情景的生境斑块降至235块和216块,网络出现破碎化,生态保护情景增至367块,网络结构完整但空间位置改变;(3)2004—2024年PC表现为先上升后下降再上升的趋势,生态保护的PC高于现状延续和城市扩张,且利于保护短距离迁徙鸟类;(4)生态保护情景边缘型和关键小型斑块得到保护,第一等级斑块增加,城...     

Horned grebe habitat use of constructed wetlands in Alberta,Canada

Wetland degradation has resulted in declines in populations of aquatic birds throughout North America. Horned grebe (Podiceps auritus), a migratory diving bird experiencing population decline, may benefit from wetland construction. We examined horned grebe use of borrow pits (ponds created during highway construction) in Alberta, Canada. Our goals were to document patterns of occurrence and breeding success of grebes on borrow pits and to determine if occupied and unoccupied sites differed in local habitat or landscape characteristics. In May 2003 and 2007, 330 constructed ponds were surveyed for horned grebes. We chose 100 occupied and 100 unoccupied ponds for additional surveys in 2007 and 2008, and collected habitat and landscape data for these sites. We used generalized linear mixed model and generalized linear model regression, coupled with Akaike's Information Criterion, to determine which environmental variables were most effective in explaining occurrence of horned grebes. The best model included all measured local and landscape habitat features. Horned grebes occurred on 36% of ponds in May 2003 and 2007, and chicks were produced on 74.5–81.3% of occupied ponds in 2007 and 2008. Grebes occupied larger ponds with more emergent and riparian vegetation and avoided ponds that supported beavers, contained human structures, and were primarily surrounded by forest within 1 km. On ponds with grebe pairs, chicks were produced more often on sites surrounded by more riparian vegetation. We conclude that the construction of small wetlands offers a promising means of increasing breeding habitat for horned grebes and present specific recommendations for breeding pond construction. © 2012 The Wildlife Society.     

Syntaxonomic diversity as an indicator of ecological diversity — case study Vranica Mts in the Central Bosnia

Syntaxonomic diversity (SD) represents the number of plant communities (phytocoenoses) in certain area. Plant communities as organized systems of populations of various coexisting plant species inhabiting same or similar habitat in the function of time. SD is one of the best indicators of the state and potential carrying capacity of every ecosystem and an attribute of total ecological diversity. In general, level of syntaxonomic diversity indicates habitat heterogeneity and diversity. This could have significant importance in the categorization of habitat values in accordance with European Nature Information System (EUNIS) criteria. The results presented in this paper indicate without any doubt high natural values of mountain range Vranica in Bosnia and Herzegovina. One of the best proofs is an extremely high level of syntaxonomic diversity. In this area covering just 288 km², vegetation is differentiated into 9 formations, 28 classes, 44 orders, 73 alliances and 165 associations. This represents 85% of all classes, 73% of all orders, 65% of all alliances, and 53% of all associations of vegetation in Bosnia and Herzegovina, or 35% of all classes in vegetation diversity in Europe. Going from the level of class to the level of order, the number of syntaxa increases for 61%, from order to alliance for 60%, and from alliance to association for 44.24% (average 55%). SD index is very high and it is 0.5729. This means that on each km² contains 0.5729 syntaxa.     

Life-history variation in closely related generalist predators living in the same habitat: a case study with three Cyclosa spiders

1. Generalist predators sharing similar food resources and phenologies as well as having no competitive interactions are expected to have a similar life-history pattern, but some closely related web spiders show different life-history traits. The present paper clarifies possible selection pressures affecting life-history traits of the three coexisting Cyclosa spiders and explores the significance of the life-history variation.
2. Cyclosa argenteoalba had lower daily survival rate and higher growth rate, C. sedeculata had higher daily survival rate and lower growth rate, and C. octotuberculata showed intermediate levels. This implies that the selection pressures these spiders experience differ appreciably even in the same habitat.
3. The significance of the life-history characteristics of the three species was evaluated by general life-history theories. Cyclosa argenteoalba showed distinguishing reproductive traits: shorter time to maturation, larger reproductive effort, larger relative clutch size, decreased clutch size with the number of clutches, and smaller egg size. These characteristics may have evolved in response to the larger ratio of juvenile to adult survivorship. Cyclosa octotuberculata had a clutch size much larger than the other two species, but relative clutch sizes accounting for body size were similar between C. octotuberculata and C. sedeculata . Also, the two species showed a similar time to maturation despite having different selection pressures. Probably, higher growth rate compensates for lower survivorship, leading to the similarity in some reproductive traits.     

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

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.