Microhabitat selection of ostracods in relation to predation and food

Experiments with the cyprinid fishVimba vimba as predator and the ostracodsCypridopsis vidua, Darwinula stevensoni andCytherissa lacustris as prey show that conspicuous coloration enhances predation risk for the ostracods. When the ostracods are allowed to retreat into sediment, risk is markedly reduced. ostracods show clear microhabitat preferences which are influenced by habitat structure and food supply. Exposed plant surfaces are visited only if they bear food and if the ostracods are not satiated.     

Behaviour and resource use of two competing vole species under shared predation risk

Indirect interaction between two competing species via a shared predator may be an important determinant of population and community dynamics. We studied the effect of predation risk imposed by the least weasel Mustela nivalis nivalis on space use, foraging and activity of two competing vole species, the grey-sided vole Myodes rufocanus, and the bank vole Myodes glareolus. The experiment was conducted in a large indoor arena, consisting of microhabitat structures providing food, shelter, trees for refuge and separated areas with high and low predation risk. Voles were followed for 5 days: 2 days before, 1 day during and 2 days after the presence of weasel. Our results suggest an effect of weasel presence on the vole community. Voles of both species shifted their activity from risky to less risky areas, climbed trees more often and were less active. Seed consumption was not affected by weasel presence. The time spent in the risky and less risky area did not differ between species, but bank voles spent more time in trees than grey-sided voles. Males of both species were more exposed to predation risk than females, i.e. generally spent more time in the risky area. Proportion of time spent in the risky area, the use of area, trees and food stations were sex dependent. Activity and use of trees were species dependent. We found no evidence for despotic distribution between our two species, although bank voles seemed to be more affected by coexistence, since they lost weight during the experiment. Based on our results we conclude that predator response was largely similar between species, while the sex-specific responses dominated. Besides a stronger escape response in the bank vole, the strongest individual differences were sex specific, i.e. males were more prone to take risks in space use and activity.     

Influences of seasons and dietary composition on diurnal raptor habitat use in Chembe Bird Sanctuary,Zambia: Implications for conservation

Diurnal raptor habitat use has conservation implications due to environmental and anthropogenic interactions. Three tree-nesting diurnal raptors, black kites (Milvus milvus), steppe buzzards (Buteo vulpinus) and African fish eagles (Haliaeetus vocifer), were studied from December 2016 to October 2017. The objective was to determine factors influencing diurnal raptor habitat selection and use in and around Chembe Bird Sanctuary of Kalulushi district, Zambia. We surveyed for birds in ten randomly selected 200 × 200 m sample plots in each of the five stratified sampling units (miombo woodland, grasslands, human settlements, Lake Chembe and marsh). Seasons and dietary composition variably influenced the distribution, habitat selection and use by raptors. The three raptors devised a suit of behaviours to curtail challenges associated with seasonal food and water availability, and anthropogenic disturbances. There is a need to promote multi-stakeholder engagement and involvement in raptor conservation.     

Caterpillars escape predation in habitat and thermal refuges

1. Climate and, therefore, abiotic conditions, are changing rapidly, and many ecological interactions depend on them. In this study, how abiotic conditions mediate a predator–prey interaction were examined. 2. Caterpillars of Platyprepia virginalis (Boisduval) (Arctiidae) were found previously to be more abundant in wet habitats and thick litter cover compared with drier habitats and little or no litter. We hypothesised that wet litter provided caterpillars with refuges from an important ant predator, Formica lasioides. It was further hypothesised that caterpillars would be able to move at lower temperatures than ants, thus providing them with a thermal refuge. 3. In the lab, caterpillars were more likely to escape ant predation and survive on wet litter and at lower temperatures. At all temperatures, ant recruitment was lower in wet litter than dry litter although ants were more active on litter than bare soil. Thus, wet litter may serve as a habitat refuge for caterpillars from ants. 4. Caterpillars were able to maintain activity at temperatures 8–14 °C lower than F. lasioides. Thus colder temperatures may serve as a thermal refuge for caterpillars from ants. 5. It was hypothesised that caterpillars can escape ant predation when precipitation causes wet litter and at temperatures that they experience commonly in the field. This mismatch between caterpillars and their predators in ability to tolerate wet litter and low temperatures may affect their field distribution and abundance. Expected future warmer and drier conditions may not provide these refuges.     

Resource partitioning in sympatric delphinids: space use and habitat preferences of Australian snubfin and Indo-Pacific humpback dolphins

1. Many species of delphinids co-occur in space and time. However, little is known of their ecological interactions and the underlying mechanisms that mediate their coexistence. 2. Snubfin Orcaella heinsohni, and Indo-Pacific humpback dolphins Sousa chinensis, live in sympatry throughout most of their range in Australian waters. I conducted boat-based surveys in Cleveland Bay, north-east Queensland, to collect data on the space and habitat use of both species. Using Geographic Information Systems, kernel methods and Euclidean distances I investigated interspecific differences in their space use patterns, behaviour and habitat preferences. 3. Core areas of use (50% kernel range) for both species were located close to river mouths and modified habitat such as dredged channels and breakwaters close to the Port of Townsville. Foraging and travelling activities were the dominant behavioural activities of snubfin and humpback dolphins within and outside their core areas. 4. Their representative ranges (95% kernel range) overlapped considerably, with shared areas showing strong concordance in the space use by both species. Nevertheless, snubfin dolphins preferred slightly shallower (1-2 m) waters than humpback dolphins (2-5 m). Additionally, shallow areas with seagrass ranked high in the habitat preferences of snubfin dolphins, whereas humpback dolphins favoured dredged channels. 5. Slight differences in habitat preferences appear to be one of the principal factors maintaining the coexistence of snubfin and humpback dolphins. I suggest diet partitioning and interspecific aggression as the major forces determining habitat selection in these sympatric species.     

Implications of floral resources for predation by an omnivorous lacewing

Understanding the relationship between a predator and its prey requires consideration of the other food resources used by the predator. In the case of true omnivores, these include plant-provided foods such as leaf tissue and nectar. The presence of plant resources can increase or decrease predation depending on the degree to which they are complementary to, or substitutable for, the prey. This has implications for the role of omnivores in biological control and some groups, notably heteropteran bugs and phytoseiid mites, have been studied in this context. However, few experiments have considered the effects of plant resources both on prey consumption by individual omnivores (which have an immediate effect on the prey population) and on attributes such as longevity and fecundity which act over the longer term to affect predation at the population level. In this study, a model system comprising an omnivorous adult lacewing (Micromus tasmaniae), buckwheat flowers and aphid prey was used to investigate how floral resources affected per capita predation rate, longevity and fecundity of the lacewing. Flowers reduced prey consumption. In the absence of prey, longevity was higher for lacewings with flowers than those without. In an experiment where aphids were provided in abundance, lacewing fecundity was unaffected by flowers. However, when aphids were less abundant, providing flowers decreased the pre-oviposition period and increased the daily oviposition rate. The results demonstrate that floral resources can mediate omnivore–prey relationships and that, in the context of biological control, their effects may be either positive or negative.     

Niche partitioning and the effect of interspecific competition on microhabitat use by two sympatric galaxiid stream fishes

1. Numerous interacting abiotic and biotic factors influence niche use and assemblage structure of freshwater fishes, but the strength of each factor changes with spatial scale. Few studies have examined the role of interspecific competition in structuring stream fish assemblages across spatial scales. We used field and laboratory approaches to examine microhabitat partitioning and the effect of interspecific competition on microhabitat use in two sympatric stream fishes (Galaxias‘southern’ and Galaxias gollumoides) at large (among streams and among sites within streams) and small (within artificial stream channels) spatial scales. 2. Diurnal microhabitat partitioning and interspecific competition at large spatial scales were analysed among three sympatry streams (streams with allotopic and syntopic sites; three separate catchments) and four allopatry streams (streams with only allotopic sites; two separate catchments). Electro‐fishing was used to sample habitat use of fishes at 30 random points within each site by quantifying four variables for each individual: water velocity, depth, distance to nearest cover and substratum size. Habitat availability was then quantified for each site by measuring those variables at each of 50 random points. Diet and stable isotope partitioning was analysed from syntopic sites only. Diel cycles of microhabitat use and interspecific competition at small spatial scales were examined by monitoring water velocity use over 48 h in artificial stream channels for three treatments: (i) allopatric G. ‘southern’ (10 G. ‘southern’); (ii) allopatric G. gollumoides (10 G. gollumoides) and (iii) sympatry (five individuals of each species). 3. One hundred and ninety‐four G. ‘southern’ and 239 G. gollumoides were sampled across all seven streams, and habitat availability between the two species was similar among all sites. Galaxias‘southern’ utilised faster water velocities than G. gollumoides in both the field and in channel experiments. Both species utilised faster water velocities in channels at night than during the day. Diet differences were observed and were supported by isotopic differences (two of three sites). No interspecific differences were observed for the other three microhabitat variables in the field, and multivariate habitat selection did not differ between species. Interspecific competition had no effect on microhabitat use of either species against any variable either in the field (large scale) or in channels (small scale). 4. The results suggest that niche partitioning occurs along a subset of microhabitat variables (water velocity use and diet). Interspecific competition does not appear to be a major biotic factor controlling microhabitat use by these sympatric taxa at any spatial scale. The results further suggest that stream fish assemblages are not primarily structured by biotic factors, reinforcing other studies de‐emphasising interspecific competition.     

A new method for immunologically marking prey and its use in predation studies

We introduce a new method for immunologically examining predator gut contents. It differs from previously described gut content analyses because it does not require the development of prey-specific antibody probes. Instead, insect prey were marked with a readily available antigen, rabbit immunoglobulin G (IgG). We then assayed predators that had fed on IgG labeled prey with an enzyme-linked immunosorbent assay (ELISA) using goat anti-rabbit IgG. Of the predator species that fed on the IgG labeled prey, 98.8% of those with chewing mouthparts scored positive for IgG 1 h after feeding. Our prey-labeling ELISA was less efficient for detecting IgG prey remains in predators with piercing/sucking mouthparts. Only 29.5% of these individuals scored positive for rabbit IgG in their guts 1 h after feeding. An additional study was conducted to measure the retention time of IgG-labeled prey in the guts of two species of predators with chewing mouthparts. Results from this experiment showed that the retention time varied depending on the predator and prey species examined. Results from these studies indicate that this marking technique could have widespread use for analyzing the gut contents of predators with chewing mouthparts, but it has limited application for those predators with piercing/sucking mouthparts. This article presents the results of research only. Mention of a proprietary product does not constitute an endorsement or recommendation for its use by the USDA.     

用地紧凑变化对武汉市绿色空间生境质量的影响

城市化以及人类活动所造成的土地利用变化严重影响了城市绿色空间生境质量,从而引起了一系列生态环境危机。如何科学合理协调用地建设与绿色空间生境质量的关系是城市可持续发展的重要内容。尽管当前不少学者探究了建设用地扩张强度、景观格局变化、土地利用类型变化等因素对自然生境的影响,但用地紧凑视角下用地规模、形态、强度等方面如何影响生境质量仍少有研究。以武汉市三个建设时期（2005、2013、2018年）为例,首先从生境适宜度与生境承载力视角出发构建生境质量综合评价体系,围绕土地利用强度以及土地功能布局,构建用地紧凑度评价指标体系;其次依据三个时期生境质量的热点分布情况将样本网格划分为生境冷点区、生境热点区以及生境变化区;最后通过相关性与空间自相关分析,探究生境质量与用地紧凑度的相关性及其在空间上的关联格局。结果表明：（1）武汉市用地紧凑变化对生境质量有消极影响,2005年至2018年生境质量由0.624下降到0.578,其时空分异特征明显,在三个时期内均呈现中心低、边缘高的分布特征,总体上退化速度加快,城市生境质量的提升工作效果不显著,城市发展边界是生境质量退化的重点区域。（2）不同区间生境质量受用地紧凑度影响的程度呈现出明显的差异性,生境冷点区受用地紧凑度影响最为显著,生境变化区内其与建设用地密度、居住用地密度、路网密度、土地聚集度、土地利用多样性、公交站点密度等存在较强的相关性。（3）用地紧凑因子均会对周边区域生境质量产生潜在影响,建设用地密度、土地聚集度、土地利用多样性、用地混合度、路网密度五项指标不仅对所处地块生境质量造成影响,还与周围地块生境质量退化有着密切联系,对生境影响范围较广,用地整合度对生境质量影响较小。研究结果对优化用地格局、维持生境高质量、实现用地高效配置、完善绿色空间生态系统具有重要参考意义。     

Evidence for genetic differences in the offspring of two sympatric morphs of Arctic charr

The sub-arctic Lake Fjellfrøsvatn, northern Norway, has two morphs of Arctic charr that are reproductively isolated because they spawn 5 months apart. The smaller morph (≤14 cm L_F ) is confined to the profundal zone of the lake and the larger morph is mainly littoral. Three hypotheses were tested: (i) the offspring of the profundal Arctic charr grow slower than the offspring of the littoral Arctic charr under identical conditions, thus indicating a genetic basis for the slow growth of the profundal Arctic charr in the wild; (ii) the wild phenotypes of the two morphs are morphometrically different and the differences are persistent in the offspring; (iii) the offspring of the two morphs have different behaviour traits under similar treatments. The first hypothesis was rejected; offspring of the profundal morph grew slightly better than offspring of the littoral morph at 10° C in the laboratory. The second and third hypotheses were supported by the data. Wild-caught fish of the two morphs differed in several morphometric characters and most of the differences persisted in the offspring. In the laboratory, offspring of the littoral morph were more active, more aggressive and more pelagic than offspring of the profundal morph and naive offspring of the profundal morph were more effective in eating live chironomid larvae than were offspring of the littoral morph. The data for morphometry and behaviour, but not growth, provide evidence for genetic differences between the two Arctic charr morphs of Fjellfrøsvatn.     

The landscape of fear as an emergent property of heterogeneity: Contrasting patterns of predation risk in grassland ecosystems

The likelihood of encountering a predator influences prey behavior and spatial distribution such that non‐consumptive effects can outweigh the influence of direct predation. Prey species are thought to filter information on perceived predator encounter rates in physical landscapes into a landscape of fear defined by spatially explicit heterogeneity in predation risk. The presence of multiple predators using different hunting strategies further complicates navigation through a landscape of fear and potentially exposes prey to greater risk of predation. The juxtaposition of land cover types likely influences overlap in occurrence of different predators, suggesting that attributes of a landscape of fear result from complexity in the physical landscape. Woody encroachment in grasslands furnishes an example of increasing complexity with the potential to influence predator distributions. We examined the role of vegetation structure on the distribution of two avian predators, Red‐tailed Hawk (Buteo jamaicensis) and Northern Harrier (Circus cyaneus), and the vulnerability of a frequent prey species of those predators, Northern Bobwhite (Colinus virginianus). We mapped occurrences of the raptors and kill locations of Northern Bobwhite to examine spatial vulnerability patterns in relation to landscape complexity. We use an offset model to examine spatially explicit habitat use patterns of these predators in the Southern Great Plains of the United States, and monitored vulnerability patterns of their prey species based on kill locations collected during radio telemetry monitoring. Both predator density and predation‐specific mortality of Northern Bobwhite increased with vegetation complexity generated by fine‐scale interspersion of grassland and woodland. Predation pressure was lower in more homogeneous landscapes where overlap of the two predators was less frequent. Predator overlap created areas of high risk for Northern Bobwhite amounting to 32% of the land area where landscape complexity was high and 7% where complexity was lower. Our study emphasizes the need to evaluate the role of landscape structure on predation dynamics and reveals another threat from woody encroachment in grasslands.     

Habitat use and behavioural ecology of the juveniles of two sympatric damselfishes (Actinopterygii: Pomacentridae) in the south-western Atlantic Ocean

Spatial distribution, microhabitat use and territorial and feeding behaviours were compared between the juveniles of two sympatric territorial damselfishes Stegastes variabilis and Stegastes fuscus on a small tropical reef in the south-western Atlantic Ocean. Juvenile S. variabilis were most abundant at sites subject to stronger hydrodynamics and with mixed benthic cover, whereas juvenile S. fuscus were most abundant at sheltered sites with dense turf algae cover. No differences regarding feeding habits were detected, with both species preferentially feeding on turf algae. Also, despite similarities in territory area and agonistic encounter rates, the identity and proportion of intruders involved in agonistic interactions differed significantly between species. These interdependent traits suggest strong asymmetric competition, with juvenile S. fuscus dominating high-quality sites and evicting juvenile S. variabilis to low quality, marginal areas of the reef.     

Influence of revegetation on predation rates by introduced red foxes (Vulpes vulpes) in south‐eastern Australian farmland

Interactions between wild carnivore abundance and landscape composition in agricultural landscapes are poorly understood despite their importance to both production and conservation. In Australia, introduced red foxes (Vulpes vulpes) prey on both native species and lambs in the temperate agricultural regions. Historically these areas were extensively cleared of native vegetation. Recently revegetation programmes have been implemented, but there is concern that this may benefit foxes and hence increase their impacts. We used an artificial prey placed in eight revegetated (6–12% cover) and 10 cleared (0–1.5% cover) landscapes of ～700 ha to assess how these landscapes influenced fox predation rates. In June and August 2006 (winter) when we expect fox populations to be relatively stable following juvenile dispersal, predation rates were 1.5–2 times higher in revegetated landscapes than in cleared landscapes. We found no evidence of microhabitat effects on predation rates suggesting these landscape‐level differences were probably due to differences in fox population density. In April 2007 (autumn) the results were more variable, possibly indicating more transient populations including dispersing juveniles at this time. Our results suggest that the impact of foxes on highly vulnerable prey could increase with revegetation. However, the benefits of revegetation to prey may offset negative impacts of foxes and future work is required to assess the likely net effects.     

两种同域分布蹄蝠在开阔度不同的环境中回声定位声波的可塑性

在广西桂林研究了同域分布的大蹄蝠(Hipposideros armiger)和中蹄蝠(H.larvatus)在不同开阔度环境中回声定位声波信号的变化。用超声波仪录制自由悬挂和分别释放于人工"大棚"和"小棚"内飞行的蝙蝠的回声定位声波,使用超声分析软件分析声脉冲时程、主频率及声脉冲间隔,通过重复测量方差分析比较不同状态下的声波参数。结果表明:中蹄蝠声波的主频在悬挂状态下最高,小棚内飞行时次之,大棚内飞行最低;两种蹄蝠声波的脉冲时程和脉冲间隔在悬挂状态下最长,大棚内飞行次之,小棚内飞行最低。总之,这两种蹄蝠的回声定位声波能够随所处状态的变化而变化,可根据生境的复杂度调节声讯号,具有明显的声波可塑性。