Stream habitat fragmentation — a threat to biodiversity

Biodiversity is undisturbed rhithral streams in central Europe is high, with about 1000 resident metazoan species; over 600 insect species occur in the Fulda river (Germany). Longitudinal downstream shift of dominance from rheobiontic to rheophilous and finally to ubiquituos rheoxenic taxa in the potamal is described. Present downstream importance of ubiquituous species probably results from replacement of original potamal communities, present faunas being surrogates. Species losses through human impact are well documented for fish. The case of Plecoptera (10 potamal species either altogether extinct, extinct in Central Europe or extremely endangered) suggests that potamal invertebrates suffered as severe losses as did fish.Human impact on major rivers was so severe also because they occur at distances beyond average dispersal capacity of the fauna, i.e. are widely separate ecological islands, with known risk of species losses. In contrast, faunal exchange between adjacent headwater streams in mountains with intact stream nets is easy, certainly for amphibious insects. However, damage to rhithral streams is becoming increasingly frequent. This fragments stream nets, turning also upper parts of drainage systems into ecological islands, with danger of extinctions. Rhithral biodiversity is thought to be much more endangered by human impact than is presently recognized.     

Flow-induced alterations to fish assemblages, habitat and fish–habitat associations in a regulated lowland river

Understanding the cause–effect response of aquatic biota to hydrological variability is fundamental to the restoration of regulated rivers. Spatio-temporal variation in fish assemblage structure, microhabitat cover and fish–habitat associations were investigated in the main channel of the regulated lower River Murray, Australia, during a prolonged period of low within-channel flows and following a high flow event and flood. Several small-bodied species (e.g. carp gudgeon, Hypseleotris spp.), were abundant and significantly associated with submerged macrophytes during low flows, but were absent or significantly less abundant following flooding, and the loss of these microhabitats. Large-bodied riverine species that spawn in response to increases in flow (e.g. golden perch, Macquaria ambigua ambigua) or spawn and recruit in inundated floodplain habitats (e.g. common carp, Cyprinus carpio), exhibited flexible microhabitat use and were significantly more abundant following flooding. In the lower River Murray, high flow events appear integral in structuring fish assemblages, indirectly influencing the abundance of small-bodied fish by re-structuring macrophyte cover and directly influencing the abundance of large-bodied species by facilitating critical life history processes (e.g. recruitment). These results highlight species-specific differences in cause–effect responses to flow variability and have implications for managing flow in regulated rivers.     

Can postmining revegetation create habitat for a threatened mammal?

Most revegetation conducted for biodiversity conservation aims to mimic reference ecosystems present predisturbance. However, revegetation can overshoot or undershoot targets, particularly in the early stages of a recovery process, resulting in conditions different from the reference model. Revegetation that has, as yet, failed to fully meet revegetation targets may, nonetheless, provide habitat for threatened species not present in reference ecosystems. To investigate this possibility, we surveyed Quokka (Setonix brachyurus), a threatened macropod, in a mining landscape in south‐western Australia. We established four sites in each of riparian forest, which is the preferred habitat of quokkas but is not mined, mid‐slope forest, which is the premining reference ecosystem but is not suitable habitat for quokkas, and revegetated forest on mine pits 16–21 years postmining. We recorded quokkas in all riparian forest sites and two revegetated forest sites but not in any mid‐slope forest sites. Occupied revegetated sites had greater cover between 0 and 2 m and were spatially closer to riparian forest than unoccupied revegetated sites, suggesting predation pressure was likely influencing which mine pits were occupied. Our study demonstrated postmining revegetation can provide new habitat for a threatened species and suggested that revegetating a small proportion of sites to provide new habitat for threatened species could be considered as a management option in some scenarios. This could improve landscape connectivity and increase both the area of available habitat and between‐site heterogeneity, which could all potentially increase the ability of revegetation to conserve biodiversity.     

Speciation: more likely through a genetic or through a learned habitat preference?

A problem in understanding sympatric speciation is establishing how reproductive isolation can arise when there is disruptive selection on an ecological trait. One of the solutions that has been proposed is that a habitat preference evolves, and that mates are chosen within the preferred habitat. We present a model where the habitat preference can evolve either by means of a genetic mechanism or by means of learning. Employing an adaptive-dynamical analysis, we show that evolution proceeds either to a single population of specialists with a genetic preference for their optimal habitat, or to a population of generalists without a habitat preference. The generalist population subsequently experiences disruptive selection. Learning promotes speciation because it increases the intensity of disruptive selection. An individual-based version of the model shows that, when loci are completely unlinked and learning confers little cost, the presence of disruptive selection most probably leads to speciation via the simultaneous evolution of a learned habitat preference. For high costs of learning, speciation is most likely to occur via the evolution of a genetic habitat preference. However, the latter only happens when the effect of mutations is large, or when there is linkage between genes coding for the different traits.     

Can roadside habitat lead monarchs on a route to recovery?

The Eastern North American monarch butterfly population has severely declined over the past decade. The decreasing availability of larval host plants (milkweeds) due to the use of herbicide-tolerant crops has been implicated in this decline. Roadsides could provide additional habitat for monarchs. In this study we document the occurrence of milkweed and monarchs on roadsides, and discuss whether roadsides are appropriate targets for monarch habitat restoration. We sampled roadside rights-of-way in the Upper Midwestern U.S. during the summer of 2015 to estimate the abundance, distribution, and diversity of milkweeds and the extent to which monarchs use these milkweeds. We then compared monarch densities in roadsides to other habitat types and modelled immature monarch densities based on several site characteristics. Our findings suggest that roadsides have conservation potential for monarchs, especially when other habitat is scarce and if wildlife-friendly management practices are enacted. Milkweeds were found on ~60% of roadside transects. Asclepias syriaca was the most common of the seven species encountered, occurring on 97% of transects with milkweed. Immature monarchs were observed in roadsides, but in lower densities than other habitats during the same time period. At lower milkweed densities, immature monarch density per unit area is positively correlated with milkweed density. However, milkweed density weakens as a predictor of immature monarch density over ~0.6 plants per m², possibly indicating a saturation effect.     

Tourism impairs tiger beetle (Cicindeldae) populations – a case studyin a Mediterranean beach habitat

Adult activity and larval development of Lophyridia concolor (Dejean) was examined in three sections of a marine beach: (1) an undisturbed section; (2) a section occasionally used by tourists; and (3) a heavily disturbed beach section. Although the activity of adult tiger beetles was similar at all three sites in spring, it diverged during the tourist season. The adults reached a high activity with two maxima on the natural beach, but it was 40% lower in the occasionally used section. The adult activity decreased abruptly without visible maxima in the tourist area. Larval activities showed similar trends. First and second instar larvae were practically absent from the heavily disturbed section. The reduced tiger beetle activity was most likely caused by disturbance and modification of habitat by the tourists. Mechanisms of this impairment are discussed. The results might be of importance for several beach inhabiting invertebrates in the Mediterranean area. Persistently high levels of tourist traffic on beaches might lead to local extirpation, as the decline of Lophyridia a. aphrodisia (Baudi), another Turkish tiger beetle species, shows.     

Does the modern urbanized sleeping habitat pose a breast cancer risk?

Due to its disruptive effects on circadian rhythms and sleep deprivation at night, shiftworking is currently recognized as a risk factor for breast cancer (BC). As revealed by the present analysis based on a comparative case-control study of 1679 women, exposure to light-at-night (LAN) in the "sleeping habitat" is significantly associated with BC risk (odds ratio [OR]?=?1.220, 95% confidence interval [CI]?=?1.118-1.311; p?相似文献   

Brackish meltponds on Arctic sea ice��a new habitat for marine metazoans

Meltponds on Arctic sea ice have previously been reported to be devoid of marine metazoans due to fresh-water conditions. The predominantly dark frequently also green and brownish meltponds observed in the Central Arctic in summer 2007 hinted to brackish conditions and considerable amounts of algae, possibly making the habitat suitable for marine metazoans. Environmental conditions in meltponds as well as sympagic meiofauna in new ice covering pond surfaces and in rotten ice on the bottom of ponds were studied, applying modified techniques from sea-ice and under-ice research. Due to the very porous structure of the rotten ice, the meltponds were usually brackish to saline, providing living conditions very similar to sub-ice water. The new ice cover on the surface had similar characteristics as the bottom layer of level ice. The ponds were thus accessible to and inhabitable by metazoans. The new ice cover and the rotten ice were inhabited by various sympagic meiofauna taxa, predominantly ciliates, rotifers, acoels, nematodes and foraminiferans. Also, sympagic amphipods were found on the bottom of meltponds. We suggest that, in consequence of global warming, brackish and saline meltponds are becoming more frequent in the Arctic, providing a new habitat to marine metazoans.     

The heterospecific habitat copying hypothesis: can competitors indicate habitat quality?

According to the "habitat copying" hypothesis, animals use thereproductive performance of conspecifics to assess habitat suitabilityand choose their future breeding site. This is because conspecificsshare ecological needs and thus indicate habitat suitability.Here, we propose the "heterospecific habitat copying" hypothesis,which states that animals should use public information (i.e.,information derived from the performance of others) from con-and heterospecifics sharing ecological needs. In a correlationalapproach we test some assumptions and predictions of this hypothesiswith a data set from two sympatric bird populations, rollers(Coracias garrulus) and kestrels (Falco tinnunculus), usingthe same nest-boxes and exploiting similar food resources. Sincekestrels are residents and breed earlier, we assumed that theyare dominant over rollers for nest-box acquisition. The environmentappears to be patchy for both species and temporally predictablefor kestrels only. Two results suggest that the use of heterospecificpublic information in breeding habitat selection may be at work:(1) an increase in the reoccupancy probability by kestrels ofprevious roller nests with increasing nest success, and (2)an increase in roller breeding population with increasing localkestrel success. Most of the other observed patterns could beexplained by alternative mechanisms such as natal philopatry,breeding fidelity, conspecific attraction, intraspecific habitatcopying, and the effect of interspecific competition.     

Dispersal of non-myrmecochorous plants by a “keystone disperser” ant in a Mediterranean habitat reveals asymmetric interdependence

In contrast to other plant–animal mutualisms, seed dispersal interactions, and particularly seed dispersal by ants, are generally considered asymmetric, non-specialized relationships in which dispersers depend less on plants than vice versa. Although myrmecochory is well understood in many terrestrial ecosystems, dispersal of non-elaiosome-bearing seeds by ants has barely been studied outside the Neotropics. Aphaenogaster senilis, a common ant in Southern Spain, collects a great variety of non-myrmecochorous diaspores along with insect prey. At our study site, fleshy fruits of Arum italicum, Phillyrea angustifolia and Pistacia lentiscus represent up to one-fourth of the items collected by A. senilis from June to November. However, they are mostly ignored by other ants. In the laboratory, the addition of A. italicum fruits to A. senilis insect-based diet increased male production and both worker and queen pupae size. Seeds were transported up to 8 m away from the mother plant and deposited in a favorable habitat allowing a relatively high proportion of germination. Given important differences in seed production between species, our data suggest that A. senilis removes virtually all seeds of A. italicum, but a negligible fraction of P. lentiscus seeds. We conclude that in contrast to the common view, dispersal of non-myrmecochorous Mediterranean plants by ants might be an important phenomenon. Keystone disperser ants like A. senilis probably obtain an important fitness advantage from non-myrmecochorous diaspore collection. However, plant benefit may vary greatly according to the amount of seeds per individual plant and the existence of alternative dispersal agents.     

Our use,misuse, and abandonment of a concept: Whither habitat?

The foundational concept of habitat lies at the very root of the entire science of ecology, but inaccurate use of the term compromises scientific rigor and communication among scientists and nonscientists. In 1997, Hall, Krausman & Morrison showed that ‘habitat’ was used correctly in only 55% of articles. We ask whether use of the term has been more accurate since their plea for standardization and whether use varies across the broader range of journals and taxa in the contemporary literature (1998–2012). We searched contemporary literature for ‘habitat’ and habitat‐related terms, ranking usage as either correct or incorrect, following a simplified version of Hall et al.'s definitions. We used generalized linear models to compare use of the term in contemporary literature with the papers reviewed by Hall et al. and to test the effects of taxa, journal impact in the contemporary articles and effects due to authors that cited Hall et al. Use of the term ‘habitat’ has not improved; it was still only used correctly about 55% of the time in the contemporary data. Proportionately more correct uses occurred in articles that focused on animals compared to ones that included plants, and papers that cited Hall et al. did use the term correctly more often. However, journal impact had no effect. Some habitat terms are more likely to be misused than others, notably ‘habitat type’, usually used to refer to vegetation type, and ‘suitable habitat’ or ‘unsuitable habitat’, which are either redundant or nonsensical by definition. Inaccurate and inconsistent use of the term can lead to (1) misinterpretation of scientific findings; (2) inefficient use of conservation resources; (3) ineffective identification and prioritization of protected areas; (4) limited comparability among studies; and (5) miscommunication of science‐based findings. Correct usage would improve communication with scientists and nonscientists, thereby benefiting conservation efforts, and ecology as a science.     

Variable fortunes in a patchy landscape —The habitat templet of an insect migrant

Migration by flight is essential for insects living in patchy landscapes and knowledge about variability in habitat patch structure and quality is important for the development of theory concerning insect dispersal polymorphisms. However, few studies provide more than anecdotal evidence about habitat change in time and space and its effects on insect survival and reproduction. Here I show how habitats and resource density of a lygaied bug,Lygaeus equestris, change in a patchy landscape over a seventeen year period. Although habitat patches per se are very stable, there are large temporal fluctuations in per capita food resources. Food seems to be limiting only in some years, and there may be periods of several years when populations change due to weather disturbance. Between-patch variation in reproductive success is large. Furthermore, the relative favourability of patches changes between years. There are also distance effects; in some years distances to suitable hibernation sites affect reproductive success. Long fliers experience more variable success, and sometimes extreme success, when compared with short fliers. The importance of movements from outlying areas also changes with time. The insect is thus faced with a habitat templet which varies strongly on many temporal and spatial scales.     

Winter habitat–space use in a large arctic herbivore facing contrasting forage abundance

We analysed how changes in resource levels influence foraging trade-offs in late winter by wild Svalbard reindeer. Forage plants, and particularly lichens, were less abundant at the overgrazed Brøggerhalvøya compared with the neighbouring Sarsøyra. Strong interactions occurred between habitat selection, home range size, and feeding crater selection. At Brøggerhalvøya, radiocollared females generally selected productive habitat (high summer NDVI; Normalised Difference Vegetation Index). “Immigrants” at Sarsøyra (dispersed from Brøggerhalvøya in early winter) had similar habitat preferences, probably due to past experience. In contrast, “residents” at Sarsøyra were more influenced by abiotic conditions, using habitat with low NDVI, but selecting for high-quality forage (lichens) when cratering. This suggests more quality-based selection at the expense of quantity when forage abundance increases. Habitat–space use relationships also differed between the animal categories, as home range size decreased with availability of preferred habitat. Thus, changes in forage abundance can strongly influence winter habitat–space use interactions in predator-free systems.     

Do birds of a feather flock together? Comparing habitat preferences of piscivorous waterbirds in a lowland river catchment

The aim of the present study was to use the analysis of surface water chemistry to understand vegetation succession pathways in terrestrializing polyhumic lakes. We hypothesized that Sphagnum mire development was accompanied by a decrease in the mineral content in water. A total of 111 vegetation plots along 23 transects were analysed in 11 lakes and adjacent peat lands in the Wigry National Park (NE Poland). The vegetation of the lake-mire systems forms distinct zones: (1) nymphaeid-, bladderwort- and bryophyte-dominated aquatic vegetation; (2) sedge-dominated edge of the Sphagnumcarpet; (3) quaking, extremely poor fen with various Cyperaceae; (4) non-quaking, Eriophorum vaginatum-dominated bog-like vegetation and (5) pine woodland. Surface water corrected conductivity (EC_corr.), pH, COD-KMnO₄ and Ca²⁺, Mg²⁺, Fetot. and SiO₂ were measured along the transects. The environmental gradients best explaining the observed pattern were pH (with the highest values in the lake and the lowest in the bog-like vegetation) and COD-KMnO₄ (showing an inverse direction). At least in some Sphagnum-mires conditions were more minerotrophic than in the lakes. The process of humic lake overgrowing by Sphagnum-mires in NE Poland results in pine woodlands on mineralised peat. The climate conditions in NE Poland, combined with evapotranspiration accelerated by encroaching trees, do not seem to support the development of ombrotrophic bogs.     

How far can a tortoise walk in open habitat before overheating? Implications for conservation

Terrestrial chelonians are threatened worldwide by habitat destruction and illegal harvesting. Tortoises are slow moving animals susceptible to dehydration and overheating during movements in open habitats. Many species inhabit arid steppes where the availability of thermally buffered refuges (e.g. burrows) is a limiting factor. Determining the maximal distance between refuges that individuals can safely traverse during the active season is thus essential. We examined the relationship between body temperature variations and movement patterns in adult Testudo graeca in the arid steppes of Morocco. Using physical and mathematical models, our results suggest that during the active season adults cannot travel more than 1 km without serious risk of overheating. However, radio-tracking suggests that free-ranging individuals are behaviourally limited to 0.5 km trips between refuges. Overall, maintaining a distance less than 0.5 km between refuges (e.g. through bush planting) is essential to limit fragmentation and to retain healthy populations. This restoration would also benefit to many other species that depend on bush-refuges.     

Does habitat fragmentation affect temperature-related life-history traits? A laboratory test with a woodland butterfly

Habitat fragmentation may change local climatic conditions leading to altered selection regimes for life-history traits in small ectotherms, including several insects. We investigated temperature-related performance in terms of fitness among populations of the woodland butterfly Pararge aegeria (L.) originating from populations of a closed, continuous woodland landscape versus populations of an open, highly fragmented agricultural landscape in central Belgium. Female fecundity and longevity were evaluated in a temperature-gradient experiment. As predicted, females of woodland landscape origin reached higher maximum daily fecundity and lifetime number of eggs than did agricultural landscape females at low ambient temperatures, but this reversed at high ambient temperature. Egg weight decreased with temperature, and eggs of woodland butterflies were smaller. Contrary to what is generally assumed, remaining thorax mass was a better predictor of lifetime reproductive output than was abdomen mass. Since we used the F2 generation from wild-caught females reared under common garden conditions, the observed effects are likely to rely on intrinsic, heritable variation. Our results suggest that differential selection regimes associated with different landscapes intervene by intraspecific variation in the response of a butterfly to variation in ambient temperature, and may thus be helpful when making predictions of future impacts on how wild populations respond to environmental conditions under a global change scenario, with increasing temperatures and fragmented landscapes.     

Genetic erosion in a stenotopic heathland ground beetle (Coleoptera: Carabidae): a matter of habitat size?

Two centuries ago large areas of north-west Europe were covered by coherent heathlands which hosted numerous specialized species. Changes in land use made heathlands fragmented and rare, consequently, they are in the focus of nature conservation efforts today. But how large should remaining heathland patches be in order to secure the survival of populations of specialized species? We investigated the genetic diversity at five allozyme loci of Poecilus lepidus, a flightless and stenotopic heathland ground beetle. 29 populations from differently sized heathland patches in north-west Germany were analyzed. Results show a weak but significant genetic differentiation and no evidence for isolation by distance or other patterns of spatial autocorrelation. Linear regression analysis revealed significant relationships between patch size, allelic richness, number of alleles and expected heterozygosity. These findings are explained by severe habitat fragmentation together with strong fluctuations in population size which have been reported for this species in the past. To conserve the vast majority of the species’ genetic diversity for a period of 100 years we suggest to maintain heathland patches of at least 50 ha in size.     

Modeling the potential suitable habitat of Impatiens hainanensis,a limestone-endemic plant北大核心CSCD

Aims Modelling potential distribution ranges of threatened species is of great significance for their conservation. In this paper, the distribution of potential suitable habitat of Impatiens hainanensis, a limestone-endemic and endangered plant in Hainan Island, was studied to provide scientific basis for their effective in situ conservation and re-introduction of I. hainanensis. Methods Based on eight occurrence sites and 12 environmental variables, the Maximum Entropy (MaxEnt) algorithm and GIS technology were used to create a model linking the distribution ranges of I. hainanensis with environments. With data on five actual distribution sites and five non-occurrence sites, four model evaluation metrics (area under the receiver operating characteristic curve (AUC), kappa coefficient, true skill statistic (TSS), overall accuracy) were used to evaluate the predictive performance and accuracy of this model. Important findings The results indicated that the indicative value of all four evaluation metrics were above 0.9, indicating that the MaxEnt model can effectively predict the potential suitable habitats of I. hainanensis. Slope, precipitation of the driest quarter and coefficients of precipitation variation were the three main environmental factors influencing the distribution of I. hainanensis. At present, the most suitable habitat includes western and southern parts of Baisha County, the central and southern parts of Changjiang County, the eastern part of the Dongfang City and northeastern Ledong County, accounting for 1.8% of land area on Hainan Island. Since the potential suitable habitat of I. hainanensis is rare and severely fragmented, the protection of this species is urgent. We suggest to collect the seeds of various geographic populations of I. hainanensis to establish a germplasm resource bank. The most suitable habitat of the species, including Tian’an Village and Jiangbian Village in Dongfang City, northeast of Ledong County (Jiaxi Reserve), should be selected as the priority places for future extensive field surveys and re-introduction. © Chinese Journal of Plant Ecology.     

How population loss through habitat boundaries determines the dynamics of a predator–prey system

The increased persistence of predator–prey systems when interactions are distributed through the space has been acknowledged by both empirical and theoretical studies. One salient feature of predator–prey interactions in heterogeneous space, for example, is the existence of cycles with reduced amplitude when compared with a homogeneous landscape. Although the role of spatial interactions in shaping the dynamics of predator–prey systems has been extensively studied, still very few works have focused on the effects of habitat loss and fragmentation on these systems. In this work, we study the population dynamics of a predator–prey system in a single finite habitat with flux at the boundaries. Species movement and growth are described through a reaction–diffusion model with Rosenzweig–MacArthur type local interactions. Conforming with the existing literature, we find that the reduction of habitat size, or increasing of species movement rates equivalently, has the potential to decrease the amplitude of oscillations and even bring the system to a steady coexistence equilibrium above a threshold. We observe, however, situations in which this trend is reversed. This occurs when species movement rates and response at patch boundaries interact to induce non-trivial patterns of species distributions. These distributions are characterized by anti-correlation between predator and prey, creating then spatial refugia for prey. Our results highlight the role of population loss through habitat boundaries in determining the dynamics of predator–prey interactions.