Habitat selection and conservation of Sharpe's longclaw (Macronyx sharpei), a threatened Kenyan grassland endemic

Montane grassland is a severely threatened habitat in Kenya. Despite a high level of faunal endemism, it has received very little conservation attention. We investigated habitat selection in a threatened grassland endemic bird species, Sharpe's longclaw (Macronyx sharpei) (family Motacillidae), in order to understand its likely response to land-use changes. Between November 1995 and May 1996, we studied 41 territories of this species on the Kinangop Plateau in central Kenya. With an overall density of 0.4 birds ha⁻¹, longclaws lived in permanent groups of two to seven individuals. They were sedentary and territorial, with a mean home range size of 0.5 ha. The species avoided non-grassland areas entirely, and within grassland showed a strong preference for short grass with tussocks. Territory sizes and foraging ranges were smaller, and rates of pecking for food higher, in this grassland type than in open short grass or long grass. Land use changes, in particular conversion to cultivation or woodlots and ploughing up of grassland to remove tussocks, pose a serious and immediate threat to this species. Dairy farming is potentially compatible with grassland conservation, and conservation-friendly livestock rearing needs to be promoted through economic incentives, awareness-raising and technical advice.     

Long-term heathland restoration on former grassland: The results of a 17-year experiment

European lowland heaths have declined by up to 80% due to land use change and lack of management. There has been considerable research into the restoration of this threatened habitat. However, long-term outcomes of restoration are poorly understood, especially in situations where past agricultural land use imposes severe constraints on community re-assembly. In 1989 a large-scale experiment was established to examine the effectiveness of five treatments to restore heathland on formerly productive grassland: (i) natural regeneration; (ii) herbicide application to facilitate regeneration; (iii) cultivation and application of seed-rich heathland vegetation; (iv) soil removal and incorporation of heathland topsoil; and (v) heathland translocation. After 17 years the pH of the unamended agricultural soil remained significantly higher than that of the adjacent heathland. All treatments showed different trajectories of vegetation change in the long-term. Natural colonisation by heathland species was slow due to seed limitation, resulting in formation of an acid grassland community. Heathland community assembly was not facilitated by destruction of the initial grassland with herbicide. Incorporation of topsoil had an intermediate effect on pH reduction. This may explain the subsequent failure of the plant community to assemble in the anticipated proportions, and the dominance of leguminous scrub species (Ulex spp.). Turf translocation was effective in reducing pH to the required range and restoring the heathland community in the long-term. However, this technique should only be considered as a means of ‘rescue’ when habitat destruction is otherwise unavoidable. The only practical and sustainable means of increasing heathland extent on former farmland is the application of seed-bearing vegetation cut as part of routine management. However, this technique needs refining in order to establish the full range of characteristic heathland species.     

Landscape occupancy and local population size depends on host plant distribution in the butterfly Cupido minimus

We tested whether the landscape occupancy and local population size of the monophagous butterfly Cupido minimus can be predicted by patch size and isolation of its host plant or by other habitat characteristics. C. minimus and its larval food plant Anthyllis vulneraria are classified as rare and endangered in northern Germany. Adults of C. minimus are ranked as the most sedentary butterfly species in northern Europe.Around the city of Göttingen (Germany), we checked all known locations of A. vulneraria (n=70) in June 2002 for butterfly eggs (in blooming flowerheads) and adult butterflies (within 20-min transects).We found eggs of C. minimus or a high number of adults (>7) in all habitats with A. vulneraria (which are calcareous grasslands) even when isolated up to 2-4 km. In multiple regression analyses, local population size of adult butterflies was positively related to the cover of its larval food plant A. vulneraria explaining 65% of variance. Cover of A. vulneraria increased with increasing habitat area and increasing cover of plant species in flower and decreased with increasing cover of shrub layer. Habitat isolation and further factors describing habitat quality were not related to C. minimus population size or cover of its larval food plant.The results suggest that dispersal ability of C. minimus is greater than expected and that management should focus to increase A. vulneraria patches. For conservation, low impact grazing once a year and removing of excessive shrubs in winter seems to be the most appropriate strategies.     

Habitat loss and the habitat fragmentation threshold: an experimental evaluation of impacts on richness and total abundances using grassland invertebrates

Based on empirical analyses and computer-based modelling, it has been suggested that the impact of habitat loss is essentially independent of habitat fragmentation when >10-30% of the original habitat is left and that habitat fragmentation is influential only when less that this amount remains. This is the threshold effect of habitat fragmentation. In many systems, effects of habitat loss cannot be distinguished from those of habitat fragmentation in a way needed to critically evaluate the existence of the threshold effect. Therefore, we used an experimental model system (EMS) that was constructed to produce multiple micro-landscapes in which the habitat-loss and habitat-fragmentation impacts were potentially distinguishable. We used responses of terrestrial invertebrates to measure the impacts. We did not find an interaction between habitat-loss and habitat-fragmentation effects in the predicted fashion, although it is possible the threshold of habitat loss we used for the experiments (90%) may have still been above a critical level for the invertebrates. The only significant components were a strong ‘edge-centre’ difference in both richness and abundance, and a temporal change in both variables. Thus, in this EMS, there was little support for the threshold phenomenon or for general effects of habitat loss and fragmentation although this conclusion needs to be tempered by the limited duration of the experiment.     

Habitat use and conservation of bumblebees (Bombus spp.) under different grassland management regimes

Declines in the natural populations of several bumblebee species across Britain and Europe are an increasing cause for concern. In this study the habitat use of bumblebees was investigated on Salisbury Plain Training Area, the largest remaining area of unimproved chalk grassland in north-west Europe. Habitat characteristics influencing the overall abundance, species richness and foraging activity of bumblebees included the diversity and abundance of flowering plant species (particularly of favoured forage plants such as Trifolium pratense), vegetation structure and height. It is suggested that different Bombus species respond to these habitat characteristics depending on their specific foraging and nesting requirements, the case of Bombus humilis being especially relevant. The effects of several grassland management practices were considered in terms of their suitability for the conservation of bumblebee habitats. Cattle grazing was shown to be preferable to both sheep grazing and the absence of any management, although the timing and intensity of such grazing was important. Small-scale disturbances caused by vehicle activity were also of value in producing locally abundant forage resources in less intensively managed grasslands.     

Species-specific barrier effects of a motorway on the habitat use of two threatened forest-living bat species

It is generally recognized that roads can adversely affect local animal populations but little is known how roads affect bats. In particular, no study compared the response of bats that differ in foraging ecology to motorways that cut through the breeding habitat. As bats are key species in conservation, such data are urgently needed for designing management plans. Using radio-telemetry, mist netting, and mark-recapture data we investigated the effects of a motorway with heavy traffic on the habitat use of two threatened forest-living bats. We compared barbastelle bats (Barbastella barbastellus), which forage in open space, to Bechstein’s bats (Myotis bechsteinii), which glean prey from the vegetation. Five of six radio-tracked barbastelle bats crossed the motorway during foraging and roost switching, flying through underpasses and directly over the motorway. In contrast, only three of 34 radio-tracked Bechstein’s bats crossed the motorway during foraging, all three using an underpass. Bechstein’s bats, unlike barbastelle bats, never crossed the motorway during roost switching. Moreover, only in Bechstein’s bats individuals foraging close to the motorway had smaller foraging areas than individuals foraging further away, whereas other forest edges had no such effect. Our data show that motorways can restrict habitat accessibility for bats but the effect seems to depend on the species’ foraging ecology and wing morphology. We suggest that motorways have stronger barrier effects on bats that forage close to surfaces than on bats that forage in open space, and discuss the implications of our findings for bat conservation during road construction.     

Experimental establishment of a declining dry-grassland flagship species in relation to seed origin and target environment

Supporting species persistence may involve (re)connecting suitable habitats. However, for many declining species habitat suitability and drivers of establishment are poorly known. We addressed this experimentally for a declining flagship species of dry grasslands in Germany, Armeria maritima subsp. elongata. In three regions, we sowed seeds from each of eight source populations back to their origin and to eight apparently suitable, but currently unoccupied, habitats close to the source populations. Overall, seeds germinated and seedlings established equally well in occupied and potential sites indicating that suitable habitats are available, but lack seed input. Germination and establishment varied among sowing sites. Moreover, seeds from populations of lower current connectivity established less well in new sites, and establishment was more variable among seeds from smaller than from larger populations, possibly reflecting genetic consequences of habitat fragmentation. Further, establishment across different new environments differed between seeds from different populations. As this was neither related to a home-away contrast nor to geographic or environmental distance between sites it could not clearly be attributed to local adaptation. To promote long-term persistence within this dry-grassland meta-population context we suggest increasing the density of suitable habitats and supporting dispersal connecting multiple sites, e.g. by promoting sheep transhumance, to increase current populations and their connectivity, and to colonise suitable habitats with material from different sources. We suggest that sowing experiments with characteristic species, including multiple source populations and multiple recipient sites, should be used regularly to inform connecting efforts in plant conservation.     

Building large-scale spatially explicit models to predict the distribution of suitable habitat patches for the Greater rhea (Rhea americana), a near-threatened species

We developed large-scale spatially explicit models to predict the distribution of suitable habitat patches for the Greater rhea (Rhea americana), a near-threatened species, in two areas of central Argentina with different land use: a grassland area (ca. 4943 km²) mainly devoted to cattle grazing and an agro-ecosystem area (ca. 4006 km²) mostly used for crop production. The models were developed using logistic regression and were based on current records of Greater rhea occurrence coupled with remote sensing data, including land cover and human presence variables. The habitat suitability maps generated were used to predict the suitable habitat patch structure for wild rhea populations in each area. Fifty-one percent of the total grassland area was suitable for the species, being represented by a single large patch that included 62% of the individual locations. In the agro-ecosystem, only 28% of the total area was suitable, which was distributed among four patches. Seventy percent of rhea observations were in suitable habitat, with all rheas grouped in the largest patch. Conservation efforts for preserving wild rhea populations should be focused on maintaining habitats similar to grasslands, which are less profitable for landowners at present. Consequently, the protection of the pampas grasslands, a key habitat for this species as well as for others with similar habitat requirements, will demand strong conservation actions through the reconciliation of interests between producers and conservationists, since the proportion of croplands is increasing.     

The role of fragment area and isolation in the conservation of heathland species

Heathland area in the northwestern part of Belgium has been strongly reduced during the past 200 years, and the remaining heathland is forced back into several small and isolated relics. In this study, we investigated how the fragmentation of these heathlands affects the distribution patterns of heathland plant species. Furthermore, we tested whether differences in patch occupancy patterns could be explained in terms of life history traits related to dispersal capacity and persistence. Multivariate logistic regression models showed that the incidence of almost three quarters of the species was influenced by fragmentation. For the majority of these species, isolation was the most important factor determining their presence or absence in a heathland patch. Differences between the species in isolation-sensitivity could be attributed mainly to differences in seed bank characteristics, with species having a long living seed bank being less affected by isolation. In contrast, species having mechanisms facilitating long distance dispersal were as much affected by isolation as species lacking these mechanisms.Our results suggest that for the majority of the species extinction in a patch can be prevented by dispersal from neighbouring patches. Further isolation of the patches should therefore be prevented and connectivity between the patches needs to be assured. As almost none of the species is affected by a declining patch area, for most even small patches are important for their survival. Hence, conservation efforts should focus not only on large heathlands.     

Dispersal and establishment of floodplain grassland species as limiting factors in restoration

The restoration of grassland and its dependence on the dispersal of characteristic plant species was analysed in the Saale River floodplain near Halle (Germany). Species composition and soil nutrient content were investigated in grassland converted to extensive management in 1989 (“restoration grassland”) and in adjacent grassland that had never been managed intensively (“old grassland”). In two experiments dispersal of Silaum silaus and Serratula tinctoria was studied following introduction of these species into “restoration grassland”. Seedling establishment was recorded and compared with the “old grassland”. Ten years after conversion to extensive management, characteristic floodplain grassland species had only reappeared in locations very close to “old grassland”. There were still differences in soil nutrient content of both grassland sites but a comparison of seedling survival provided evidence that conditions of establishment were similar. However, establishment rates appeared to be low in both grassland types indicating that a large initial input of seeds is required for re-establishment. Seeds of Silaum silaus and Serratula tinctoria were dispersed very short distances. About 75% of the seedlings were found within 1.5 m of parent plants. Management and flooding did not increase dispersal distances. The results strongly suggest that poor dispersal was the main limiting factor in determining the success of restoration. The implications of this result for nature conservation are discussed.     

The effect of two endogeic earthworm species on zinc distribution and availability in artificial soil columns

The objective of this study was to determine the impact of earthworm bioturbation on the distribution and availability of zinc in the soil profile.Experiments were carried out with Allolobophora chlorotica and Aporrectodea caliginosa in 24 perspex columns (∅ 10 cm), filled with 20-23 cm non-polluted soil (OM 2%, clay 2.9%, pH 0.01 M CaCl₂ 6.4), that was covered by a 3-5 cm layer of aged zinc spiked soil (500 mg Zn/kg dry soil) and another 2 cm non-polluted soil on top. After 80 and 175 days, columns were sacrificed and each cm from the top down to a depth of 15 cm was sampled. Earthworm casts, placed on top of the soil, were collected. Each sample was analyzed for total and CaCl₂-exchangeable zinc concentrations.Effects of earthworm bioturbation were most pronounced after 175 days. For A. chlorotica, total and CaCl₂-exchangeable zinc concentrations in the polluted layers were lower with than without earthworms. Total zinc concentrations in the non-polluted layers were higher in columns with earthworms. Casts of A. chlorotica collected on the soil surface showed slightly higher total zinc concentrations than non-polluted soil. Casts were found throughout the whole column. For A. caliginosa there were no differences in total zinc concentration between columns with and without earthworms. CaCl₂-exchangeable zinc concentrations in the polluted layers were lower for columns with earthworms. Casts were mainly placed on top of the soil and contained total zinc concentrations intermediate between those in non-polluted and polluted soil layers.This study shows that different endogeic earthworm species have different effects on zinc distribution and availability in soils. A. chlorotica transfers soil throughout the whole column, effectively mixing it, while A. caliginosa decreases metal availability and transfers polluted soil to the soil surface.     

Role of human-modified habitat in protecting specialist species: A case study in the threatened Florida Scrub-Jay

Habitat specialists are especially vulnerable to habitat alterations in vegetation structure and composition, making them difficult to protect and restore amidst agricultural landscapes. Protection strategies in such cases require information on species’ ability to survive and reproduce on marginal and modified habitat. We examined reproductive success, survival, and foraging efficiency of the Florida Scrub-Jay (Aphelocoma coerulescens), an extreme habitat specialist, in a human-modified habitat - regenerating pasture - along a pasture-native scrub interface. From 1985 to 2003, Florida Scrub-Jays were equally successful at producing young in regenerating pasture and native scrub. Production of eggs, nestlings, fledglings, independent young, and yearlings were not statistically different between territories containing pasture and those containing only scrub. Similar trends were observed for nest success and survival. When in pasture, individual jays were significantly more efficient at capturing small prey items, but significantly less efficient at capturing medium and large prey items. Availability of small prey items was significantly higher in pasture than in scrub; availability of medium and large prey items was not significantly different between habitat types. We conclude that regenerating pasture provides suitable supplemental habitat for Florida Scrub-Jays when in close proximity to native scrub, suggesting a novel conservation strategy for maintaining and potentially increasing local populations in fragmented agricultural settings. This case study illustrates how a broadened definition of ‘suitable habitat’ may augment existing conservation strategies for specialist species facing substantial and rapid modification of their native habitat.     

Effects of bush encroachment on an assemblage of diurnal lizard species in central Namibia

Bush encroachment is a serious environmental and economic problem in Namibia, but little is known about impacts on native reptile diversity. Area-confined visual surveys were used to examine a diurnal lizard assemblage in central Namibian commercial ranchlands. Surveys were conducted in plots of open savanna habitat and proximal bush-encroached habitat. The following four species comprised 97.5% of all lizard observations: Pedioplanis undata, Mabuya varia, M. striata, and Lygodactylus bradfieldi. Pedioplanis undata was terrestrial, and the remaining three species were largely arboreal in our study plots. Mabuya varia was found in all savanna plots but was absent from all bush-encroached plots. Two species (P. undata and L. bradfieldi) were less abundant in bush-encroached plots. One species (M. striata) was more abundant in bush-encroached plots than in open savanna plots. Arboreal lizards demonstrated an avoidance to invasive woody plant species. Decreased diversity of habitat structure in bush-encroached habitats appears to influence native savanna lizard assemblages. Our results are consistent with accumulating evidence suggesting that bush encroachment and its associated ecological impacts are reorganizing savanna ecosystems throughout southern Africa.     

The effects of cattle grazing on tall-herb fen vegetation and molluscs

The effects of light year-round cattle grazing on tall-herb fen vegetation and wetland molluscs were compared to the effects of non-intervention over a period of four years using grazing exclosures. The distribution of cattle within the area of fen was investigated by plotting the position of the herd at 3-4 day intervals throughout the year. Cattle distributed themselves randomly throughout the fen in spring, autumn and winter, but showed a more aggregated distribution in summer. Grazing reduced the biomass of Phragmites australis and increased stem densities of Glyceria maxima, resulting in a shift of dominance from Phragmites to Glyceria. Plant species-richness was also significantly higher in areas open to grazing.Grazing decreased total densities of molluscs and substantially reduced densities of the rare snail Vertigo moulinsiana. V. moulinsiana was particularly associated with areas of fen that had a high water table and high biomass of ungrazed Carex riparia. However, because of the patchy nature of the grazing, V. moulinsiana survived at reasonably high densities in patches of ungrazed vegetation within the grazing unit.     

Comparative demography of a rare species in Florida scrub and road habitats

Anthropogenic habitats can offer opportunities for expansion of rare species. The federally listed herb Hypericum cumulicola is virtually restricted to natural gaps within fire-maintained Florida scrub, but also occurs within and along sandy roads traversing scrub. To test the hypothesis that sandy roads provide suitable habitat for H. cumulicola, we compared the demographic performance of scrub and road populations at the Lake Wales Ridge State Forest and Archbold Biological Station in south-central Florida. Twice a year in February and August 1997-2006, we assessed recruitment and survival; annually in August we also measured maximum height and estimated reproductive output of tagged individuals. Scrub population dynamics were more stable than road populations. Recruitment increased with rainfall in scrub populations, but not always in road populations. Compared with scrub populations, road populations were weedier, with more variable life spans, earlier flowering, and higher fecundity. Germination rates did not differ between individuals from different habitats, but varied depending on simulated weather conditions. The weedier life history may reflect a divergent selective environment (and perhaps an evolutionary and ecological trap). Alternatively, adaptive plasticity in H. cumulicola may allow the species to maintain populations in anthropogenic habitats that can serve as refugia for fire-suppressed scrub populations.     

Habitat associations of bats in Northern Ireland: implications for conservation

Agricultural intensification in Northern Ireland has brought about large-scale changes to the landscape with a detrimental effect on biodiversity. Between 1996 and 1998, we surveyed a stratified random sample of 1 km squares for bats using a spot-sample technique and time expansion bat detector to establish linear and area habitat associations. Bats strongly selected water bodies with bankside vegetation, treelines, and deciduous and mixed woodland edge, avoiding open areas such as upland/unimproved grassland and improved grassland. Of three sympatric pipistrelle species (Pipistrellus pipistrellus, P. pygmaeus and P. nathusii), two were shown to forage in different habitats; P. pipistrellus being more of a ‘generalist’, foraging in a wider variety of habitats than P. pygmaeus, a ‘specialist’ which foraged in a smaller range of habitats. Nyctalus leisleri selected parkland/amenity grassland, deciduous woodland edge and rivers/canals and avoided improved grassland, hedgerows, whilst Myotis spp. selected deciduous woodland centre, lake/reservoir margins and rivers/canals. Reduction in area and quality of inland water, deciduous woodlands and field boundaries in Northern Ireland may impact on bat populations. Habitat management should focus on improving those habitats which are selected by bats, including the maintenance and enhancement of connecting linear habitats.     

From genetic diversity and structure to conservation: Genetic signature of recent population declines in three mouse lemur species (Microcebus spp.)

The exceptional biodiversity of Madagascar is threatened by anthropogenic landscape changes that took place during the 2000 years of human colonization. This study focuses on the influence of geographic distance and forest fragmentation on genetic diversity and population differentiation of three rare, nocturnal, arboreal lemur species in northwestern Madagascar. Historic declines in population sizes as a consequence of forest fragmentation are quantified and dated. Eighteen sites were visited, and a total of 205 Microcebus ravelobensis, 45 M. bongolavensis and 78 M. danfossi were genotyped with eight microsatellite loci. Genetic differentiation among the sites, as measured by F_ST, ranged from 0.01 to 0.19. These values were significant in almost all cases and indicated genetic structure in the samples. Isolation-by-distance was detected in one species and a STRUCTURE analysis indicated that fragmentation further promoted genetic differentiation. Bayesian methods revealed that populations from all three species underwent a major demographic collapse of around two orders of magnitude. This decrease probably began after the arrival of humans, most likely within the last 500 years. This result suggests that anthropogenic changes may have been limited during the first 1500 years of human colonization in all three ranges. Two of the study species (M. danfossi, M. bongolavensis) lack effectively protected areas in their ranges. Consequently, quick conservation actions are now needed in order to secure the remaining genetic diversity of these species.     

Status, distribution and definition of mycologically important grasslands in Scotland

In northern Europe, unimproved grasslands provide the habitat for a diverse group of fungi, including members of the genera Camarophyllopsis, Hygrocybe, Entoloma and Dermoloma, and the families Clavariaceae and Geoglossaceae. These fungi are currently the focus of international conservation concern, owing to rapid declines in the availability of suitable habitat. To assess their status in Scotland, 621 field surveys were undertaken on a total of 511 sites, distributed throughout the country. Taxa were found to differ substantially in abundance; for example, whereas five Hygrocybe taxa were recorded at a single site, seven taxa were recorded on more than 200 sites. The number of Hygrocybe taxa per site was found to be positively correlated with number of Clavariaceae taxa (r=0.60); however, the total number of Entoloma taxa was poorly correlated with diversity of other groups (r<0.35). Detrended correspondence analysis (DCA) of field data highlighted variation in composition of fungal communities; in particular, Entoloma taxa were found to cluster together, and were rarely found in association with Geoglossaceae. The data were used to critically examine current approaches to defining the conservation importance of grassland sites on the basis of their mycota. Species accumulation curves indicated that more than 16 visits may be required to fully characterize the fungal diversity of a site. Different groups of fungi also displayed constrasting patterns of seasonal variation in sporome production; peak diversity values for Geoglossaceae and Clavariaceae tended to occur later in the year than for Hygrocybe and Entoloma. Such results indicate that intensive, multiple surveys over prolonged periods are required to accurately define the conservation value of grassland sites. However, these preliminary data suggest that the unimproved grasslands of Scotland are of exceptional importance for fungal conservation, compared with other countries of northern Europe.     

Does seed dispersal by sheep affect the population genetic structure of the calcareous grassland species Bromus erectus?

This study investigates the contribution of the traditional land-use system “sheep herding” (transhumance) to the gene flow among populations. Three sheep trails with altogether 12 calcareous grassland sites were chosen for the analysis of the tussock grass Bromus erectus, which is known to be the species with the highest rate of dispersal via sheep fleece. Each trail links two to four isolated populations. Allozymes were chosen as genetic markers. Six loci were used, five of which were polymorphic. While genetic variability within populations was found to be quite high (averaged h=0.352), only little between-population differentiation was measured (G_ST=5.5%). Despite this, the UPGMA-dendrogram of Nei's genetic distance shows genetic similarity relations largely congruent with the sheep herding trails. However, a (more) detailed comparison reveals several differences between genetic patterns and trail system. Hence, additional factors other than dispersal by sheep are regarded as being responsible for exchange of genes, and sheep herding is considered to have only minor importance for the genetic patterns of the investigated species. The comparison of Bromus erectus to species with the same life history traits (i.e. pollination by wind, a perennial life cycle, and autopolyploid constitution) shows similar values, thus providing further evidence for the relatively small contribution of dispersal via sheep fleece.