Improving sampling designs for measuring restoration in aquatic habitats

Restoration of degraded habitat is an increasingly important toll for management. Unfortunately, much of the emphasis has been on restoring large structural elements of habitat (e.g. planting vegetation,removing weeds), with little consideration about how well these activities restore ecologically functioning habitat. There has been considerable research in recent years into improving sampling designs and analytical techniques to measure the effects of environmental impacts taking into account the large spatial and temporal variability that occurs naturally in undisturbed habitats. In a similar manner to detection of impacts, restoration needs to be measured as an interaction between spatial and temporal components of variation against a variable background. Very few studies of restoration have explicitly addressed how best to do this. Neither have they attempted to assess the usefulness of some of these new techniques for measuring restoration. This review discusses some of the problems that need to be considered when measuring restoration and the potential value of some of these new methodologies. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of management practices on bumblebee densities in hedgerow and grassland habitats

Large-scale declines in pollinator species are a concern at present. Such declines have been attributed to a range of factors that act in tandem, rather than in isolation. Some of the most pervasive factors affecting pollinator populations are habitat loss and degradation, which results in the loss of floral resources, nesting sites and landscape connectivity. Intensification of agriculture and urbanisation are two major causes of such habitat alterations. Hedgerows and grasslands are two vital habitats for pollinators in European landscapes. When managed appropriately, these habitats may provide abundant floral resources and nesting opportunities, as well as connectivity between habitats in a fragmented landscape. This study examined the effects that management practices of hedgerows and grasslands may have on bumblebee species, an important group of wild pollinators. Bumblebee abundance was recorded using transect walks in managed and unmanaged sites, including both hedgerows and grasslands. Greater densities of bumblebees were found in unmanaged grasslands in comparison to managed grasslands. Unmanaged hedgerows were also found to have a greater density of bumblebees than managed hedgerows. These results indicate that sites which are less intensively managed provide a more suitable habitat for bumblebees. Therefore, our study underlines the importance of (a) enforcing restrictions on hedge-cutting, and (b) reducing the management intensity of grasslands to provide adequate habitat for pollinators.     

Estimating red deer abundance in a wide range of management situations in Mediterranean habitats

When human interventions interfere with the natural regulation of wildlife populations by favouring some species, overabundance can emerge. We evaluated different methods of estimating red deer abundance in a wide range of population densities from southern Spain. Distance sampling estimates were used as the reference method across 22 localities and were compared with two kilometric abundance indices (KAIs), four indices based on pellet group counts and two browsing indices (BWIs). The average red deer density estimated by distance sampling was 19.51±3.19 deer per 100 ha, showing a wide range across the study area (0.04–66.77). Distance sampling estimates correlated with the KAIs, pellet group-based index and the BWI. The agreement with distance sampling improved when groups were used instead of individuals in the KAIs, when the minimum pellet group size was fixed at 20 pellets in the dropping counts, and when only highly palatable species were used in the BWI. Thus, several direct and indirect methods can estimate red deer abundance in Mediterranean habitats from Southern Spain with appropriate modifications.     

Terrestrial small mammal diversity and abundance in central Benin: comparison between habitats,with conservation implications

We performed a terrestrial small mammal species inventory in the Agoua and Wari‐Maro forest reserves (Benin). Four localities were sampled, and in each locality, three habitats were surveyed: dense forest, open forest or woodland savannah and shrub savannah. This is the first comprehensive inventory for small mammals in central Benin. We captured 794 small mammals representing twenty species (six shrew species, fourteen rodent species). Three new species that need to be described were recorded. We observed a mixture of both true forest species and of species adapted to a wider range of habitats ranging from savannah to forest clearings. Species with either Sudanian or Guinea–Congolian affinities were recorded, as well as a new species endemic to Togo and Benin. This rich biodiversity underlines the urgent need for an effective protection of these forests. The Sudanian species Crocidura cf. foxi was more abundant in Wari‐Maro than in Agoua forest, while the Guineo–Congolian species Praomys misonnei and Hylomyscus sp were only captured in Agoua forest. These results are in agreement with the fact that these two forests belong to two distinct chorological zones.     

Structural comparison of a homologous neuron in gryllid and acridid insects

The fast extensor tibiae (FETi) motor neuron is responsible for exciting the extensor tibiae muscle to produce most of the force for jumping in acridids. Because of its relatively large size and crucial role in jumping, FETi has been studied in an ever-increasing number of orthopteran species. Here we describe the structure of the metathoracic FETi neuron in six species of acridids and in two species of gryllids. The morphology of FETi within the respective groups is essentially equivalent, but marked differences are apparent between acridid and gryllid FETis. There are similarities in the size and location of the cell body and the course of the neurite through the ganglion. Differences are found in the number of large branches, density of branching, and the volume of neuropil receiving branches. We propose that the gryllid FETi is an intermediate form between slow extensor tibiae motor neurons involved in walking and acridid fast extensor tibiae motor neurons specialized for jumping.     

Mapping functional traits: comparing abundance and presence-absence estimates at large spatial scales

Efforts to quantify the composition of biological communities increasingly focus on functional traits. The composition of communities in terms of traits can be summarized in several ways. Ecologists are beginning to map the geographic distribution of trait-based metrics from various sources of data, but the maps have not been tested against independent data. Using data for birds of the Western Hemisphere, we test for the first time the most commonly used method for mapping community trait composition - overlaying range maps, which assumes that the local abundance of a given species is unrelated to the traits in question - and three new methods that as well as the range maps include varying degrees of information about interspecific and geographic variation in abundance. For each method, and for four traits (body mass, generation length, migratory behaviour, diet) we calculated community-weighted mean of trait values, functional richness and functional divergence. The maps based on species ranges and limited abundance data were compared with independent data on community species composition from the American Christmas Bird Count (CBC) scheme coupled with data on traits. The correspondence with observed community composition at the CBC sites was mostly positive (62/73 correlations) but varied widely depending on the metric of community composition and method used (R(2): 5.6×10(-7) to 0.82, with a median of 0.12). Importantly, the commonly-used range-overlap method resulted in the best fit (21/22 correlations positive; R(2): 0.004 to 0.8, with a median of 0.33). Given the paucity of data on the local abundance of species, overlaying range maps appears to be the best available method for estimating patterns of community composition, but the poor fit for some metrics suggests that local abundance data are urgently needed to allow more accurate estimates of the composition of communities.     

The role of sampling effort,taxonomical resolution and abundance weight in multivariate comparison of stream dwelling caddisfly assemblages collected from riffle and pool habitats

We examined how the sample representativeness of a single assemblage and the separation of two assemblages can be improved by finding appropriate combinations of sampling effort, taxonomical resolution and abundance weight for stream dwelling caddisflies as model organisms. We found that these parameters strongly influenced the outcome of multivariate analyses both individually and when considered jointly. This is the first study to show that sample representativeness of an assemblage can decrease with increasing sampling effort. We assume that the turnover rate of the assemblage and the rarity of the species are responsible for this phenomenon. We found that the separation of two assemblages can be improved by increasing sampling effort and applying abundance data. Further, we observed that the effect of taxonomical resolution on the separation of ecological assemblages was highly context-dependent. Decreased taxonomical resolution, i.e. changing from species to genus or to family, did not decrease, or even more increased the separation of assemblages. In sum, this study demonstrates the importance of the careful selection of sampling, laboratory and data processing related factors (i.e. sampling effort, taxonomical resolution, abundance weight) in the multivariate comparison of assemblages.     

A comparison of sampling methods for bibionid larvae (Diptera: Bibionidae) in grassland

Three extraction methods were compared for the recovery of bibionid larvae from grassland soil samples. Only wet-sieving followed by flotation in a saturated salt solution yielded bibionids. No larvae were recovered either with modified Tullgren funnels or by slow immersion of soil cores into a saturated salt solution. The efficiency with which larval bibionid populations can be estimated is poor. Generally, smaller cores yielded more larvae per volume of soil. Most bibionids were found in the top 4 cm of soil. It is concluded that 10 cm diameter and 6–8 cm deep soil cores are an acceptable compromise between efficiency and sampling effort but sample size will largely be determined by the resources available for processing of samples.     

Estimating grizzly and black bear population abundance and trend in Banff National Park using noninvasive genetic sampling

We evaluated the potential of two noninvasive genetic sampling methods, hair traps and bear rub surveys, to estimate population abundance and trend of grizzly (Ursus arctos) and black bear (U. americanus) populations in Banff National Park, Alberta, Canada. Using Huggins closed population mark-recapture models, we obtained the first precise abundance estimates for grizzly bears (N=?73.5, 95% CI?=?64-94 in 2006; N=?50.4, 95% CI?=?49-59 in 2008) and black bears (N=?62.6, 95% CI?=?51-89 in 2006; N=?81.8, 95% CI?=?72-102 in 2008) in the Bow Valley. Hair traps had high detection rates for female grizzlies, and male and female black bears, but extremely low detection rates for male grizzlies. Conversely, bear rubs had high detection rates for male and female grizzlies, but low rates for black bears. We estimated realized population growth rates, lambda, for grizzly bear males (λ=?0.93, 95% CI?=?0.74-1.17) and females (λ=?0.90, 95% CI?=?0.67-1.20) using Pradel open population models with three years of bear rub data. Lambda estimates are supported by abundance estimates from combined hair trap/bear rub closed population models and are consistent with a system that is likely driven by high levels of human-caused mortality. Our results suggest that bear rub surveys would provide an efficient and powerful means to inventory and monitor grizzly bear populations in the Central Canadian Rocky Mountains.     

Stoat density, diet and survival compared between alpine grassland and beech forest habitats

In New Zealand, alpine grasslands occur above the treeline of beech forest. Historically stoat control paradigms in New Zealand?s montane natural areas have assumed alpine grassland is a marginal habitat that limits dispersal between beech forest stoat populations. We compared the summer-to-autumn (January?April) density, weight, diet and winter survival of stoats between these two habitatsduring years of low beech seedfall. Stoats were live-trapped, marked and released in alpine grassland and low-altitude beech forest in the Borland Valley, Fiordland National Park, during 2003 and 2004, and were caught and euthanased for necropsy in 2005. Stoat density was estimated using spatially explicit capture?recapture (SECR). The proportion of stoats marked in one year but recaptured in the next was used as a measure of ?observed survival?. Prey remains were identified from scats collected during 2003 and 2004 and stomachs from stoats killed in 2005. Stoat density was similar in both habitats over the two years, about one stoat per square kilometre. Observed survival from 2003?2004 was also similar, but survival from 2004?2005 was higher in alpine grassland than in beech forest. In 2003, male stoats were on average heavier in alpine grassland than in beech forest, although average weights were similar in the other years. Diet differed significantly between the two habitats, with stoats in alpine grasslands eating mainly ground weta (a large invertebrate) (72%) and hares (23%), while stoats in beech forest ate mainly birds (31%) and mice (19%). Collectively these results suggest that alpine grasslands are not a poor quality habitat for stoats. Traditionally it has been thought that stoats cannot survive on invertebrate prey alone. This research demonstrates that stoats relying largely on invertebrate prey can occur at similar densities and with equivalent survival to stoats relying on vertebrate prey.     

Distribution and abundance of fish in deep-sea coral habitats

Experimental fishing with long-lines and gillnets was conducted on the continental shelf off southwestern Norway between 150 and 350 m depth. Abundance and distribution of redfish (Sebastes marinus L., 1758), ling (Molva molva L., 1758), and tusk (Brosme brosme Ascanius, 1772) were quantified in Lophelia pertusa (L., 1758) coral reefs and in non-coral habitats. The largest catches of redfish were made with long-line fleets set in coral reef habitats. Ling and tusk were also most numerous in coral habitats, although not statistically significant. Fish caught in coral habitats tended to be larger in size than in non-coral habitats. The diet of redfish, tusk and ling included the same prey groups in all habitats, but they differed at the species level. Lophelia-reefs may provide a profitable feeding place for tusk. For the planktivorous Sebastes, on the other hand, their affinity to the reefs seems primarily to be related to the physical structure offered by the reefs.     

Phenology of Lygus lineolaris (Hemiptera: Miridae) in Minnesota June-bearing strawberries: comparison of sampling methods and habitats

Field studies were conducted in southeastern Minnesota from 2000 to 2002 to determine the phenology of Lygus lineolaris in various habitats and to compare yellow and white sticky traps as a sampling method for adult L. lineolaris. Strawberry fields were sampled for L. lineolaris adults using yellow sticky traps, and nymphs were sampled using the standard white pan beat method. Adult L. lineolaris abundance in alfalfa, an adjacent fence-row, and a wooded habitat were also compared. The nonlinear relationship between cumulative trap catch and cumulative degree-days was modeled with a two-parameter cumulative Weibull function to predict early-season adult capture using yellow sticky traps. Adult L. lineolaris were detected in bearing-year strawberries at the onset of vegetative growth in all years. Yellow sticky traps caught significantly higher densities of adult L. lineolaris than white sticky traps. The Weibull model predicted 50% capture at 10 DD (>12.4 degrees C), which corresponds to the vegetative strawberry growth stage. L. lineolaris nymphs were not detected until the blossom stage. Alfalfa harbored significantly higher densities of L. lineolaris than other habitats during early-season sampling (i.e., March-June). Late-season sampling (July-September) revealed significantly higher densities in bearing-year strawberries. These results suggest that monitoring at the onset of vegetative growth, using yellow sticky traps, will be an efficient method for detecting early L. lineolaris adult activity.     

Spider community responses to grassland restoration: balancing trade‐offs between abundance and diversity

Spiders (Araneae) play key roles in ecosystems, not only as common and abundant generalist predators, but also as major contributors to biodiversity in many areas. In addition, due to their short generation times and high mobility, spiders respond rapidly to small changes in their environment, potentially making them useful indicators for restoration monitoring. However, few studies have focused on spider responses to grassland restoration in the United States. We compared degraded, native, and restored grassland sites to examine how spider communities and habitat respond to arid grassland restoration. We also examined how responses varied with the age of the restoration project. Spider communities in native sites differed from those in restored and degraded sites in several ways: native sites had fewer spiders and a different community composition than degraded and restored sites. However, native and restored sites had more species than degraded sites. Chronosequence data showed trends for lower abundance, higher species richness, and changing community composition as restoration projects mature. Several habitat variables were closely linked to variation in spider communities including cover of invasive annual grasses, litter, and biological soil crusts. Our data suggest that spider and vegetation responses to grassland restoration efforts can be successful in the long term—with resulting communities becoming more similar to native ones—and that spiders are useful indictors of grassland restoration. Our results also suggest that restoration may involve balancing trade‐offs between ecosystem services, with potential losses in predatory control offset by increases in biodiversity with restoration effort.     

Competition between birds and mammals: A comparison of giving-up densities between crested larks and gerbils

We combined the concept of mechanisms of co-existence with the approach of giving-up densities to study inter-taxon competition between seed-eating birds and mammals. We measured feeding behaviour in food patches to define and study the guild of seed-eating vertebrates occupying sandy habitats at Bir Asluj, Negev Desert, Israel. Despite a large number of putatively granivorous rodents and birds at the site, two gerbil species (Allenbys gerbil, Gerbillus allenbyi, and the greater Egyptian gerbil, G. pyramidum) dominated nocturnal foraging, and a single bird species (crested lark, Galerida cristata) contributed all of the daytime foraging. We used giving-up densities to quantify foraging behaviour and foraging efficiencies. A low giving-up density demonstrates the ability of a forager to profitably harvest food at low abundances and to profitably utilize the foraging opportunities left behind by the less efficient forager. Gerbils had lower giving-up densities in the bush than open microhabitat, and lower giving-up densities in the semi-stabilized than stabilized sand habitats. Crested larks showed the opposite: lower giving-up densities in the open than bush, and on the stabilized than semi-stabilized sand habitats. Despite these patterns, gerbils had substantially lower giving-up densities than crested larks in both microhabitats, all sand habitats, and during each month. Several mechanisms may permit the crested lark to co-exist with the gerbils. Larks may be cream skimmers on the high spatial and temporal variability in seed abundances. Larks may rely on insects, fruit or smaller seeds. Or, larks may rely on adjacent rocky habitats.