The influence of habitat provisioning: use of earthworm burrows by the terrestrial salamander, Plethodon cinereus

Studies examining the influence of habitat provisioning by one species on the behavior of other species can provide key insights regarding impacts of ecosystem engineers on the availability of resources to other species. More specifically, an organism’s use of additional habitat provided by ecosystem engineers may affect the interpretation of observational or demographic data. We chose to examine the possible influence of earthworms, as ecosystem engineers, on the behavior of terrestrial salamanders, common forest vertebrates in North America. We conducted two experiments in microcosms to examine whether the earthworm Lumbricus terrestris acted as an ecosystem engineer by providing additional habitat (burrows) for Plethodon cinereus, a common woodland salamander. We also examined whether the behavioral changes of the non-burrowing, fossorial P. cinereus differed across age classes. Adults and juveniles responded similarly, with both adults and juveniles found under cover objects more often when earthworms were absent and using earthworm burrows when available. Our field data supported our experimental data in that greater numbers of earthworms on field plots were associated with a lower proportion of cover objects being occupied by salamanders (i.e., salamanders were likely underground). We found no differences in the response of adults and juveniles to the presence of earthworms. By providing underground habitat for a common terrestrial amphibian, the presence of earthworms may impact demographic studies on salamanders and conclusions drawn from those studies regarding aboveground faunal communities in eastern North America.     

Habitat preferences of the threatened Black-eared Wheatear Oenanthe hispanica in southern Italy

Capsule We analysed habitat preferences of Black-eared Wheatear Oenanthe hispanica of the eastern subspecies (O. hispanica melanoleuca) in South Italy, considering 1-ha (coinciding with territory size) square plots (49 occupied and 49 unoccupied). We used multi-adaptive regression splines to model habitat preferences. Black-eared Wheatear occurrence was positively associated with three factors: aspect (a SE orientation was preferred), cover of grazed grassland and cover of bare ground. Species conservation should be based on the maintenance of grazed grasslands, especially on SE-facing slopes, and including at least 2500 m² of bare ground per ha.     

Habitat alteration increases invasive fire ant abundance to the detriment of amphibians and reptiles

Altered habitats have been suggested to facilitate red imported fire ant (Solenopsis invicta) colonization and dispersal, possibly compounding effects of habitat alteration on native wildlife. In this study, we compared colonization intensity of wood cover boards by S. invicta among four forest management treatments in South Carolina, USA: an unharvested control (>30 years old); a partially thinned stand; a clearcut with coarse woody debris retained; and a clearcut with coarse woody debris removed. Additionally, we compared dehydration rates and survival of recently metamorphosed salamanders (marbled salamanders, Ambystoma opacum, and mole salamanders, A. talpoideum) among treatments. We found that the number of wood cover boards colonized by S. invicta differed significantly among treatments, being lowest in the unharvested forest treatments and increasing with the degree of habitat alteration. Salamanders that were maintained in experimental field enclosures to study water loss were unexpectedly subjected to high levels of S. invicta predation that differed among forest treatments. All known predation by S. invicta was restricted to salamanders in clearcuts. The amount of vegetative ground cover was inversely related to the likelihood of S. invicta predation of salamanders. Our results show that S. invicta abundance increases with habitat disturbance and that this increased abundance has negative consequences for amphibians that remain in altered habitats. Our findings also suggest that the presence of invasive S. invicta may compromise the utility of cover boards and other techniques commonly used in herpetological studies in the Southeast.     

Is local distribution of the epiphytic lichen <Emphasis Type="Italic">Lobaria pulmonaria</Emphasis> limited by dispersal capacity or habitat quality?

By surveying and re-surveying 12 forest sites in southern Sweden for the epiphytic lichen Lobaria pulmonaria with a 9-year interval, and measuring tree-related habitat quality variables, we have investigated whether the local distribution of the lichen is limited by poor dispersal capacity or by habitat quality. Dispersal distances were measured indirectly as the distances between colonised trees and the nearest trees occupied by L. pulmonaria in both 1992 and 2001. To compare habitat quality between trees occupied by L. pulmonaria and neighbouring control trees, we recorded tree species and measured age and growth rate of trees, light conditions, bark structure and bryophyte cover. The estimated mean dispersal distance was 35 m, with a recorded maximum of 75 m. Occupied trees were larger and had a larger cover of bryophytes than unoccupied trees of similar size. The results indicate that dispersal capacity probably is the most important factor in limiting the local distribution of L. pulmonaria, but habitat-quality factors may be important on a smaller spatial scale.     

Behavioral interactions between salamanders and centipedes: competition in divergent taxa

Red-backed salamanders, Plethodon cinereus, use territorialadvertisement in the form of agonistic displays and pheromonalscent marking as a mechanism for intraspecific interferencecompetition. Although ecological and behavioral interactionsamong species of salamanders have been well studied, littleis known about the interactions between territorial P. cinereusand other ecologically similar species, such as large predatoryinvertebrates. Our field data indicate that P. cinereus anda large syntopic centipede, Scolopocryptops sexspinosus, exhibitnegative spatial associations in natural habitats, possiblyindicating interspecific territoriality. Only seven instancesof salamander/centipede co-occurrence were recorded from a fieldsample of 247 occupied cover objects. Cover object size waspositively correlated with salamander SVL (tip of the snoutto the anterior end of the cloaca), but there was no correlationof cover object size to centipede length. Data on the abilityof P. cinereus to differentiate among chemicals on the substratesuggest that visual cues are not necessary to elicit a territorialresponse from intruding salamanders. Although in laboratorytrials salamanders behaved similarly toward intruders of bothspecies, biting was directed only toward centipedes. Salamandersspent significantly more time approaching centipedes than theydid approaching other salamanders. Approach behavior was oftenassociated with nose tapping and may be an investigative, ratherthan aggressive, behavior. We suggest that territorial P. cinereusrespond similarly to intruding salamanders and centipedes, butthat they escalate more readily to biting centipedes becauseS. sexspinosus is sightless and thus unable to respond to visualsignals.     

Characteristics of the breeding habitat of Endangered Kirtland's Warblers on a Canadian Military Installation

Kirtland's Warblers (Setophaga kirtlandii) are an endangered species with specialized habitat requirements, and the only documented nesting location in Canada is an Army installation. From 2007 to 2010, I compared habitat characteristics of sites occupied and not occupied by Kirtland's Warblers at Garrison Petawawa located ～200 km northwest of Ottawa, Ontario. Sites occupied by Kirtland's Warblers (N = 11) had greater percent cover of low sweet blueberry (Vaccinium angustifolium; 31.2%), coral lichen (Cladina stellaris; 0.4%), reindeer lichen (Cladonia rangiferina; 8.3%), and wavy‐leaved moss (Dicranum polysetum; 4.3%) than unoccupied sites (N = 6). I found no difference in tree species composition between sites, with jack pine (Pinus banksiana), white pine (Pinus strobus), red pine (Pinus resinosa), poplar (Populus tremuloides), and red maple (Acer rubra) present in both used and unused sites. Forest stands occupied by Kirtland's Warblers were significantly younger (< 20 yr old) than unoccupied sites, and most occupied sites were within former fire zones and sites where jack pines had been planted. Thus, breeding habitat of Kirtland's Warblers in Canada consisted of young pine trees, with more red pine than in their breeding habitat in Michigan, and ground cover including blueberry, lichens, and mosses. These results suggest that Kirtland's Warblers may be less selective in their habitat requirements than previously thought, and should provide guidance for recovery groups and regulatory agencies in accurately delineating suitable habitat for these warblers in Canada.     

Territorial defence of space and feeding sites by a plethodontid salamander

Two series of experiments were conducted, one in field enclosures and another in the laboratory, to test the hypothesis that the salamander Desmognathus monticola (family Plethodontidae) defends its refuges and feeding sites against conspecific intruders. When two identical cover sites were provided as refuges in the laboratory, residents and intruders occupied separate cover sites significantly more often than the same sites. Residents did not, however, show strong preference for the same site, nor did they consistently defend a specific site. When food supplements were provided consistently at the same cover sites in field enclosures, resident D. monticola occupied and defended the feeding sites significantly more frequently against intruders than the non-feeding cover sites. Individuals not receiving food supplements also excluded intruders from the occupied cover sites but did not defend a specific cover site. Residents in enclosures where no food supplements were provided were significantly more active at night, outside cover sites, than residents receiving food supplements. Individual D. monticola exhibit territoriality by excluding intruders from the refuges they occupy. Providing food supplements increases the site specificity of individuals and decreases the amount of time spent in nocturnal activity.     

Habitat as a potential factor limiting the recovery of a population of nocturnal seabirds

We asked whether the lack of a population response by ancient murrelets (Synthliboramphus antiquus) to eradication of rats (Rattus spp.) at Langara Island could be due to a change in vegetative cover. We quantified ancient murrelet habitat associations on 12 islands and assessed changes in vegetation at Langara Island between 1981 and 2007. We found that ancient murrelets exhibit a high degree of flexibility in their use of available breeding habitats, and we noted no changes over time. Thus, recovery of ancient murrelets at Langara Island is unlikely to be limited by habitat quality. We propose artificial social attraction as a method to speed recovery. © 2011 The Wildlife Society.     

Estimating Carrying Capacity for Sea Otters in British Columbia

ABSTRACT We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km² and 2.53 otters/km² for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI = 3,337–7,104; BC model: 4,883, 95% CI = 3,223–6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km²) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI = 9,790–20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI = 34,264–73,489)—a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.     

The effects of conspecifics on burrow selection in juvenile spotted salamanders (<Emphasis Type="Italic">Ambystoma maculatum)</Emphasis>

Spotted salamanders (Ambystoma maculatum) are pond-breeding amphibians that disperse into terrestrial habitat from natal wetlands after undergoing metamorphosis, relying on small-mammal burrows and coarse woody debris for refugia. The effect of conspecifics on burrow use in juvenile salamanders is poorly understood. Determining how the presence of conspecifics influences the settlement decisions of juvenile salamanders can increase our understanding of amphibian dispersal and our ability to predict population dynamics. We conducted behavioral laboratory trials using 58 recently metamorphosed salamanders to examine how salamanders selected burrows in the presence of conspecifics. Salamanders were more likely to settle in a burrow that was occupied by a conspecific versus an unoccupied burrow. Our results indicate that juvenile salamanders may show conspecific attraction and/or trailing behavior during the dispersal phase.     

Developing landscape habitat models for rare amphibians with small geographic ranges: a case study of Siskiyou Mountains salamanders in the western USA

To advance the development of conservation planning for rare species with small geographic ranges, we determined habitat associations of Siskiyou Mountains salamanders (Plethodon stormi) and developed habitat suitability models at fine (10 ha), medium (40 ha), and broad (202 ha) spatial scales using available Geographic Information Systems data and logistic regression analysis with an information theoretic approach. Across spatial scales, there was very little support for models with structural habitat features, such as tree canopy cover and conifer diameter. Model-averaged 95% confidence intervals for regression coefficients and associated odds ratios indicated that the occurrence of Siskiyou Mountains salamanders was positively associated with rocky soils and Pacific madrone (Abutus menziesii) and negatively associated with elevation and white fir (Abies concolor); these associations were consistent across 3 spatial scales. The occurrence of this species also was positively associated with hardwood density at the medium spatial scale. Odds ratios projected that a 10% decrease in white fir abundance would increase the odds of salamander occurrence 3.02–4.47 times, depending on spatial scale. We selected the model with rocky soils, white fir, and Oregon white oak (Quercus garryana) as the best model across 3 spatial scales and created habitat suitability maps for Siskiyou Mountains salamanders by projecting habitat suitability scores across the landscape. Our habitat suitability models and maps are applicable to selection of priority conservation areas for Siskiyou Mountains salamanders, and our approach can be easily adapted to conservation of other rare species in any geographical location.     

Aspects of habitat selection in the mosquitofish gambusia affinis

Laboratory experiments were performed to determine behavioral preferences of Gambusia affinis for habitat variables in partitioned aquaria. The fish preferred calm water, dark-colored substrates and subsurface vegetation providing lateral concealment. Floating cover, which obstructed access to the surface, was avoided. Lack of preference for real over plastic plant cover indicates that visual rather than chemical cues are involved. These laboratory preferences correspond to the reported microhabitat distribution of G. affinis in nature and indicate the presence of an active habitat preference, as opposed to passive habitat correlation, in this species. Species-specific habitat preferences, which may be narrower where a species occurs sympatrically with its congeners, probably form part of a reproductive isolating mechanism.     

Burrow densities and nest site preferences of petrels (Procellariidae) at the Prince Edwards Islands

Summary The nest-site preferences of six burrowing petrel species, Salvin's prion Pachyptila vittata salvini, blue petrel Halobaena caerulea, great-winged petrel Pterodroma macroptera, Kerguelen petrel Pterodroma brevirostris, soft-plumaged petrel Pterodroma mollis and white-chinned petrel Procellaria aequinoctialis, in the northeastern part of Marion Island (Prince Edward Island group, southern Indian Ocean) were analyzed by step-wise multiple regression. The nest-site characteristics measured were slope angle, soil depth and moisture content, percentage cover by stones or boulders and percentage cover by each of seven major plant species. The major nest-site preferences were: exposed areas with shallow soil (Salvin's prion); steep coastal slopes (blue petrel); sheltered well-drained slopes with deep soil (great-winged petrels); wet areas along drainage lines (Kerguelen petrel); steep slopes (soft-plumaged petrel); and areas with deep soil (white-chinned petrel). Similar species showed no significant avoidance of nest sites where there were burrows of potential competitors but did tend to nest spread out over different habitats. Burrow densities were determined in six habitat and seven vegetation types. Salvin's prion was the most abundant species (81% of burrows, with a maximum density of 279 burrows ha^-1) and used both burrows and natural cavities for nesting. For all species combined, burrow densities at Marion Island were lower than in comparable habitats and vegetation types at neighbouring Prince Edward Island. Depredation by feral house cats Felis catus, absent from Prince Edward Island, is assumed to be largely responsible for this difference.     

Effects of Timber Management on Pond-Breeding Salamanders

Abstract: Pond-breeding salamanders spend most of their lives in forested habitat surrounding the vernal pools where they breed. Timber harvesting has been demonstrated to have negative impacts on salamander populations due to changes in soil temperature, soil compaction, and general degradation of habitat. However, little is known about how long it takes for harvested forest habitat to once again become suitable for salamanders. Questions also remain as to whether salamanders will use an area that has been harvested in recent years if an older intact forest area is available. We used drift fences and pitfall traps to capture adult spotted salamanders (Ambystoma maculatum) and marbled salamanders (A. opacum) migrating to 3 vernal ponds during their breeding seasons. The study area contained tracts of forest that were clear-cut 11–12 years prior to the study. All 3 ponds were surrounded by areas of clear-cut and intact forest and drift fences were placed in both habitat types. Similar numbers of spotted salamanders entered the ponds from clear-cut and intact forest areas. The number of marbled salamanders migrating to the ponds did not differ between areas of clear-cut and intact forest. These results suggest that clear-cut habitats may become suitable for adult pond-breeding salamanders after a relatively short regeneration period.     

Habitat selection by two streamside plethodontid salamanders

Summary A series of experiments was conducted to test the hypothesis that habitat selection by the salamanders Desmognathus monticola and Desmognathus quadramaculatus is influenced differently by interspecific interference than by intraspecific interference. Individuals of neither species were influenced differently by the presence of heterospecifics than by the presence of conspecifics in their activity away from cover sites, in selection of different substrate moisture levels, in selection of different substrate textures, nor in selection of microhabitats relative to the streambed. Both species generally selected substrates with the highest moisture and the coarsest texture. Selection of different cover sizes by D. monticola depended on microhabitat, with larger rocks being selected most frequently when salamanders were farther from the streambed. D. quadramaculatus was seldom found away from the streambed and did not discriminate among the cover sizes available. The strong affinity of D. quadramaculatus for streambed microhabitat, compared with the much more variable microhabitat selection of D. monticola, resulted in spatial separation of individuals of the two species most of the time. Results of this study do not support the hypothesis that interspecific inference is more important than intraspecific interference in the microhabitat distributions of D. monticola and D. quadramaculatus.     

Habitat structure and predators: choices and consequences for rodent habitat specialists and generalists

Summary Both habitat structure and risk of predation are thought to influence rodent community composition in different habitats, but experiments on the degree to which these factors determine the use of habitat by rodents are lacking. I sought to discover (1) if cover density altered habitat choice and (2) if cover density affected the vulnerability to predators of two rodents, a habitat specialist and a habitat generalist. In laboratory experiments, the habitat specialist, the red-backed vole (Clethrionomys gapperi), preferred greater densities of both vertical (wall) and horizontal (ceiling) cover. The habitat generalist, the deer mouse (Peromyscus maniculatus), also preferred greater densities of vertical and horizontal cover, but its preferences were weaker and more inconsistent than those of C. gapperi In tests of vulnerability to domestic ferrets, C. gapperi were more vulnerable in arenas with less vertical cover, while P. maniculatus did not differ in vulnerability between the two vertical cover densities used. Vulnerability to predators in differing densities of horizontal cover was not tested because of the reduced differences in preference for this cover type between the rodent species. Risk of predation is one explanation for C. gapper's inherent preference for denser cover.     

Factors influencing patch occupancy and within‐patch habitat use in an apparently stable population of Willow Tits Poecile montanus kleinschmidti in Britain

Capsule Birds selected younger woodland patches with fewer conifers and higher soil moisture content; within these patches, they selected areas with higher vegetation cover at 2–4 m, and less bracken.

Aims For an apparently stable population, to investigate habitat differences between occupied and unoccupied woodland patches and habitat selection within occupied woodlands.

Methods We surveyed woodland patches for breeding Willow Tits in April 2006 in an area with an apparently stable population. Habitat was measured at points spread throughout each woodland patch and at points where Willow Tits were located. We compared habitat between occupied and unoccupied sites. In addition, within occupied sites, we examined habitat differences between Willow Tit locations and the points spread throughout the wood.

Results We surveyed 65 woodland patches, of which 29 were occupied. Willow Tits were more likely to be found in deciduous woodland that was younger and had higher levels of soil moisture. Probability of occupancy fell from 60% for woods aged 20–25 years to only around 15–30% for woods aged over 80 years. Within occupied woods, Willow Tits were more likely to be found in areas with more vegetation cover at the 2–4 m level and in areas with less bracken.

Conclusions Habitat management for Willow Tits should involve provision of young woodland patches with moist soils. Changes to the age structure and/or the soil moisture content of woods may be implicated in the dramatic decline of Willow Tits in Britain.     

The effect of elevation and habitat cover on nest box occupancy and diet composition of Boreal Owls Aegolius funereus

Capsule: Diet composition of Boreal Owls Aegolius funereus was not affected by habitat cover, but it changed along the elevational gradient.

Aims: To assess the effect of elevation and habitat cover on nest box occupancy and diet composition of a central European population of Boreal Owls.

Methods: A Boreal Owl population was studied in the ?umava Mountains, Czech Republic, at elevations from 500 to 1300?m above sea level (asl), during 1984–2005.

Results: Boreal Owls occupied more frequently nest boxes above 600?m asl, but they did not clearly prefer any elevational band. Habitat cover did not affect the number of nesting attempts. There was also no relationship between habitat cover and diet composition. However, diet composition significantly changed along the elevational gradient. In particular, the proportion of alternative prey of Boreal Owls, i.e. birds and shrews Sorex sp., rose with increasing elevation. The proportion of voles Myodes and mice Apodemus in the diet decreased with increasing elevation. Among bird prey, the proportion of finches Fringillidae positively correlated with elevation.

Conclusions: Central European Boreal Owls did not show a clear preference for any habitat cover or elevational band, but the quality of the owls’ diet significantly decreased with increasing elevation.     

Lack of habitat segregation and no interspecific territoriality in three syntopic cryptic species of the golden‐spectacled warblers Phylloscopus (Seicercus) burkii complex

It is widely accepted that exploitative competition prevents the coexistence of any two or more closely‐related species unless differences exists in their ecological niches and resource use. In sibling bird species, exploitative competition is reduced mainly by spatial segregation of competing species. Spatial segregation can be achieved in two basic ways: by using different habitats or microhabitats that each species is predominately exploiting, or by interspecific territoriality. To our knowledge, either habitat segregation or interspecific territoriality or both have been found in all dyads and groups of sympartic sibling bird species studied so far. In this study, we investigated the coexistence of three cryptic sibling species of the golden‐spectacled warblers Phylloscopus burkii complex in Hunan Province, China: Ph. tephrocephalus, Ph. omeiensis and Ph. valentini. We analyzed their habitat preferences, and spatial interrelations between the species. In order to analyze either presence or absence of interspecific territoriality, we additionally performed con‐ and heterospecific playback experiments. Contrary to expectations, we found no evidences for either habitat segregation or interspecific territoriality in these three species.     

Experimentally induced helper dispersal in colonially breeding cooperative cichlids

The ‘benefits of philopatry’ hypothesis states that helpers in cooperatively breeding species derive higher benefits from remaining home, instead of dispersing and attempting to breed independently. We tested experimentally whether dispersal options influence dispersal propensity in the cooperatively breeding Lake Tanganyika cichlids Neolamprologus pulcher and N. savoryi. Cooperative groups of these fishes breed in densely packed colonies, surrounded by unoccupied, but apparently suitable breeding habitat. Breeding inside colonies and living in groups seems to benefit individuals, for example by early detection and deterrence of predators. We show that despite a slight preference of both species for habitat with a higher stone cover, 40% of the preferred habitat remained unoccupied. On average, the colonies contained a higher number of (1) predators of adults, juveniles and eggs, (2) shelter competitors, and (3) other species including potential food competitors, compared to the outside colony habitat. Apparently, habitat differences cannot explain why these cichlids breed in colonies. Accordingly, dispersal may not be limited by a lack of suitable breeding shelters, but by the relatively higher risk of establishing an outside- compared to a within-colony breeding territory. To test whether cichlids prefer within- to outside-colony breeding territories, we provided breeding shelters inside the colony and at the colony edge and studied helper dispersal. As expected, significantly more shelters were occupied within the colony compared to the edge. New breeding pairs with several helpers occupied these shelters. We conclude that although breeding habitat is plentiful outside the colonies, helpers delay dispersal to obtain a higher quality breeding position within the group or colony eventually, or they disperse in groups. Our results suggest that (1) group augmentation and Allee effects are generally important for dispersal decisions in cooperatively breeding cichlids, consistent with the ‘benefits of philopatry hypothesis’, and (2) habitat saturation cannot fully explain delayed dispersal in these species.