Habitat Selection in a Rocky Landscape: Experimentally Decoupling the Influence of Retreat Site Attributes from That of Landscape Features

Organisms selecting retreat sites may evaluate not only the quality of the specific shelter, but also the proximity of that site to resources in the surrounding area. Distinguishing between habitat selection at these two spatial scales is complicated by co-variation among microhabitat factors (i.e., the attributes of individual retreat sites often correlate with their proximity to landscape features). Disentangling this co-variation may facilitate the restoration or conservation of threatened systems. To experimentally examine the role of landscape attributes in determining retreat-site quality for saxicolous ectotherms, we deployed 198 identical artificial rocks in open (sun-exposed) sites on sandstone outcrops in southeastern Australia, and recorded faunal usage of those retreat sites over the next 29 months. Several landscape-scale attributes were associated with occupancy of experimental rocks, but different features were important for different species. For example, endangered broad-headed snakes (Hoplocephalus bungaroides) preferred retreat sites close to cliff edges, flat rock spiders (Hemicloea major) preferred small outcrops, and velvet geckos (Oedura lesueurii) preferred rocks close to the cliff edge with higher-than-average sun exposure. Standardized retreat sites can provide robust experimental data on the effects of landscape-scale attributes on retreat site selection, revealing interspecific divergences among sympatric taxa that use similar habitats

Frequency of antimicrobial resistance among invasive and colonizing Group B Streptococcal isolates

BACKGROUND: Group B Streptococcus (GBS) remains susceptible to penicillin, however, resistance to second-line antimicrobials, clindamycin and erythromycin, has increased since 1996. We describe the age-specific antibiotic susceptibility profile and capsular type distribution among invasive and colonizing GBS strains. METHODS: We tested 486 invasive GBS isolates from individuals of all ages collected by a Wisconsin surveillance system between 1998 and 2002 and 167 colonizing strains collected from nonpregnant college students during 2001 in Michigan. Antimicrobial susceptibility testing was performed by disk diffusion or Etest and capsular typing was performed using DNA dot blot hybridization RESULTS: 20.0% (97/486) of invasive and 40.7% (68/167) of colonizing isolates were resistant to clindamycin (P < .001) and 24.5% (119/486) of invasive and 41.9% (70/167) of colonizing isolates were resistant to erythromycin (P < .001). Similarly, 19.8% (96/486) of invasive and 38.3% (64/167) of colonizing isolates were resistant to both antimicrobial agents (P < .001). 29.4% (5/17) of invasive isolates from persons 18–29 years of age and 24.3% (17/70) of invasive isolates from persons 30–49 years of age were resistant to clindamycin. Similarly, 35.3% (6/17) of invasive isolates from persons 18–29 years of age and 31.4% (22/70) of invasive isolates from persons 30–49 years of age were resistant to erythromycin. 34.7% (26/75) of invasive isolates from persons < 1 year of age were capsular type Ia, whereas capsular type V predominated among isolates from adults. CONCLUSION: Clindamycin and erythromycin resistance rates were high among isolates colonizing nonpregnant college students and invasive GBS isolates, particularly among the colonizing isolates. Susceptibility profiles were similar by age although the proportion of clindamycin and erythromycin resistance among invasive isolates was highest among persons 18–49 years of age. Increasing antimicrobial resistance has implications for GBS disease treatment and intrapartum prophylaxis among penicillin intolerant patients

Group B streptococcus serotype prevalence in reproductive-age women at a tertiary care military medical center relative to global serotype distribution

<p>Abstract</p> <p>Background</p> <p>Group B <it>Streptococcus </it>(GBS) serotype (Ia, Ib, II-IX) correlates with pathogen virulence and clinical prognosis. Epidemiological studies of seroprevalence are an important metric for determining the proportion of serotypes in a given population. The purpose of this study was to evaluate the prevalence of individual GBS serotypes at Madigan Healthcare System (Madigan), the largest military tertiary healthcare facility in the Pacific Northwestern United States, and to compare seroprevalences with international locations.</p> <p>Methods</p> <p>To determine serotype distribution at Madigan, we obtained GBS isolates from standard-of-care anogenital swabs from 207 women of indeterminate gravidity between ages 18-40 during a five month interval. Serotype was determined using a recently described molecular method of polymerase chain reaction by capsular polysaccharide synthesis (cps) genes associated with pathogen virulence.</p> <p>Results</p> <p>Serotypes Ia, III, and V were the most prevalent (28%, 27%, and 17%, respectively). A systematic review of global GBS seroprevalence, meta-analysis, and statistical comparison revealed strikingly similar serodistibution at Madigan relative to civilian-sector populations in Canada and the United States. Serotype Ia was the only serotype consistently higher in North American populations relative to other geographic regions (p < 0.005). The number of non-typeable isolates was significantly lower in the study (p < 0.005).</p> <p>Conclusion</p> <p>This study establishes PCR-based serotyping as a viable strategy for GBS epidemiological surveillance. Our results suggest that GBS seroprevalence remains stable in North America over the past two decades.</p

Context-dependent avoidance of predatory centipedes by nocturnal geckos (Oedura lesueurii)

Most research on the anti-predator behaviour of vertebrate prey has focused on their responses to vertebrate predators. Nonetheless, invertebrates are abundant predators in terrestrial ecosystems, and some invertebrates (e.g., centipedes, spiders) attack and consume vertebrates. We used a combination of field data and laboratory experiments to determine whether a predatory centipede (Scolopendridae: Cormocephalus sp.) influences habitat selection by the nocturnal rock-dwelling velvet gecko, Oedura lesueurii. In the field, centipedes and geckos were syntopic, and sheltered beneath rocks with similar physical dimensions, thermal regimes and degree of sun exposure. Nonetheless, geckos rarely shared rocks with centipedes in the field. In laboratory trials, both geckos and centipedes selected shelters with narrow rather than wide crevices. The presence of a centipede modified habitat selection by juvenile geckos, which preferred wide crevices without centipedes to narrow crevices containing centipedes. In contrast, adult geckos continued to select narrow crevices even if these contained centipedes. When we added centipedes to narrow crevices beneath small and large rocks occupied by geckos, both juvenile and adult geckos exited the crevice (especially if it was under a small rather than large rock). Our results show that centipedes influence habitat selection by velvet geckos, and demonstrate that anti-predator behaviours of geckos are both size- and context-dependent. Ontogenetic shifts in behaviour and habitat selection by vertebrates in response to invertebrate predators may be widespread

Three-dimensional crevice structure affects retreat site selection by reptiles

When selecting retreat sites, rock-dwelling animals assess thermal and hydric properties of the rocks under which they shelter. Another obvious, but harder to measure, factor that may affect retreat site selection is the size and structure of the three-dimensional crevice beneath the rock. We developed a novel technique to quantify crevice structure beneath rocks and compared crevices used by snakes and lizards with unused crevices. Multiple attributes of crevice structure such as the height of the crevice above the substrate, the area of the crevice suitable for fitting the entire body of the animal, the degree of closure of the crevice and the amount of fragmentation within the crevice affected the suitability of a crevice as a retreat site. Therefore, crevice structural attributes, not simply size and thickness of the overlying rock, may be important factors driving retreat site selection by ectotherms. We also found that crevice structure directly alters thermal regimes, and may be more important than rock thickness in this respect. Understanding the characteristics of the space actually occupied by animals can yield a greater understanding of habitat selection, and our novel technique for quantifying crevice geometry should be readily transferable to other systems

Details of generalized linear mixed models comparing the attributes of used <i>versus</i> unused artificial rocks by species.

<p>Sample sizes, average parameter estimates, standard errors of these estimates, and sum of Akaike weights (w_i) for explanatory variables derived for all combinations of the generalized linear models comparing the attributes of used artificial rocks <i>versus</i> those not known to have been used by seven different wildlife species on sandstone outcrops in south-eastern Australia. Boldface values have a high w_i value, indicating high importance.</p

Details of generalized linear mixed models predicting the frequency of use of artificial rocks by species.

<p>Average parameter estimates, standard errors of these estimates, and sum of Akaike weights (w_i) for explanatory variables derived for all combinations of the generalized linear models predicting the frequency of usage of artificial rocks by six different wildlife species on sandstone outcrops in south-eastern Australia. Rocks never recorded as being used by a given species are omitted from these analyses. Bold values have a high w_i value, indicating high importance.</p

Preliminary producer data synthesis, 1970 comprehensive network sites

August 1972.On cover: Grassland Biome, Ecosystem analysis studies, U.S. International Biological Program.Includes bibliographical references