Burrow Density Research Articles

Effect of crab bioturbation on organic matter processing in South West Atlantic intertidal sediments

Organic matter (OM) remineralization plays a key role in controlling the biogeochemistry of marine sediments. Through their burrowing activities, bioturbating macrofauna not only induces physical, chemical and biological modifications, which can affect microbial communities responsible for organic matter remineralization, but it could also directly affect the distribution and bioavailability of sedimentary organic matter. Through in situ experiments manipulating crab and burrow density in intertidal soft-bottoms, we assessed if crab-bioturbation affects benthic metabolism, and the amount, distribution, and bioavailability of sedimentary OM. Crab-bioturbation enhanced overall benthic metabolism and benthic flux of dissolved OM toward the water column at both mudflat and saltmarsh zones. Moreover, our results revealed that bioturbation also changes the quality, bioavailability and distribution of sedimentary OM in mudflats and saltmarshes. Overall, bioturbation enhanced the proportion of labile organic carbon of bioturbated sediments and homogenized the sediment column in terms of their proportion of labile organic carbon. However, crabs also generated biogenic structures (e.g., mounds) that could promote spatial heterogeneity of high nutritional-value OM. Bioturbation-induced changes on benthic metabolism and on OM availability would result in a reduction of the storage capacity of carbon in our intertidal systems. Previous works indicated that crab-burrows trap detritus and OM-rich sediments. Our results suggest that detritus are efficiently remineralized at bioturbated sediment, and finally they are quickly exported to the water column as CO2 and DOC. Thus, crabs are modifying the OM processing at intertidal soft bottoms, and the ways in which carbon is exported to coastal waters.

Resources and their distribution can influence social behaviour at translocation sites: Lessons from a lizard

In a translocation programme, social interactions among released individuals can influence the tendency for the individuals to remain at the site where they have been released. Dispersal away from the region of release may reduce the success of a translocation because dispersing individuals may move into less suitable habitat, or become separated from potential reproductive partners. In soft releases, where individuals are confined together for periods of time at the release site, before ultimate release, social interactions among the confined individuals may promote subsequent dispersal. In this study we investigated how variation in the abundance and distribution of a fundamental habitat resource, refuge burrows, influenced behaviour and possible subsequent dispersal of newly released individuals of the endangered Australian pygmy bluetongue lizard, Tiliqua adelaidensis, in simulations of translocation releases. Our aim was to determine if there was an optimal distribution of burrow resources that would minimise behaviours likely to lead to dispersal from the release site. There were more lizard movement around burrows 3.73 (SE 0.02) and fewer burrow changes 0.06 (SE 0.006) in low burrow densities than in high burrow densities (1.88 (SE0.02) movements; 0.50 (SE 0.008) burrow changes per day). When lizards were released in burrows near to each other (50cm) they changed burrows more often (0.97 (SE 0.01)) and had more agonistic interactions (0.04 (SE 0.004)) than when released in burrows further apart (150cm; 0.22 (SE 0.009) burrow changes; 0.003 (SE 0.001) agonistic interactions). These results suggest changes in behaviour can be induced by altering the way resources are distributed at a release site. We suggest that understanding the social organisation of any endangered species, and whether it can be manipulated, will be an important component of planning a translocation release programme.

Differences in burrow morphology of crabs between Spartina alterniflora marsh and mangrove habitats

Density and morphology of crab burrows were compared using resin casts between exotic Spartina alterniflora marsh (SPA) and four mangrove habitats (Avicennia marina forest, AM; Kandelia obovata forest, KO; Aegiceras corniculatum forest, AC; Mudflat, MF) at a subtropical mangrove estuary, Yunxiao, China. Five burrow-morphological parameters (density, opening diameter, depth, branching and total burrow volume per m2) were measured. The results showed that there were significant differences in the morphology (depth and volume) of crab burrows between SPA and mangrove habitats. The depth (ANOVA, d.f.=27, F=24.212, P=0.000) and total burrow volume (ANOVA, d.f.=23, F=3.666, P=0.022) per m2 in SPA were significantly lower than those in the other four mangrove habitats. Correlation analysis indicated significant negative correlation between burrow depth and root density. We concluded that over-dense roots and subterranean stems of Spartina alterniflora impeded crabs excavating burrows extensively, both in the vertical and horizontal directions. Consequently, the invasion of Spartina alterniflora weakened the ecosystem engineering effects of mangrove crabs. The burrows in KO and AM had significantly higher burrow complexity than those in the other three habitats. We speculated that mangrove root was the main environmental variable resulting in the varied complexity of crab burrows. Higher root density or lower root density both impede crabs constructing complex burrows, while intermediate root density contributes to the development of higher borrow complexity.

Bionomic aspects of Prorachias bristowei (Araneae: Mygalomorphae: Nemesiidae): burrow density and shape, food items, body size and reproduction

A population of Prorachias bristowei Mello Leitão 1924, a monotypic trapdoor spider, was studied in earthen road banks in southeastern Brazil. We assessed burrow densities, depths and widths, morphometric measures of spider bodies and recorded life history traits. Most burrows belonged to intermediate juveniles, followed by adults and a few juveniles. Egg sacs (mean of 131 eggs) and newly hatched spiderlings received parental care within the maternal burrow. Entrance diameters and burrow depths were significantly correlated with cephalothorax width and length, the length of the first leg and length of chelicera and number of eggs. Food items were Isopoda, Coleoptera, Hymenoptera and Ensifera. The clumped behavior and low dispersal ability can make the spiders vulnerable to anthropogenic modifications of their habitats.

Burrowing activity of the invasive red swamp crayfish, Procambarus clarkii, in fishponds of La Brenne (France)

In 2007, the invasive crayfish Procambarus clarkii (Girard 1852) was identified for the first time in the “Parc Naturel Régional de la Brenne” (Indre department, Centre region, France). Ten infestation sites were found in the park, with 62 fishponds colonised. To better understand how the fishponds could be affected, and changes in invaded ponds, we followed crayfish burrowing activity in recently drained fishponds in two areas. Weekly investigations of burrowing activity by analysing their density, occupation and location with respect to the banks, and micro-habitat features were carried out for 2 months in spring. Burrow densities of 1.16 and 1.05 burrows m–2 were found at Le Terrier Blanc and Coudreau 3 respectively. Procambarus clarkii sought humid soil in a dry pond and preferred burrowing on silt substrates. While no statistical differences were found between sites, some differences were observed among weeks independently of the sites. The mean mouth diameter of burrows in the two sites was 5.7 cm (SD = 2.17, n = 214; min. value: 1.2 cm; max. value: 14 cm). Notwithstanding the situation in the last weeks of the study (when most chimneys were built), there was a certain turnover between open and plugged burrows, and in occupancy. Given the scale and duration of the study and the number of fishponds surveyed, this study successfully quantified the dynamics of burrowing in these ponds and conclusions provide a useful basis for future studies and give suggestions of how other colonised fishponds may be affected.

Another migid in the wall: natural history of the endemic and rare spider Calathotarsus simoni (Mygalomorphae: Migidae) from a hill slope in central Argentina

A population of Calathotarsus simoni Schiapelli and Gerschman (1975) was discovered on a hillside in the Ventania system, Argentina. Our objectives were to quantify burrow density, record burrow morphology and door characteristics and describe the micro-habitat. We counted 57 burrows and report a density of 0.01 burrows/m2. Aggregation indices suggest that burrows are aggregated under some area plots but more evenly distributed on others. The trapdoor is thick and rigid with bevelled edges connected to the entrance rim by a narrow articulated hinge. Two egg sacs from females were obtained and data on eggs and spiderlings are presented. We registered six burrows of an undetermined species of Actinopus. While a few specimens of Actinopus sp. were found inhabiting this hillside, the highest proportion of burrows belonged to C. simoni. Spider diversity on the hillside shows the predominance of Linyphiidae, Nemesiidae and Gnaphosidae. One juvenile of C. simoni was captured using pitfall traps.

Camera Trapping: A Contemporary Approach to Monitoring Invasive Rodents in High Conservation Priority Ecosystems

Invasive rodent species have established on 80% of the world's islands causing significant damage to island environments. Insular ecosystems support proportionally more biodiversity than comparative mainland areas, highlighting them as critical for global biodiversity conservation. Few techniques currently exist to adequately detect, with high confidence, species that are trap-adverse such as the black rat, Rattus rattus, in high conservation priority areas where multiple non-target species persist. This study investigates the effectiveness of camera trapping for monitoring invasive rodents in high conservation areas, and the influence of habitat features and density of colonial-nesting seabirds on rodent relative activity levels to provide insights into their potential impacts. A total of 276 camera sites were established and left in situ for 8 days. Identified species were recorded in discrete 15 min intervals, referred to as ‘events’. In total, 19 804 events were recorded. From these, 31 species were identified comprising 25 native species and six introduced. Two introduced rodent species were detected: the black rat (90% of sites), and house mouse Mus musculus (56% of sites). Rodent activity of both black rats and house mice were positively associated with the structural density of habitats. Density of seabird burrows was not strongly associated with relative activity levels of rodents, yet rodents were still present in these areas. Camera trapping enabled a large number of rodents to be detected with confidence in site-specific absences and high resolution to quantify relative activity levels. This method enables detection of multiple species simultaneously with low impact (for both target and non-target individuals); an ideal strategy for monitoring trap-adverse invasive rodents in high conservation areas.

高原鼠兔有效洞穴密度对青藏高原高寒草甸群落植物生态位的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 高原鼠兔有效洞穴密度对青藏高原高寒草甸群落植物生态位的影响 DOI: 10.5846/stxb201305050926 作者: 作者单位: 兰州大学草地农业科技学院 草地农业生态系统国家重点实验室,兰州大学草地农业科技学院 草地农业生态系统国家重点实验室,兰州大学草地农业科技学院 草地农业生态系统国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（31172258）； 国家行业公益资助项目（201203041）； 国家科技支撑资助项目（2012BAD13B05） Effect of available burrow densities of plateau pika (Ochotona curzoniae) on plant niche of alpine meadow communities in the Qinghai-Tibet Plateau Author: Affiliation: State Key Laboratory of Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University,,State Key Laboratory of Grassland Agro-ecosystems, Lanzhou University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:高原鼠兔（Ochotona curzoniae）有效洞穴密度扩增会引起高寒草甸植物群落组分的变化。采用野外调查方法研究了高原鼠兔有效洞穴密度对青藏高原高寒草甸群落植物生态位的影响。结果表明：随高原鼠兔有效洞穴密度增加，样方内植物种数逐渐增多，但主要是毒杂草，有效洞穴密度超过15 个/625m2时豆科植物出现。优势种高山嵩草（Kobresia pygmaea）的重要值随有效洞穴密度增加呈单峰曲线，峰值出现在15 个/625m2。有效洞穴密度低于或等于21 个/625m2时，优势种高山嵩草生态位宽度位居第一，但有效洞穴密度达31 个/625m2时，其生态位宽度降至并列第三，低于小米草（Euphrasia pectinata）和钝裂银莲花（Anemone obtusiloba），等同于小花草玉梅（Anemone rivularis）和乳浆大戟（Euphorbia esula）。有效洞穴密度分别为10 个/625m2，15 个/625m2，21 个/625m2，31 个/625m2时，与高山嵩草生态位重叠度最大的物种分别为莓叶委陵菜（Potentilla fragarioides）、圆叶筋骨草（Ajuga ovalifolia）、乳浆大戟、条叶垂头菊（Cremanthodium lineare）。有效洞穴密度为10 个/625m2时，高山嵩草是群落内种群间竞争最激烈的一方，但有效洞穴密度超过或等于15 个/625m2时，高山嵩草则退出了种群间竞争最激烈的双方。说明高原鼠兔有效密度增加严重影响了高寒草甸群落组分、重要值、生态位宽度和生态位重叠值。 Abstract:The increase of available burrow density of plateau pika (Ochotona curzoniae) affects place or function of different plant in alpine meadow communities. A field survey was carried out to determine the effect of available burrow densities of plateau pika on plant niche characteristics of alpine meadow communities in the Qinghai-Tibet Plateau. This study showed that the number of present plant species increased and the more unpalatable plants were identified as the available burrow density of plateau pika increased. The legume plants were found as the available burrow density was over 15 per 625m2. With the increase of the available burrow density, the important value of Kobresia pygmaea, dominant plant, firstly increased and then decreased, peaking at 15 per 625m2 available burrow density. The niche breadth of K. pygmaea was the biggest among all plant populations of alpine meadow communities when the available burrow density was or below 21 per 625m2, but it became the tie for third and was lower than that of Euphrasia pectinata and Anemone obtusiloba, and equated to the niche breadth of A. rivularis and Euphorbia esula when the available burrow density was 31 per 625m2. The plants with the biggest niche overlap with K. pygmaea were P. fragarioides, Ajuga ovalifolia, E. esula, Cremanthodium lineare, at 10, 15, 21, 31 per 625m2 available burrow density respectively. The K. pygmaea was one of two populations which had the biggest coefficient of niche overlap at 10 per 625m2. However, K. pygmaea was not involved in the populations which had the biggest coefficient of niche overlaps when the available burrow density was or over 15 per 625m2.These results suggested that the increase of available burrow density of plateau pika changed the important value, niche breadth and niche overlap of different plant population in alpine meadow communities. 参考文献 相似文献 引证文献

高原鼠兔有效洞穴密度对高寒草甸优势植物叶片和土壤氮磷化学计量特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 高原鼠兔有效洞穴密度对高寒草甸优势植物叶片和土壤氮磷化学计量特征的影响 DOI: 10.5846/stxb201305070975 作者: 作者单位: 兰州大学,兰州大学,兰州大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31172258）；国家科技支撑项目（2012BAD13B05）；兰州大学中央高校基本科研业务费（lzujbky-2012-93） Effect of available burrow densities of plateau pika (Ochotona curzoniae) on leaf nitrogen and phosphorus stoichiometry of dominant plants and soil in alpine meadow Author: Affiliation: State Key Laboratory of Grassland Agro-ecosystems, Lanzhou University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用有效洞穴密度代替高原鼠兔（Ochotona curzoniae）活动强度的方法，研究了高原鼠兔有效洞穴密度（10、15、21和31 个/625 m2）对高寒草甸优势植物高山嵩草（Kobresia pygmaea）、垂穗披碱草（Elymus nutans）、小花草玉梅（Anemone rivularis）叶片和土壤氮（N）磷（P）化学计量特征的影响。结果表明，3种优势植物叶片N含量随有效洞穴密度增加而显著增加（P < 0.05），但叶片P含量却出现分异，表现为高山嵩草和垂穗披碱草叶片P含量随有效洞穴密度增加而先增加后降低（P < 0.05），小花草玉梅叶片P含量逐渐增加（P < 0.05）；高山嵩草叶片N：P随有效洞穴密度增加先降低后增加（P < 0.05），垂穗披碱草叶片N：P逐渐增加，小花草玉梅叶片N：P则先增加后降低。土壤0-10 cm和10-20 cm土层N含量随有效洞穴密度增加无明显变化；0-10 cm土层P含量随有效洞穴密度增加先降低后增加，10-20 cm土层P含量逐渐降低；0-10 cm土层N：P随有效洞穴密度增加无明显变化，而10-20 cm土层N：P则逐渐增加。优势植物叶片N、P、N：P与土壤N、P、N：P的相关性受植物根系分布特征和生存微环境的约束。 Abstract:A field survey was conducted to determine the effect of available burrow densities of plateau pika with 10, 15, 21 and 31 per 625 m2 on leaf nitrogen (N) and phosphorus (P) stoichiometry of dominant plants and soil of alpine meadow by using available burrow density substituting for activity degree of plateau pika in this study. The dominant plant included Kobresia pygmaea, Elymus nutans and Anemone rivularis var. flore-minore. This study showed that the leaf N content of K. pygmaea, E. nutans and A. Rivularis significantly increased as the available burrow density increased (P < 0.05). The leaf P content of K. pygmaea and E. Nutans firstly increased and then significantly decreased (P < 0.05), and leaf P of A. Rivularis increased gradually (P < 0.05) with the increase of available burrow density. The leaf N:P was different among three dominant plants, indicating that the leaf N:P of K. pygmaea significantly decreased (P < 0.05), and the leaf N:P of E. nutans increased gradually, but that of A. Rivularis firstly increased and then decreased as the available burrow density increased. This study also showed that the soil N content at 0-10 cm and at 10-20 cm layer was similar as the available burrow density increased. The soil P content at 0-10 cm layer firstly decreased and then increased, and that at 10-20 cm layer decreased with the increase of the available burrow density. The soil N:P at 0-10 cm layer was similar and that at 10-20 cm layer increased gradually in the increasing process of available burrow density. This study suggested that the correlation relationship between leaf N, P, N:P and soil N, P, N:P was regulated by distribution features of plant root systems and microhabitat where plants grow. 参考文献 相似文献 引证文献

Inclined heterolithic stratification in a mixed tidal–fluvial channel: Differentiating tidal versus fluvial controls on sedimentation

Tidal and fluvial processes control deposition and determine the sedimentological and ichnological character of sediments in the mixed tidal–fluvial Middle Arm, lower Fraser River, Canada. Sedimentological trends that define the mixed tidal–fluvial zone include: 1) mud beds present from the intertidal zone to the base of the channel, 2) a downstream increase in the number of mud beds, and 3) a lateral mud–sand–mud profile developed in the intertidal zone of each bar. Non-rhythmic deposition of sand under conditions of elevated river discharge is apparent, although sand beds are interbedded with cm- to dm-scale mud beds deposited during periods of low river discharge and increased tidal influence. In rare cases, mm- to cm-scale rhythmically alternating sand and mud lamina are deposited in successions of 12–14 beds (tidal rhythmites).Ichnologically, burrow density, trace size, and homogeneity in the vertical distribution of traces increase in the seaward direction. Burrows in all of the bars are evenly distributed in the vertical profile through substrates of similar grain size; however, infaunal distributions vary as a function of grain size and subaerial exposure. Muddier sediments and substrates that experience less subaerial exposure display a higher degree of bioturbation (bioturbation index [BI] 2–5). Sand beds are generally bioturbated to a lesser degree (BI 0–1) except in the lower delta plain, where higher degrees of bioturbation (BI 3–5) can be produced.The sedimentological and ichnological character of sediments in the tidal–fluvial Middle Arm showcases subtle, but important differences between tide-influenced, river-dominated inclined heterolithic stratification (IHS) and mixed tidal–fluvial IHS. In particular, more homogeneous and diverse burrowing in both mud and sand beds, more rhythmic sand–mud interbedding, mud deposition to the base of the channel, and the development of a mud–sand–mud profile along the length of the bar are considered indicative of heightened tidal influence and sustained brackish-water conditions.

Impact of Off-road Vehicles (ORVs) on Ghost Crabs of Sandy Beaches with Traffic Restrictions: A Case Study of Sodwana Bay, South Africa

Off-road vehicles (ORVs) are popular in coastal recreation, although they have negative impacts on sandy shores. In South Africa, ORVs are banned from most coastal areas, while some areas are designated for restricted ORV use, providing an opportunity to assess whether ORV traffic restrictions translate into biological returns. In Sodwana Bay, the impact of ORVs on ghost crab populations was investigated. During Easter 2012, ghost crab burrows were counted on beach sections open and closed to traffic. Burrow density in the Impact section was less than a third that of the Reference section, and by the end of the study burrow size in the Impact section was half that of the Reference section. ORV traffic caused a shift in burrow distribution to the Lower beach. However, differences in burrow densities between sections were 14 times smaller than differences obtained at a time when ORV use in Sodwana Bay was not controlled. While confirming the well-established detrimental effects of ORV use on sandy beach ecosystems, results demonstrated that traffic restrictions on beaches measurably minimize impacts to the fauna, thus translating into clear-cut biological returns.

The influence of soil type, congeneric cues, and floodplain connectivity on the local distribution of the devil crayfish (Cambarus diogenes Girard)

AbstractBurrowing crayfish are potentially important ecological links between terrestrial and aquatic systems, but little is known about what drives their local distribution patterns. We investigated potential mechanisms underlying the patchy local distribution of the devil crayfish (Cambarus diogenes Girard) in a stream floodplain ecosystem of the coastal plain of Alabama. We used a series of field surveys and laboratory trials to: 1) quantify local distributions and soil-type associations, 2) identify soil preferences of juveniles and adults, 3) examine the effects of biotic (adult occupancy) and abiotic (soil compaction) factors on juvenile burrowing preferences, and 4) investigate the role of floodplain connectivity on burrow density. Juvenile crayfish were more abundant in sandy streamside soils, whereas adults were more abundant in clay-based floodplain soils. In laboratory preference trials in artificial burrowing chambers, adults and juveniles showed affinity for floodplain over streamside soils, ...

Establishing accurate baseline estimates of breeding populations of a burrowing seabird, the grey-faced petrel (Pterodroma macroptera gouldi) in New Zealand

Accurate estimates of breeding population size are essential for detecting change and guiding conservation management and sustainable use. In New Zealand, the grey-faced petrel (Pterodroma macroptera gouldi) now breeds predominantly on offshore islands, but is also subject to customary harvest of chicks by northern tribes of Māori (New Zealand’s indigenous peoples). We used island-wide surveys of 3186 breeding burrows, corrected for detection error, and associated habitat variables on two island systems (Ruamaahua Islands and Moutohorā), combined with data from geographic information systems, to build hierarchical Bayesian models to predict the distribution and abundance of breeding pairs. Burrow densities increased with elevation on all islands and, on Moutohorā, were lesser in gullies and on terraces. On the Ruamaahua Islands, burrow densities were associated positively with deeper soils and forests dominated by pōhutukawa (Metrosideros excelsa), and negatively with taller forest, denser canopy cover, and northern and western aspects. Predicted breeding-pair densities for each island group provided breeding-pair population estimates of 72,410 (95% credible interval 14,280–138,400) across the Ruamaahua Islands and 69,330 (10,590–128,300) on Moutohorā. Estimating burrow densities using habitat characteristics provided greater precision and accuracy than simpler models that extrapolate sampling data over larger areas. The methods used to estimate population size are applicable to other cryptic seabird species, especially those that live or breed in burrows. It is important to establish accurate baseline estimates of the populations of common seabird species against which to determine responses to perturbations and management interventions.

Tree ring growth and stable isotopes as potential indicators of historical seabird activities on forested islands in coastal British Columbia

We examined yearly rings from increment cores of conifers on two seabird nesting islands (one in the Lucy Islands and one in the Rankine Islands, British Columbia), to determine whether trees contained signatures of historical activity of seabirds. Ten conifers (primarily Sitka Spruce, Picea sitchensis), ranging from 56 cm to 127 cm diameter (average 90 cm) and ranging from 70 to 232 years in age (average 132 years of age), were cored across a 200-m gradient in densities of seabird burrows. At the site in the lucy Islands, annual growth was highest (8–14 mm) in the trees with the highest seabird burrow densities and highest in the earliest rings (~1930), which were followed by a fluctuating reduction down to ~2 mm/year in the year 2000, but with a secondary elevated growth period in the 1970s. Adjacent control trees without seabird burrows had a growth rate of ~2 mm/year throughout the same period. At the site in the Rankine Islands, growth rates were also variable and exhibited a 10–15 year non-synchronous periodicity, with the highest growths in the location with high seabird burrow density. Nitrogen isotope signatures (δ15N), which are greatly elevated in seabird guano, ranged from minus 3.9% to 17.4% among tree rings (n = 245 rings) and were positively correlated to percentage nitrogen in rings, average ring growth, and burrow densities. Using these methods, we infer from our tree ring data that seabird activity declined on the lucy Islands over a 70-year period and that the combination of growth, nitrogen isotopic signatures, and percentage nitrogen in tree rings as well a more detailed sampling grid of target and adjacent control trees will provide seabird biologists with additional tools for evaluating spatial and historical trends in seabird activity on forested islands.

Degradation of wetlands on the Qinghai-Tibet Plateau: A comparison of the effectiveness of three indicators

Abstract The Qinghai-Tibet Plateau encompasses a large quantity of wetlands, some of which have been degraded to varying severity levels. In the literature, a number of degradation indicators have been proposed to evaluate ecological health of wetlands, but their effectiveness in the plateau environment remains unknown. In this study, we assessed the effectiveness of three degradation indicators, soil moisture content at 10 cm deep, vegetative cover, and density of pika burrows. The degradation severity of wetlands in Maduo County on the Qinghai-Tibet Plateau is enumerated at four levels, intact, slight, moderate and severe. Analysis of 106 samples collected in the field demonstrates that the density of pika burrows is the least reliable indicator. By comparison, vegetative cover and underlying soil moisture content are more reliable, even though neither is a perfect indicator as the difference among adjacent levels of severity as revealed by t-test is not always statistically significant. The imperfection of vegetative cover as an indicator is due to its variation among different types of wetlands. The limitation of moisture content is attributed to its non-linear relationship with wetland degradation. Above the threshold of about 50% in moisture content wetlands are unlikely to be degraded. It is recommended that moisture be measured at the point near the surface and vegetative cover be further differentiated by species in order to improve their effectiveness.

Incidence of plastic fragments among burrow-nesting seabird colonies on offshore islands in northern New Zealand

Marine plastic pollution is ubiquitous throughout the world’s oceans, and has been found in high concentrations in oceanic gyres of both the northern and southern hemispheres. The number of studies demonstrating plastic debris at seabird colonies and plastic ingestion by adult seabirds has increased over the past few decades. Despite the recent discovery of a large aggregation of plastic debris in the South Pacific subtropical gyre, the incidence of plastics at seabird colonies in New Zealand is unknown. Between 2011 and 2012 we surveyed six offshore islands on the northeast coast of New Zealand’s North Island for burrow-nesting seabird colonies and the presence of plastic fragments. We found non-research related plastic fragments (0.031pieces/m2) on one island only, Ohinau, within dense flesh-footed shearwater (Puffinus carneipes) colonies. On Ohinau, we found a linear relationship between burrow density and plastic density, with 3.5 times more breeding burrows in areas with plastic fragments found. From these data we conclude that plastic ingestion is a potentially a serious issue for flesh-footed shearwaters in New Zealand. Although these results do not rule out plastic ingestion by other species, they suggest the need for further research on the relationship between New Zealand’s pelagic seabirds and marine plastic pollution.

Spatial Ecology of Fiddler Crabs,Uca pugnax, in Southern New England Salt Marsh Landscapes: Potential Habitat Expansion in Relation to Salt Marsh Change

The spatial distribution of the fiddler crab Uca pugnax (Atlantic Marsh Fiddler Crab) in relation to salt marsh patch structure was investigated along the central Connecticut coast of Long Island Sound. Salt marsh landscape structure at the study sites exhibit characteristics consistent with changes noted in other systems along the US Atlantic coast over the last several decades, including significant seaward erosion, encroachment of low-marsh plants into high marsh, changing composition of high-marsh plant patch structure, and marsh dieback and drowning. Our objective was to determine whether the spatial patterns of U. pugnax inhabiting these systems differed from those previously reported for southern New England in light of these characteristics. Densities of crab burrows were highest in low-marsh patches of Spartina alterniflora (Atlantic Smooth Cordgrass) and unvegetated muds along tidal creek banks and mosquito ditches. Seaward-eroding low-marsh areas were generally devoid of live crabs and burrows. Crab-burrow densities varied across the complex patch mosaics in high-marsh areas. Burrow densities were generally low in the extensive short S. alterniflora patches that comprised much of the high-marsh area at several sites. However, high burrow densities, equivalent to low-marsh densities, were found in certain high-marsh patch types and upland transition zones. These included patches of Spartina patens (Marsh Hay Cordgrass), Distichils Spicata (Desert Salt Grass), and mixes of these, and particularly in S. patens patches wholly or partly comprised of hummocks of vegetation surrounded by bare sediment. At several sites, burrow densities were high in upland transition zone patches of Phragmites australis (Common Reed). As such, crab-burrow distributions were highly variable at local, within-marsh system spatial scales. Live U. pugnax were found regularly in all patch types on all marshes. Our results indicate a much broader distribution of U. pugnax at relatively high densities across southern New England marsh landscapes than previously reported. This finding may represent a case of habitat expansion in response to salt marsh change, likely due to sea-level rise and other factors, creating high-marsh habitats in a variety of patch types that can support resident populations of fiddler crabs. Such an expansion of a dominant salt marsh species, which can significantly affect ecosystem dynamics, may potentially increase the complexity of current salt marsh change patterns and dynamics along southern New England coastlines.

Metapopulation Dynamics of a Burrowing Herbivore Drive Spatio-temporal Dynamics of Riparian Plant Communities

Animals can modify their environment by consumptive and physical activities such as herbivory and soil disturbance. Engineering species may create structures that long outlive them and have lasting impacts on local communities of plants and animals. Water voles, Arvicola amphibious, are rodents that visibly impact riparian plant communities by grazing on surface and root vegetation and excavating long-lasting burrow systems. This species has a metapopulation structure and occurs across patches which are subject to frequent extinction and colonization events, causing spatially heterogeneous disturbances across the landscape. Using a chronosequence of water vole occupancy in the Highlands of Scotland, we show that heterogeneity in plant community composition and structure—both within and between colony patches—was related to cumulative measures of past physical impact: burrow density and time since a patch was last occupied by voles, rather than to current indices of vole occupancy. In our sample of 107 patches monitored over 5 years, no fewer than 31 unique patch occupancy histories were found, each with potentially subtle differences in the accumulated influence of water vole herbivory and engineering. As a result, a patchwork of different plant successional stages occurs across the riparian landscape which is both created and maintained by water vole extinction-colonization dynamics. We propose that the water vole-vegetation system can be described as a metacommunity where dispersal by a higher tropic agent at the landscape scale influences the spatial dynamics of plants at the patch level.

A Model Approach for Estimating Colony Size, Trends, and Habitat Associations of Burrow-Nesting Seabirds

Abstract. We present a prototype monitoring strategy for estimating the density and number of occupied burrows of burrow-nesting seabirds. We use data and management questions from Washington State as an example that can be applied to burrow-nesting seabirds at single- or multi-island scales. We also demonstrate how habitat assessments can be conducted concurrently. Specifically, we compared the density and occupancy of burrows of the Rhinoceros Auklet (Cerorhinca monocerata) at nesting colonies in the California Current and the Salish Sea and in the 1970s, 1980s, and today. We estimated 36 152, 1546, and 6494 occupied burrows on Protection and Smith islands (Salish Sea), and Destruction Island (California Current), respectively. Our estimates for the Salish Sea are 52% greater than those from the 1970s and 1980s, while that for the California Current is 60% less than that of 1975. This suggests that the Salish Sea population has increased, despite greater human effects on that ecosystem. However, some of...

Relationship between habitat characteristics and densities of southern Idaho ground squirrels

Many wildlife species living in sagebrush-steppe habitats of the Intermountain West of the United States have experienced population declines. Effective management of such species, especially restoration efforts, is contingent on understanding relationships between habitat characteristics and population densities of the target species. Unfortunately, even such basic information is often lacking. The goal of this 2-year study was to determine the relationship between southern Idaho ground squirrel (Urocitellus endemicus) population densities and habitat variables: soils (texture), topography (slope, aspect), and vegetation (canopy cover, species diversity). We measured population density indirectly through burrow entrance counts and categorized them into high-burrow and low-burrow densities. We used logistic regression and Akaike's Information Criterion to identify a best subset of models. We employed model averaging and calculated odds ratios for averaged parameter estimates found in the best models. A high density of burrows was associated with greater percentages of silt; east-facing aspects; greater plant species diversity; and greater cover of perennial grasses, perennial grasses and forbs, and native perennial forbs. Low burrow density was associated with greater percentages of sand; south-facing aspects; greater cover of exotic annuals; and lesser plant species diversity. Management of southern Idaho ground squirrel habitat should focus on protecting areas with existing native vegetation and restoring native, perennial vegetation in areas that are infested with exotic annuals, especially in areas possessing suitable soil types and topographic features. © 2013 The Wildlife Society.