Altered Habitat Conditions Research Articles

Salinity Effects on Phragmites Decomposition Dynamics Among the Hudson River’s Freshwater Tidal Wetlands

Sea level rise due to climate change will expose Hudson River tidal marshes to chronic shifts in salinity, thus altering habitat conditions and biogeochemical processes. Increased salt intrusion may affect macroinvertebrate and microbial communities that are important in the decomposition of a dominant, invasive plant species Phragmites australis. We hypothesized that increased salinity intrusion will negatively affect macroinvertebrate and microbial litter breakdown processes. Field and laboratory experiments were conducted to test the effect of salinity on Phragmites decomposition. Leaf packets were incubated among tidal wetlands along a salinity gradient and used to compare microbial respiration, fungal biomass, and mass loss. In addition, salinity tolerance of a freshwater isopod (Caecidotea sp.) and heterotrophic microbes were examined using laboratory bioassays. Salinity negatively affected isopod survivorship and microbial activity in controlled laboratory experiments; however, salinity did not significantly account for in situ variation in Phragmites mass loss, microbial respiration, and fungal biomass among wetlands. Future studies need to include litter from additional wetland species and consider alternative controls on decomposition (e.g., variation in temperature or inorganic nutrients) in order to best forecast the long-term impact of sea-level rise and salinity increases among tidal freshwater wetlands.

Empirical and simulation evaluations of an abundance estimator using unmarked individuals of cryptic forest-dwelling taxa

Conservation and management programs use populations of sentinel taxa, such as stream-associated amphibians, as indicator species due to their perceived sensitivity to environmental change. Estimating population size with traditional tools such as mark–recapture estimators may be impractical for forest-dwelling stream-associated amphibians, many of which are cryptic and have low detection probabilities. In addition, sampling techniques can alter habitat conditions, particularly with repeat sampling, and compromise inferences about management impacts. We used simulated and empirical data and N-mixture models to estimate detection probabilities and abundances for two amphibian genera, giant Dicamptodon and torrent Rhyacotriton salamanders, sampled with a less-invasive approach than other methods. We surveyed forested headwater streams located in western Washington, USA, for salamanders 7 July–27 August 2008. We assessed model sensitivity to changes in animal abundance (5 and 15) and detection probability (0.05–0.5), as well as study design alternatives including number of sample plots (50–150) and number of sampling visits (2–4). We also evaluated the effects of stream temperature and stream order on detection probability using data collected from forested streams in Washington, USA. Precision of detection probability estimates improved as the number of plots and sampling occasions increased. Variability of estimated population sizes decreased with higher detection probability, although species abundance had little effect on precision of detection probability estimates. Detection probability estimated from empirical data ranged from 0.07 to 0.65 for giant salamanders and 0.06–0.67 for torrent salamanders. Giant salamander detection probability was positively associated with stream temperature regardless of stream order, and was higher in second- and third-order streams than first-order streams. Detection probability for torrent salamanders varied with stream temperature, order, and the interaction of those covariates, with detection increasing with temperature for second- and third-order streams but showing a flat or decreasing trend for first-order streams. N-mixture models, paired with careful consideration of study design alternatives, can produce robust estimates of abundance and obviate the traditional reliance on indices of relative abundance for many rare and sensitive taxa. Use of a less invasive technique for sampling stream-associated amphibians resulted in sufficient animal captures for suitable model performance. Our simulation results can inform study design and direct efficient allocation of field effort.

A comparison of avian communities and habitat characteristics in floodplain forests associated with valley plugs and unchannelized streams

AbstractChannelization of streams associated with floodplain forested wetlands has occurred extensively throughout the world and specifically in the southeastern United States. Channelization of fluvial systems alters the hydrologic and sedimentation processes that sustain these systems. In western Tennessee, channelization and past land‐use practices have caused drastic geomorphic and hydrologic changes, resulting in altered habitat conditions that may affect avian communities. The objective of this study was to determine if there were differences in avian communities utilizing floodplain forests along unchannelized streams compared to channelized streams with valley plugs, areas where sediment has completely filled the channel. During point count surveys, 58 bird species were observed at unchannelized sites and 60 species were observed at valley plug sites. Species associated with baldcypress‐tupelo (Taxodium‐Nyssa) swamps (e.g. Great Egret (Ardea albus) and Black‐crowned Night Heron (Nycticorax nycticorax)) and mature hardwood forests with open midstories (e.g. Eastern Wood‐Pewee (Contopus virens), Yellow‐throated Vireo (Vireo flavifrons), Cerulean Warbler (Dendroica cerulea) and Scarlet Tanager (Piranga olivacea)) were either only found at unchannelized sites or were more abundant at unchannelized sites. Conversely, species associated with open and early successional habitats (e.g. Tree Swallow (Tachycineta bicolor), Northern Mockingbird (Mimus polyglottos) and Blue Grosbeak (Passerina caerulea)) were either only found at valley plug sites or were more abundant at valley plug sites. Results of habitat modelling suggest that the habitat characteristics of floodplain forests at unchannelized sites are more suitable for Neotropical migrant bird species of conservation concern in the region than at valley plug sites. This study, in combination with previous research, demonstrates the ecological impacts of valley plugs span across abiotic and biotic processes and tropic levels. Copyright © 2010 John Wiley & Sons, Ltd.

Partitioning the effects of an ecosystem engineer: kangaroo rats control community structure via multiple pathways

1. Ecosystem engineers impact communities by altering habitat conditions, but they can also have strong effects through consumptive, competitive and other non-engineering pathways. 2. Engineering effects can lead to fundamentally different community dynamics than non-engineering effects, but the relative strengths of these interactions are seldom quantified. 3. We combined structural equation modelling and exclosure experiments to partition the effects of a keystone engineer, the giant kangaroo rat (Dipodomys ingens), on plants, invertebrates and vertebrates in a semi-arid California grassland. 4. We separated the effects of burrow creation from kangaroo rat density and found that kangaroo rats increased the diversity and abundance of other species via both engineering and non-engineering pathways. 5. Engineering was the primary factor structuring plant and small mammal communities, whereas non-engineering effects structured invertebrate communities and increased lizard abundance. 6. These results highlight the importance of the non-engineering effects of ecosystem engineers and shed new light on the multiple pathways by which strong-interactors shape communities.

Conservation and management of ecological systems in a changing California

Climate change in California is altering habitat conditions for many species and exacerbating stress from other factors such as alien invasive species, pollution, and habitat fragmentation. However, the current legal and planning framework for species protection does not explicitly take climate change into account. The regulatory framework is primarily reactive, kicking in only after species' health is gravely threatened. Neither federal nor state regulations require forward-looking, climate-sensitive species or ecosystem protection plans. Habitat planning is poorly funded and often piecemeal. In this context, the wrong lands may be protected, with development allowed to occur in areas that would be most beneficial for species conservation in the future. A more forward-looking approach to habitat conservation is needed, one based on a statewide strategy to identify and protect critical habitat areas, including corridors to enable species migration. The approach would also require development of assessment indicators and assistance strategies not dependent on current habitat structure, and a governance structure to implement regular, periodic updates of management plans in relation to agreed-upon performance indicators. Such a strategy should integrate habitat conservation planning with other state and regional plans and objectives, such as for transportation infrastructure, urban development, and mitigation of climate change.

Insect Responses to Major Landscape-Level Disturbance

Disturbances are abrupt events that dramatically alter habitat conditions and resource distribution for populations and communities. Terrestrial landscapes are subject to various disturbance events that create a matrix of patches with different histories of disturbance and recovery. Species tolerances to extreme conditions during disturbance or to altered habitat or resource conditions following disturbances determine responses to disturbance. Intolerant populations may become locally extinct, whereas other species respond positively to the creation of new habitat or resource conditions. Local extinction represents a challenge for conservation biologists. On the other hand, outbreaks of herbivorous species often are triggered by abundant or stressed hosts and relaxation of predation following disturbances. These insect responses can cause further changes in ecosystem conditions and predispose communities to future disturbances. Improved understanding of insect responses to disturbance will improve prediction of population and community dynamics, as well as ecosystem and global changes.

Domesticated ecosystems and novel communities: challenges for the management of large rivers

Throughout the last centuries most large rivers have increasingly become humandominated ecosystems as a result of land reclamation, floodplain drainage, hydropower production, and channelization for navigation. Their domestication, i.e. their optimization for few ecosystem services, has fundamentally altered habitat conditions and led to the formation of novel biotic communities as well as to the truncation of vital ecosystem processes. Current conservation and management strategies do not yet cope with the dramatic alterations of large rivers. Concurrently, river management competes with the more human-focused targets and directives in the energy, flood control and agricultural sectors. Therefore, there is an urgent need for innovative, adaptive strategies to sustainably manage domesticated large rivers through increasing levels of active intervention.

Reduced risk for positive soil-feedback on seedling regeneration by invasive trees on a very nutrient-poor soil in Seychelles

Invasive plants sometimes alter habitat conditions so as to promote further invasion, either by the same or by other non-native species. Such positive feedbacks often occur because the non-native species increases soil fertility, thereby favouring recruitment of non-native seedlings. This has been demonstrated in nitrogen-poor habitats invaded by nitrogen-fixing species, but it is unclear whether similar processes operate in habitats limited by phosphorus and other nutrients. I compared the growth of seedlings of Cinnamomum verum, an abundant invasive tree on phosphorus-poor soils in the Seychelles, in soils taken from beneath different tree species. I expected that soil phosphorus availability would be higher beneath stands of C. verum than beneath stands of either the native Northea hornei or the non-native nitrogen-fixing species, Falcataria moluccana. I therefore predicted that C. verum seedlings would grow faster in soil taken from beneath C. verum trees than in soil taken from beneath either of the other two species. To test this hypothesis, I performed a bioassay experiment with seedlings of C. verum grown in soils from stands of C. verum, F. moluccana and N. hornei. Different nutrient treatments (control, plus phosphorus (P), plus nitrogen (N), plus N and P, and plus complete fertilizer) were applied to investigate how nutrient availabilities modulate the effects of the trees. In the control treatment without added nutrients, there was a weak tendency for seedlings to perform better in the soils from beneath invasive than native trees. However, seedling growth in soils from beneath invasive species was markedly higher following the addition of phosphorus in the case of the F. moluccana soil, and complete fertilizer in the case of the C. verum soil. These results indicate that on very nutrient-poor soils, a low supply of nutrients other than N may reduce the risk of a soil-feedback by invasive trees on seedling regeneration.

Implications of climate warming for Boreal Shield lakes: a review and synthesis

Climate change is a reality. A warming climate will have large effects on lakes of the Boreal Shield. Our ability to forecast these effects, however, is hampered by a very incomplete understanding of the actual interactions between weather and many aspects of lake ecosystems. Climate change will affect lakes in very complex ways. Changing weather conditions will have direct effects on thermal habitats; however, there will also be very important indirect effects on lake ecosystems through influences on watershed processes that affect the thermal and chemical characteristics of lakes. Altered habitat conditions will affect the resident biota in both positive and negative ways and may favour range expansions of some native and non-native species. Our understanding of the altered biological interactions that will structure lake communities in a warmer climate is still limited, making the prediction of biological outcomes very difficult. Modelling efforts, experiments and empirical analyses of relationships between important attributes of lakes, lake communities, and weather conditions in the past are beginning to further our ability to predict likely future effects. Much more work is needed in all these research areas to further our understanding of the probable effects of climate change on Boreal Shield lakes. Because of the potential interactions of climate with other large-scale environmental stressors such as UV-B irradiance, exotic species invasions, base cation depletion, and acidification, future studies need to consider multiple stressor effects.

Changes in the species composition and distribution of butterflies (Rhopalocera) in Cracow (Poland) since the mid-19th century

Qualitative changes in the diurnal lepidopteran fauna of the Cracow area have been studied over a period beginning in the mid-19 th century. Sources of data included the scientific collections of the Institute of Systematics and Evolution of Animals, PAS, some private collections and data from the authors' own studies (2000-2003). In the historical period covered by the study (three time intervals), a total of 99 species of Rhopalocera were recorded. Altogether, negative population trends were recorded in 46 species, including 27 species that withdrew from the study area; positive trends were demonstrated in 33 (including 20 new arrivals), and 20 species were shown to have more or less stable populations. The most powerful adverse impact was that exerted by natural factors (which affected 28 species), much less that due to a combination of natural and anthropogenic factors (in 8 species) or to anthropogenic factors alone (10 species). Some species of Rhopalocera manifested considerable adaptability to altered habitat conditions. Among the recorded species, 11 are under strict legal protection in Poland. The long term survival chances of endangered species could be enhanced by active protection of the habitats, with natural reserves as the most important measure.

Relationships between vegetation patterns and periglacial landforms in northwestern Svalbard

We studied the small-scale vegetation pattern in the high Arctic at Ny Alesund to assess if the plant distribution was related to periglacial landforms. The whole area has been deglaciated for millennia but only a modest part of the area was covered by mature vegetation. The plant cover varied considerably in relation to ground patterning originated by periglacial processes, especially frost heave, frost creep, gelifluction and ice segregation, giving rise to a mosaic of microhabitats sharply differing from each other as regards physical properties and microclimate. The distributional patterns of vascular plants, lichens and bryophytes were primarily affected by complex responses to substrate texture, soil moisture content and substrate disturbance. Since global warming will probably affect both periglacial processes and plant responses to altered habitat conditions, we concluded that long-term monitoring of relationships between landforms and vegetation represents a suitable tool for assessing the impact of global change on arctic regions.

Typology and Type Specific Reference Conditions for Medium-Sized and Large Rivers in North Rhine-Westphalia: Methodical and Biological Aspects

According to the ‘EU Water Framework Directive’ the assessment of the ecological quality of streams and rivers should be based on type specific reference conditions. In Central Europe, stream sections suited to serve as reference sites for the high ecological status of rivers are rarely found, due to long lasting anthropogenic impact on virtually all rivers. We present a method for the description of reference conditions for medium-sized and large rivers, which has been developed and tested for rivers in North Rhine-Westphalia (Germany). Present data on the fauna proved to be sufficient for the description of river types, at least on a rough scale. However, even the fauna of the least deteriorated Central European river sections is very different to the ‘historical’ fauna. Therefore, the biological reference conditions are only partially based on investigations in the present fauna. It is indispensable to use additional sources to describe ‘reference communities’, particularly historical literature data. Furthermore, considerations on only slightly altered habitat-conditions in rivers and on landscape patterns under pristine conditions are taken into account.

Long‐term effects of frequent low‐intensity burning on ant communities in coastal blackbutt forests of southeastern Australia

AbstractPeriodic low‐intensity fire (hazard‐reduction burning) is a conspicuous management strategy in virtually all of Australia’s dry forest communities where it is primarily used to reduce fuel levels with the intention of minimising the extent and severity of wildfires. Little is known, however, about the effects of its repeated use on natural ecosystems over long periods of time. This study investigated the long‐term effects of frequent low‐intensity fire on forest ant communities by comparing frequently burnt sites with long‐unburnt control sites. While the richness of ant communities remained largely unchanged, the composition of assemblages differed substantially between treatments. Although frequent burning apparently resulted in the loss of a substantial number of species, the overall richness of frequently burnt areas was maintained by the addition of species not present on unburnt sites. These changes in species composition were accompanied by major changes in community organisation (structure) and were considered to be a response to altered habitat conditions, particularly litter biomass, vegetation structure and patterns of insolation at ground level. Appropriate fire prescriptions could therefore be applied to manipulate these habitat elements at a landscape scale to meet both management and conservation goals. A comparison of pitfall trapping and litter extraction techniques revealed the importance of a composite sampling strategy, with 22% of ant species detected only by litter extraction.

Characterization of Sympatric or Adjacent Habitats of 2 Deer Species in West Texas

Fourteen vegetative parameters and a Land Surface Ruggedness Index (LSRI) were quantified on 306,000 ha of rangeland in western Texas and eastern New Mexico that differentially supported high and low densities of desert mule deer (Odocoileus hemionus crooki) and white-tailed deer (0. virginianus texanus). Percent woody cover was the only parameter measured that was significantly different (P 75%. Increases in white-tailed deer densities were positively correlated (r = 0.69, P < 0.001) with increases in percent woody cover. Using the measurement of percent woody cover, we correctly classified 83 and 65% of the 17 study areas into high and low density classes, respectively, for white-tailed deer and desert mule deer. It is apparent that desert mule deer populations on rangelands in this region could be enhanced by limiting woody plant canopy cover in their habitats to about 40%. Conversely, white-tailed deer populations would be favored by encouraging brush encroachment above this level. J. WILDL. MANAGE. 50(1):129-134 The Trans-Pecos and Panhandle regions of west Texas accommodate ranges of both desert mule deer and white-tailed deer. Landowners, spo smen, and biologists are concerned about an apparent population decline in desert mule deer and an increase in white-tailed deer in areas traditionally considered desert mule deer range (Harwell and Gore 1981). Although no substantive data are available, it is thought that this situation resulted from brush infestation 'Present address: School of Forestry, Fisheries, and Wildlife, 112 Stephens Hall, University of MissouriColumbia, Columbia, MO 65211. 2 Present address: Caesar Kleberg Wildlife Research Institute, P.O. Box 218, Texas A&I University, Kingsville, TX 78363. This content downloaded from 157.55.39.236 on Tue, 11 Jul 2017 17:51:06 UTC All use subject to http://about.jstor.org/terms 130 DEER IN WEST TEXAS * Wiggers and Beasom J. Wildl. Manage. 50(1):1986 (Humphrey 1958, Johnston 1963, U.S. Dep. Agric. 1964) that has altered habitat conditions to favor white-tailed deer (Harwell and Gore 1981). Krfimer (1972) reported similar patterns of white-tailed deer encroachment in the westcentral United States and southern Canada. He suggested that the increasing densities of woody vegetation along water channels may have influenced a shift in species ratio favoring whitetailed deer. Habitat requirements for either deer species in west Texas are not well defined, especially on sympatric and adjacent ranges. This knowledge is essential before concerns regarding the future status of the desert mule deer can be addressed. Further, the lack of habitat information restricts the formulation of management guidelines for possible habitat improvement for either species. Our objective was to determine if selected habitat attributes differentially influenced population levels of desert mule deer and white-tailed deer. Support for this work was provided by the U.S. For. Serv., Rocky Mt. For. and Range Exp. Stn., and the Dep. Range and Wildl. Manage., Texas Tech Univ. We thank the many private ranchers in west Texas and personnel of the Tex. Parks and Wildl. Dep., the U.S. Soil Conserv. Serv., the U.S. Natl. Park Serv., and the U.S. Bur. Land Manage. (BLM) for their support in this project. STUDY AREAS AND METHODS Study areas were selected that were known to support or previously have supported populations of both deer species. They included all or parts of 30 private ranches, 1 state and 1 federally administered park in west Texas, and the Mescalero Sands area in southeastern New Mexico (Fig. 1). These areas totaled 306,000 ha of habitat where desert mule deer and whitetailed deer populations are sympatric or contiguously allopatric. Overlapping populations of desert mule deer and white-tailed deer in Texas occur in the Panhandle and Trans-Pecos geographic regions (Harwell and Gore 1981, Russ 1981). In the Panhandle Region, including the Mescalero Sands in southeastern New Mexico, deer are associated primarily with the Rolling Plains Physiographic Area. The Rolling Plains occupies a zone between the arid, desert regions to the southwest and the more humid regions to the east. Precipitation averages about 52 cm NEW MEXICO