Summer Habitat Research Articles

Gulf Sturgeon Movements in the Pearl River Drainage and the Mississippi Sound

AbstractA study of the seasonal movements of Gulf sturgeon Acipenser oxyrinchus desotoi was conducted in the Pearl River system and the Mississippi Sound from 2000 through 2003. We captured or recaptured, marked, and released 503 Gulf sturgeon, 98 adults being tagged with internal or external telemetry tags. Movement chronologies were generally similar to those reported in other studies. Summer habitats were found in the Pearl and Bogue Chitto rivers (Louisiana–Mississippi), and these habitats were occupied from April through November. Adults and subadults were spatially separated, the adults being concentrated in the Bogue Chitto River and the subadults in the Pearl River. Tagged adults began to leave the summer habitat during September and to arrive at the mouth of the Pearl River and the Rigolets Pass. The last departure from this location was in late November. Wintering habitat between Cat, Ship, Horn, and Petit Bois islands in the Mississippi Sound was used between November and early March. Gulf sturgeon returned to the Rigolets Pass from March through June. Despite extensive sampling and the use of multiple collection gears, no eggs, larvae, or age‐0 fish were captured and Gulf sturgeon spawning sites within this system remain unknown. The identification of summer and wintering habitats is essential for critical habitat designation for this species, which is federally listed as threatened.

Effects of hypoxia on scope-for-activity and power capacity of lake trout (Salvelinus namaycush)

This study develops a quantitative model of the combined effects of temperature and ambient dissolved oxygen on metabolic scope-for-activity and power capacity of juvenile lake trout (Salvelinus namaycush). The model provides a framework for evaluating the effects of hypoxia on the capacity of lake trout to perform critical daily life support activities. Maximum power output for sustained swimming of yearling lake trout occurred at 12–20 °C and a dissolved oxygen concentration of >7 mg·L–1. At 4–8 °C, temperatures typical of the hypolimnetic summer habitat of juvenile lake trout, maximum power capacity was reduced by 33%, 67%, and 100% at ambient dissolved oxygen concentrations of 7, 5, and 3 mg·L–1, respectively. Analysis of power outputs, growth impairment, and recruitment success indicated that attainment of 3/4 power capacity would accommodate most daily life support activities of juvenile lake trout. At 4–14 °C, the threshold dissolved oxygen concentration for attainment of 3/4 scope-for-activity varied from 7.5 to 6.6 mg·L–1, respectively, with a mean and standard deviation of 7.04 ± 0.33 mg·L–1. A dissolved oxygen criterion of 7 mg·L–1is recommended for protection of the hypolimnetic habitat of juvenile lake trout.

Predicting Minimum Habitat Characteristics for the Indiana Bat in the Champlain Valley

Predicting potential habitat across a landscape for rare species is extremely challenging. However, partitioned Mahalanobis D2 methods avoid pitfalls commonly encountered when surveying rare species by using data collected only at known species locations. Minimum habitat requirements are then determined by examining a principal components analysis to find consistent habitat characteristics across known locations. We used partitioned D2 methods to examine minimum habitat requirements of Indiana bats (Myotis sodalis) in the Champlain Valley of Vermont and New York, USA, across 7 spatial scales and map potential habitat for the species throughout the same area. We radiotracked 24 female Indiana bats to their roost trees and across their nighttime foraging areas to collect habitat characteristics at 7 spatial scales: 1) roost trees, 2) 0.1-ha circular plots surrounding the roost trees, 3) home ranges, and 4–7) 0.5-km, 1-km, 2-km, and 3-km buffers surrounding the roost tree. Roost trees (n = 50) typically were tall, dead, large-diameter trees with exfoliating bark, located at low elevations and close to water. Trees surrounding roosts typically were smaller in diameter and shorter in height, but they had greater soundness than the roost trees. We documented 14 home ranges in areas of diverse, patchy land cover types that were close to water with east-facing aspects. Across all landscape extents, area of forest within roost-tree buffers and the aspect across those buffers were the most consistent features. Predictive maps indicated that suitable habitat ranged from 4.7–8.1% of the area examined within the Champlain Valley. These habitat models further understanding of Indiana bat summer habitat by indicating minimum habitat characteristics at multiple scales and can be used to aid management decisions by highlighting potential habitat. Nonetheless, information on juvenile production and recruitment is lacking; therefore, assessments of Indiana bat habitat quality in the region are still incomplete.

Segregation of Beaufort Sea beluga whales during the open-water season

Population segregation by habitat use occurs because energy requirements and survival strategies vary with age, sex, size, and reproductive stage. From late summer to early fall in 1993, 1995, and 1997, relative length (age), sex, and reproductive status of satellite-tagged beluga whales ( Delphinapterus leucas (Pallas, 1776)) in the eastern Beaufort Sea were tested for habitat segregation. We used (i) resource selection function models to evaluate how belugas used areas of varying sea ice concentration and shelf habitat and (ii) distance analysis to measure the selection of areas varying in distance to mainland and island coastlines. Resource selection functions and distance analysis established that habitat selection differed with length, sex, and reproductive status of whales: (i) females with calves and smaller males selected open-water habitats near the mainland; (ii) large males selected closed sea ice cover in and near the Arctic Archipelago; and (iii) smaller males and two females with calves (not newborn) selected habitat near the ice edge. The segregation of habitat use according to sex, age, and reproductive status relates to the different resources required at different life stages and may represent characteristics of beluga social structure. We discuss our results in the context of two common sexual segregation hypotheses and conclude that summer habitat segregation of belugas reflects differences in foraging ecology, risk of predation, and reproduction.

Clonal regeneration of an arrow bamboo, Fargesia qinlingensis, following giant panda herbivory

Characteristics of giant panda herbivory sites and clonal regeneration of an arrow bamboo Fargesia qinlingensis following giant panda grazing were studied in the Qinling Mountains of China. Three types of plots were located in a pandas’ summer habitat in 2002: herbivory (naturally grazed by giant pandas), clipped (simulated panda herbivory), and control. Average area of herbivory sites was 2.92 m2 and average distance from herbivory sites to the closest tree (dbh > 10 cm) was 1.0 m. Pandas avoided thin bamboo culms with basal diameters <5 mm. Average height of stumps of culms grazed by panda was 0.67 m and average density of grazed culms was 9.0 culms m−2. Annual culm mortality rate was significantly greater in herbivory and clipped plots than in control plots while annual recruitment rate was not significantly different among the three plot types in 2003. Neither recruitment rate nor mortality rate were significantly different among the three plot types in 2004. Annual recruitment rate was significantly greater than annual mortality rate only in control plots in both 2003 and 2004, suggesting static ramet dynamics in disturbed plots (herbivory and clipped). Density of new shoots was not significantly different, but basal diameter of new shoots was significantly less in herbivory plots compared to control plots in 2002. Differences of annual mortality rate and growth of new shoots found between control plots and herbivory plots suggest that clonal regeneration of F. qinlingensis culms was negatively affected by giant panda grazing. Therefore, no evidence of a clonal integration compensatory response to panda herbivory was found in F. qinlingensis.

Gunnison Sage-Grouse Use of Conservation Reserve Program Fields in Utah and Response to Emergency Grazing: A Preliminary Evaluation

Little information is available on the use of areas enrolled in the Conservation Reserve Program (CRP) by Gunnison sage-grouse (Centrocercus minimus) or the impacts of grazing on their habitat selection and movement patterns. Using radiotelemetry, we monitored 13 Gunnison sage-grouse in San Juan County, Utah, USA during 2001–2002 to determine their use of CRP. Additionally, in 2002 some of the CRP land used by the birds in 2001 was grazed under a drought emergency declaration. This afforded us an opportunity to monitor their response to livestock grazing. Although Gunnison sage-grouse used CRP for nesting, brood-rearing, and summer habitat, it was not selected in greater proportion than its availability (P ≤ 0.10) on the landscape. Bird-use sites in the CRP did not entirely meet habitat guidelines recommended by the Gunnison sage-grouse Rangewide Steering Committee (2005). Most of the sage-grouse we monitored avoided CRP fields when livestock were present. The one exception to this was a hen with a brood. We believe long-term maintenance of CRP in San Juan County will result in achieving habitat conditions that are more desirable for Gunnison sage-grouse. Future livestock management practices in areas used by Gunnison sage-grouse should incorporate short-term, high-intensity deferred-grazing rotations.

Summer Habitat Use by Snowshoe Hare and Mountain Cottontail at Their Southern Zone of Sympatry

The snowshoe hare (Lepus americanus) is a habitat specialist with a broad geographic range associated with boreal and subalpine forests in North America (Hall 1981, Hodges 1999a,b). It reaches southern range limits in the Southern Rocky Mountains in northern New Mexico, USA. Here, scant and mostly anecdotal evidence suggests that it is restricted to high-elevation, subalpine conifer forests dominated by Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa; Findley et al. 1975, DeVelice et al. 1986, Pase and Brown 1994). These southwestern forests lack several plant species, including lodgepole pine (Pinus contorta), jackpine (Pinus banksiana), black spruce (Picea mariana), birch (Betula spp.), and balsam poplar (Populus balsamifera), that, in more northern latitudes, are considered important habitat elements for snowshoe hare, especially in terms of cover (Bittner and Rongstad 1982, Litvaitis et al. 1985, DeVelice et al. 1986, Ferron and Ouellet 1992, Bryant et al. 1994, Pase and Brown 1994, Moir and Fletcher 1996). Methods for managing subalpine forests for snowshoe hare in the Southern Rocky Mountains are particularly important because of a current effort to reintroduce Canada lynx (Lynx canadensis), which is a specialized predator of snowshoe hare (Hodges 1999a,b, Colorado Division of Wildlife 2002). Another leporid, the mountain cottontail (Sylvilagus nuttallii), occurs throughout the intermountain region of western North America, also reaching the southern extent of its range in the American Southwest (Hall 1981). Throughout this broad zone of sympatry, the two leporids segregate in ecological distribution with no reports of syntopy (Bittner and Rongstad 1982, Chapman et al. 1982, Chapman and Wilner 1986). The mountain cottontail typically is associated with lower-elevation sagebrush (Artemisia spp.)–dominated habitats (Orr 1940, Chapman 1975, 1999, Chapman et al. 1982). However, it is a habitat generalist and at more southern latitudes it also occurs in higher-elevation habitats including juniper (Juniperus spp.) and pinon pine (Pinus spp.) woodlands and middle-elevation montane conifer forests, which are dominated by ponderosa pine (Pinus ponderosa), white fir (Abies concolor), Douglas-fir (Pseudotsuga menziesii), and blue spruce (Picea pungens; Bailey 1931, Durrant 1952, Findley et al. 1975, Hoffmeister 1986, Fitzgerald et al. 1994, Frey and Yates 1996). Mountain cottontails also occur in subalpine conifer forest in areas of the Southwest and Southern Rocky Mountains where snowshoe hare are absent, such as the White Mountains in eastcentral Arizona and the Pikes Peak massive in central Colorado (Warren 1910, Armstrong 1972, Hoffmeister 1986). Findley et al. (1975) reported a specimen each of mountain cottontail and snowshoe hare from Goose Lake, Taos County, New Mexico, USA. This locality is at 3,542 m elevation, which is in the subalpine conifer forest zone. These records suggested that less ecological segregation between snowshoe hare and mountain cottontail might occur in the American Southwest, including the potential for local syntopy. Thus, the purpose of our study was to assess habitat use of snowshoe hare and mountain cottontail in subalpine conifer forests at their southern point of sympatry in the Southern Rocky Mountains.

Habitat use by a Midwestern U.S.A. riverine fish assemblage: effects of season, water temperature and river discharge

The hypothesis that temperate stream fishes alter habitat use in response to changing water temperature and stream discharge was evaluated over a 1 year period in the Neosho River, Kansas, U.S.A. at two spatial scales. Winter patterns differed from those of all other seasons, with shallower water used less frequently, and low‐flow habitat more frequently, than at other times. Non‐random habitat use was more frequent at the point scale (4·5 m2) than at the larger reach scale (20–40 m), although patterns at both scales were similar. Relative to available habitats, assemblages used shallower, swifter‐flowing water as temperature increased, and shallower, slower‐flowing water as river discharge increased. River discharge had a stronger effect on assemblage habitat use than water temperature. Proportion of juveniles in the assemblage did not have a significant effect. This study suggests that many riverine fishes shift habitats in response to changing environmental conditions, and supports, at the assemblage level, the paradigm of lotic fishes switching from shallower, high‐velocity habitats in summer to deeper, low‐velocity habitats in winter, and of using shallower, low‐velocity habitats during periods of high discharge. Results also indicate that different species within temperate river fish assemblages show similar habitat use patterns at multiple scales in response to environmental gradients, but that non‐random use of available habitats is more frequent at small scales.

Birds in willow short‐rotation coppice compared to other arable crops in central England and a review of bird census data from energy crops in the UK

We present the results of spring and winter surveys of birds using 22 willow short‐rotation coppice (SRC) fields and 22 paired arable or grassland controls over a 5 year period in central and northern England. The study sites were linked to the first commercial wood‐fuelled electricity plant in Yorkshire and were managed commercially. We use the findings of this study, in the context of other work on birds in energy crops, to suggest how birds may be affected by commercial cropping of SRC or energy grasses on UK farmland. For willow SRC, most existing farmland species were not completely displaced by SRC cropping. Even farmland specialists such as Skylark Alauda arvensis used cut SRC fields. Some species characteristic of scrub and wood‐type habitats were attracted onto farmland by SRC. Birds were more abundant in hedgerows next to SRC than in those adjoining arable or grass. The interior of large SRC plots contained fewer birds than the edge‐zone (&lt; 50 m). In winter, the same resident species occured in SRC as the summer, plus winter migrants such as Snipe Gallinago gallinago and Fieldfare Turdus pilaris. Overall, more individuals and species were recorded in and around SRC than equivalent arable or grassland throughout the year. Yellow Wagtail Motacilla flava and certain locally occurring farmland specialists may be displaced by SRC plantations. Equivalent census data for energy grasses in the UK are not available. The impact of large regional energy crop developments on birds is not known. We do not know if species commonly recorded in these crops survive and breed well so population effects are unknown. However SRC crops are often weedy and insect rich and hence have potential as foraging habitats in summer and winter. The scope for agri‐environment schemes to include energy crops is discussed.

Migrations of soufie (Leuciscus souffia agassizii, VAL. 1844) in a natural river and a tributary determined by mark-recapture

From April to October 1998, soufie (Leuciscus souffia agassizii, VAL. 1844) were fished monthly using electrofishing at four sampling sites in the Argen River and in a little tributary. All fish with a body size exceeding 8 cm were tagged individually using micro tags. Additionally the fish were tagged according to sampling site by jet injection using Alcian Blue dye. The main part of the soufie population exhibited a migratory behaviour during the year between winter and summer habitat. Most of the soufie overwintered in a pool of a little tributary of the river, whereas age 0 + soufie remained in the river for the whole year. After spawning in spring in the river, the fish segregated during summer for feeding in the main river system. In the autumn, the fish returned to their winter habitat. It is concluded that the tributary plays an important role as overwintering habitat for the soufie population (except 0 +) of the investigated river section.

Habitat use by the European polecat Mustela putorius at low density in a fragmented landscape

We studied habitat use and selection, seasonal variation in the use of different habitats, and the factors possibly influencing their utilisation in six male and four female polecats Mustela putorius monitored in a fragmented area in Luxembourg. Deciduous forests appeared to be the most used habitat in summer, whereas grassland and pastures were more often used in winter and spring. Human settlements were frequently used in winter, likely because they provide both food and insulation. The influence of climatic conditions on habitat use was assessed; both rain and temperatures seemed to affect habitat use by polecats. Food habits also showed a seasonal variation with small rodents as the main food item in all seasons, but with amphibians becoming an important prey in spring and summer. Our results suggest that habitat use is influenced by trophic factors and climatic conditions, which confirms the opportunistic feeding behaviour of the polecat.

Gulf sturgeon summer habitat use and fall migration in the Pascagoula River, Mississippi, USA

The locations and habitat features of freshwater holding areas and the timing of fall migration are undocumented for Gulf sturgeon in the Pascagoula River drainage, Mississippi. Our objectives were to identify and characterize holding areas for Gulf sturgeon (Acipenser oxyrinchus desotoi), document their summer and fall movement patterns, and determine migration cues. To do this we captured, radio-tagged, and monitored movement of Gulf sturgeon in the Pascagoula River drainage and analyzed these data using geographic information systems. From May to November Gulf sturgeon congregate in a holding area in the lower portion of the Pascagoula River and Big Black Creek [river kilometers (rkm) 57–68] and near Cumbest Bluff (rkm 40), before they return to the Gulf of Mexico. While in the holding area, Gulf sturgeon were typically found in deep locations, either in or downstream from river bends. As found in other rivers, Gulf sturgeon in the Pascagoula River showed little movement within the holding area and often stayed within a single river bend; although we observed local movements by some individuals (under 10 rkm). In the Pascagoula River, Gulf sturgeon initiated their migration out of fresh water from late-September to mid-October, coincident with shorter day length, falling water temperature (mean = 23.7°C, range 21–26°C), and elevated river flow. Our work demonstrates that the lower Pascagoula River serves as a vital area for Gulf sturgeon.

Hierarchical habitat selection by North American porcupines in southern boreal forest

In habitat-selection studies, a multi-scale approach is considered necessary to ensure that all elements of selection are depicted and that management decisions accurately reflect the needs of the species under study. We examined hierarchy in summer habitat selection in North American porcupines (Erethizon dorsatum (L., 1758)) in Eastern Canada at the scales of landscape, home range, and single tree. We used radiotelemetry to locate and observe animals visually to record their behaviour and exact location in the habitat. Den use in summer was unexpectedly high for some of our animals, which forced us to use a restricted number of locations per individual for comparison among scales. Although porcupines are generalists at the landscape level, selection patterns appear at the home-range and tree levels. Human-used land and conifer forests were least selected features of home ranges, while deciduous forests dominated by trembling aspen (Populus tremuloides Michx.) and mixed forests were most selected. At the tree scale, trembling aspen was found to be selected over other deciduous trees. However, fruit-producing trees were even more selected. This study shows the importance of a multi-scale approach that includes fine-scale selection.

Sex‐related differences in roost‐site selection by Daubenton's batsMyotis daubentoniiduring the nursery period

1 We investigated sex-related differences in roost-site selection by Daubenton's bats Myotis daubentonii in their summer habitat in central Germany. We studied whether the location of and landscape structure around nine nursery roosts and seven male-only roosts differed during the nursery period (15 May−31 July). Roosts were located by radio-tracking, and animal numbers and group composition were obtained by trapping and counting at roosts. Landscape structure was evaluated by a GIS-based habitat analysis. 2 Marked variation in animal numbers was observed both in nursery roosts (range: 6–144 individuals) and male roosts (range: 1–51 individuals). The surroundings of nursery and male roosts varied significantly in the proportion of areas belonging to different landscape elements. The areas covered by ponds, lakes and rivers, as well as the area covered by coppices were larger in the surroundings of nursery roosts. Moreover, nursery roosts lay closer to a river and at lower altitudes than male roosts. Male Daubenton's bats used more distant foraging sites than gravid or lactating females. 3 The differences in roost-site location between the two sexes are suggestive of intraspecific competition for access to productive foraging areas in the surroundings of the summer roosts, with females being dominant over males. We assume that breeding females defend climatically favourable areas with good food supply in order to increase the survival of their offspring.

Summer habitat relationships of barbels in south‐west Spain

An analysis was made of the associations with local habitat features of barbels (Barbus sp.) of a Mediterranean river basin. The analysis was based on the presence data from sampling the upper, middle, and lower reaches of 31 rivers in the middle Guadiana River basin (south‐west Spain). Numerous local habitat variables were determined, including the river's size and substratum, physicochemical variables of water, and the aquatic and riparian vegetation. For each species, a univariate analysis was performed using preference indices, and logistic regression was used to construct a parsimonious multivariate model and Gaussian response models with the most influential variables, quantifying the species’ limits of tolerance. Distinct habitat associations for every species were obtained, mainly relating Barbus comiza to the larger habitats and higher water levels, Barbus microcephalus to the maintenance of lotic conditions and Barbus sclateri to more fluctuating rivers. Barbus steindachneri showed a different habitat relationship from that of the genetically almost identical B. comiza. Cover played a significant role in all but B. comiza.

Into thin air: vertical migration, body condition, and quality of terrestrial habitats of alpine common toads, Bufo bufo

Since the end of the 1980s there has been increasing evidence of worldwide amphibian declines in high-altitude regions. Moreover, amphibian conservation has so far mostly neglected the terrestrial habitat, which is essential for effective protection measures. We determined the location and quality of terrestrial habitats of common toads (Bufo bufo L., 1758) in a naturally fragmented alpine environment (Schlumsee, 1105 m a.s.l., Northern Calcareous Alps, Austria) characterized by a high diversity of available microhabitats. By radio-tracking 18 individuals during their post-spawning migration, we located terrestrial habitats 130–1000 m horizontally away from and 85–390 m above the breeding site. This is the first study to show vertical migration over several hundred metres in adult amphibians. Both adult and juvenile toads completed the migration within 2–7 weeks and, on their way to the summer habitat, climbed 45° scree slopes and ascended cliffs with slopes of up to 65°. Body condition indices were highest for individuals originating from the terrestrial summer habitat at the highest elevation, which is characterized by the highest vegetation diversity, a high abundance of food, and the highest insolation, probably allowing the toads to extend their activity period for food intake. Our study suggests that under demanding climatic conditions it can pay off for toads to undertake costly migrations to reach high-quality habitats. For amphibian conservation, high-value habitat patches need to be located and investigated to increase the effectiveness of protection measures.

Modeling spatial and temporal variation of suitable nursery habitats for Atlantic sturgeon in the Chesapeake Bay

For rare and endangered species, bioenergetics modeling can represent a valuable approach for understanding issues of habitat value and connectivity among potential habitats within nurseries in restoration programs. We used multivariable bioenergetics and survival models for Atlantic sturgeon to generate spatially explicit maps of potential production in the Chesapeake Bay. For the period 1993–2002, spatial and temporal patterns in water quality effects (temperature, dissolved oxygen [DO] and salinity) on potential production were evaluated. In addition, two forecasted scenarios were modeled: one implementing newly revised U.S. Environmental Protection Agency (EPA) DO-criteria for the Chesapeake Bay, and the other assuming a bay-wide increase of 1 °C due to an underlying trend in regional climate. Atlantic sturgeon's low (survival/growth) tolerance to temperatures >28 °C was a critical constraint during their first 1–2 summers of life. Hatched in freshwater (spring to mid-summer), young-of-the-year were predicted to occupy cooler (deeper) areas as temperature approached sub-lethal levels. While most thermal refuges were located down-estuary, a large fraction of potential refuges were unsuitable due to persistent hypoxia and/or salinity levels beyond the limited osmoregulatory capabilities of early juvenile Atlantic sturgeon. As a result, suitable summer habitats for juvenile Atlantic sturgeons in the Chesapeake Bay were predicted to be spatially restricted and variable between years, ranging from 0 to 35% of the modeled bay surface area. In critical (drought) years, almost no summer habitat was predicted to be available for juvenile Atlantic sturgeon. Value and size of nursery habitat was highly sensitive to climatic oscillations and anthropogenic interventions affecting freshwater inflow, water temperature and/or DO. Achieving EPA DO-criteria for the Chesapeake Bay was predicted to increase total suitable habitat by 13% for an average year, while increasing water temperature by just 1 °C bay-wide would reduce suitable habitat by 65%.

Uncoupling strong predator–prey interactions in streams: the role of marginal macrophytes

Predation refugia can facilitate the coexistence of predators and prey within an ecosystem by weakening trophic links between the two. The marginal macrophytes of shallow lakes are used facultatively by zooplankton to escape fish predation, leading to the stabilisation of lentic food webs. Little is known about such a role for the marginal macrophytes of lotic systems. In this paper, we examine whether the marginal macrophytes of chalk streams help buffer the interaction between the freshwater shrimp, Gammarus pulex and a benthic fish predator, Cottus gobio, both characteristically abundant in such systems.Quantitative surveys were taken of Gammarus and bullheads in winter and summer in a southern English chalk stream. These indicated that Gammarus seasonally switched their habitat preference, from marginal macrophytes in summer, to midchannel habitats in winter. Bullheads exhibited an opposite trend, preferring midchannel habitats in summer and all habitats, particularly marginal macrophytes, in winter. Large Gammarus and precopula pairs were found almost exclusively in the margins in summer. This spatial separation between Gammarus and bullheads in summer, though not in winter, was reflected in bullhead diets, as determined by gut analysis.In field manipulation experiments, bullhead presence was the strongest factor explaining the between‐habitat distribution of Gammarus in both summer and winter, indicating that the habitat shift of Gammarus was driven by the distribution of fish. Other abundant invertebrate taxa, including Asellus, mayflies and chironomids, exhibited little avoidance of habitat patches of high bullhead density.We conclude that marginal macrophytes in chalk streams can potentially facilitate the coexistence of high densities of both Gammarus and bullheads by spatially separating predator and prey in summer. They may further allow large populations of Gammarus to persist in the presence of high bullhead density at stretch‐wide spatial scales, by reducing the predation by bullheads of large breeding and newly born individuals of Gammarus in summer.

Linkages between weather, dissolved organic carbon, and cold-water habitat in a Boreal Shield lake recovering from acidification

To investigate potential effects of climate change on lake thermal structure, we examined relationships between the amount of cold-water habitat in late summer (defined as the 10 °C depth), summer weather, and dissolved organic carbon (DOC) concentration over a two-decade period (1981–2002) in a small Boreal Shield lake recovering from acidification. DOC concentration, wind-days (the product of mean daily wind speed and the number of days between ice-out and late-summer stratification), and mean daily temperature were significant predictors of the 10 °C depth in a multiple-regression model. A similar model using simply the number of ice-free days instead of wind-days was almost as effective. The models were quite successful in explaining interannual variations in the 10 °C depth when tested on a chemically and morphometrically similar nearby lake. While factors related to summer weather were important in explaining interannual variations in the amount of late-summer cold-water habitat, increased DOC concentration over the study period largely explained observed long-term decreases in the 10 °C depth (increases in cold-water habitat). DOC concentration was positively correlated with pH. In acidified regions, increases in DOC that accompany the recovery of acidified lakes will need to be considered in assessments of potential climate-change effects on lake thermal structure.

Habitat use by the hymenosomatid crab Amarinus lacustris (Chilton) in two south-eastern Australian rivers

The hymenosomatid crab Amarinus lacustris is abundant in some south-eastern Australian rivers; however, little is known of its ecology. Patterns of habitat use by crabs in rivers may be affected by seasonal changes in river discharge. This study investigates population characteristics, timing of reproduction and patterns of habitat use by A. lacustris in five riffle and pool habitats from each of the Hopkins and Merri Rivers in south-west Victoria, Australia, sampled over a twelve-month period. Distribution of Amarinus lacustris was similar between the two rivers, but log-linear modelling showed that there was a strong association between crab sex, habitat occupied and time of year because female A. lacustris showed a shift from riffle to pool habitats during March and April, coinciding with the non-gravid period of the year. Male crabs also showed a change in relative occurrence, occurring most often in riffles during winter–spring (July–November) but being equally common in both habitats in summer–autumn (January–May). These patterns are probably the result of the reproductive cycle of A. lacustris, which appears to show both ontogenetic and sex-related changes in habitat use during its life cycle, taking advantage of seasonal fluctuations in flow regime that may assist egg/larval development and dispersal.