Differences In Habitat Utilization Research Articles

Potential Effects of Habitat Change on Migratory Bird Movements and Avian Influenza Transmission in the East Asian-Australasian Flyway

Wild waterbirds, and especially wild waterfowl, are considered to be a reservoir for avian influenza viruses, with transmission likely occurring at the agricultural-wildlife interface. In the past few decades, avian influenza has repeatedly emerged in China along the East Asian-Australasian Flyway (EAAF), where extensive habitat conversion has occurred. Rapid environmental changes in the EAAF, especially distributional changes in rice paddy agriculture, have the potential to affect both the movements of wild migratory birds and the likelihood of spillover at the agricultural-wildlife interface. To begin to understand the potential implications such changes may have on waterfowl and disease transmission risk, we created dynamic Brownian Bridge Movement Models (dBBMM) based on waterfowl telemetry data. We used these dBBMM models to create hypothetical scenarios that would predict likely changes in waterfowl distribution relative to recent changes in rice distribution quantified through remote sensing. Our models examined a range of responses in which increased availability of rice paddies would drive increased use by waterfowl and decreased availability would result in decreased use, predicted from empirical data. Results from our scenarios suggested that in southeast China, relatively small decreases in rice agriculture could lead to dramatic loss of stopover habitat, and in northeast China, increases in rice paddies should provide new areas that can be used by waterfowl. Finally, we explored the implications of how such scenarios of changing waterfowl distribution may affect the potential for avian influenza transmission. Our results provide advance understanding of changing disease transmission threats by incorporating real-world data that predicts differences in habitat utilization by migratory birds over time.

Movements, habitat utilization, and post-release survival of cobia (Rachycentron canadum) that summer in Virginia waters assessed using pop-up satellite archival tags

BackgroundCobia (Rachycentron canadum) is a cosmopolitan marine fish that inhabits tropical, sub-tropical, and temperate marine and estuarine waters and supports a major recreational fishery along the U.S. Atlantic and Gulf of Mexico coasts. Recent changes in U.S. cobia management have sparked controversy and highlighted limitations in our understanding of the species’ biology. This study utilized pop-up satellite archival tags (PSATs) to assess the movements, habitat utilization, and post-release survival of cobia that summer in Virginia waters.ResultsPSATs were deployed on 36 cobia caught in Virginia state waters using standard recreational techniques in August 2016 and August–September 2017. All fish larger than 37-in total length were tagged, and several of these were hooked deeply. No mortalities were inferred for the 20 cobia whose PSATs reported and remained attached for at least 10 days. Premature release of tags was an issue, and only five PSATs remained attached for the full 180-day deployment period. Some fish undertook long seasonal movements, with one individual entering Florida waters well beyond the current stock demarcation boundary. Several fish overwintered in waters offshore of North Carolina near the continental shelf break. Cobia demonstrated a strong affinity for waters ≥ 20 °C, even in the coldest months. They displayed distinct seasonal differences in habitat utilization, spending high proportions of their time near the surface during the summer months and extended periods at depths ≥ 20 m in the winter months.ConclusionsCobia are hardy fish with low post-release mortality when handled respectfully. Their migratory patterns are clearly temperature driven, and seasonal changes in habitat utilization means varied vulnerability to fishing gears. Further understanding of cobia migratory patterns, particularly in conjunction with spawning activity, is needed to best manage this species.

Morphological and ecological divergence in two populations of European glass lizard, Pseudopus apodus (Squamata: Anguidae).

The European glass lizard, Pseudopus apodus (Pallas, 1775), is a large, legless lizard with wide distribution across south-eastern Europe and eastern and central Asia. To date, morphological diversification among populations on a geographically small scale has not yet been reported in this lizard. Thus, we investigated the morphological variations and corresponding differences in habitat utilization between two populations of P. apodus inhabiting the same biogeographical zone within a relatively close geographic area. We hypothesized that minor differences in habitat could induce a significant level of morphological differentiation, thus indicating morphological plasticity in this species on a small geographical scale. We sampled 164 individuals (92 from the Croatian mainland and 72 from the island of Cres). Results showed that P. apodus indeed exhibited morphological differences between populations in the same biogeographical zone within a relatively close geographic area, with the Cres Island individuals being generally larger than the individuals from the mainland. Some ecological characteristics were similar in both populations (e.g., soil temperature, distance to hiding place), whereas others were distinct (e.g., air temperature and humidity). In addition, vegetation cover differed between the two sites, with more vegetation present on the mainland than on the island. Furthermore, the Cres Island population showed clear sexual dimorphism, which was absent in the mainland population.

Visually Guided Search Behavior during Walking in Insects with Different Habitat Utilization Strategies

This review examines visually guided search behavior during walking in different species and developmental stages of insects having contrasting habitat utilization strategies. The discussion focuses on mantises, short-horned grasshoppers and crickets. Although generally short-horned grasshoppers are travelers, whereas mantises are ambush predators, all of these insects exhibit visually guided behavior during walking in the search for food sites and shelter. In crickets, which are central place foragers, visually guided behavior during walking is also important for nest site homing. Despite differences in habitat utilization, these three insect groups all use searches incorporating intermittent locomotion, where the distances traveled and duration of pauses have a distinct functional significance. However, there are also locomotion pattern variations, such as loops, zigzags, spiral patterns and straight lines. Search strategies during walking include searches with and without visual landmarks. The detection and recognition of stationary visual landmarks is based on self-induced retinal image displacement, with differing underlying neuronal mechanisms in the three insect groups. If a visual landmark is identified as a suitable target, a direct approach is elicited under either open- or closed-loop conditions, depending on the situation. In the presence of more than one suitable target object, the behavioral response can be temporarily restricted to stimuli associated with a particular area of the visual field, while information from other areas of the visual field is suppressed. The review concludes that there are gaps in knowledge concerning the various questions and thus further research is needed.

Paedophagic cannibalism, resource partitioning, and ontogenetic habitat use in an invasive lizard

Various aspects of social structure can be important drivers of basic behavioral patterns, including dispersal, intraspecific niche partitioning, and resource utilization. Juvenile–adult interactions such as agonistic displays and paedophagic cannibalism can result in avoidance of adults by juveniles, and can influence community structure via shifts in ontogenetic habitat use patterns and juvenile dispersal. In this study, we examined the role of agonistic behavior in determining differences in habitat utilization between life stages in an ecologically damaging invasive lizard, Trioceros jacksonii xantholophus, in the Hawaiian Islands. We tested the hypothesis that intraspecific aggression by adults drives observed niche separation and juvenile dispersal. In the laboratory, we conducted paired conspecific trials to assess paedophagic behavior, and staged contests to assess aggression and response: 57% of adults consumed newborns when paired. In addition, juveniles fled further, faster, and more often in response to aggressive adult displays than from other juveniles. To assess the effect of antagonistic behaviors on juvenile movement and its potential role in and habitat shifts, we used radio-telemetry and exploited diet comparison to assess resource use in juveniles versus adults. Though our results suggested no significant difference in immature versus adult chameleon dispersal, juveniles were found to perch at significantly lower heights above ground, and exploited different prey types than did adults. These results suggest that resource partitioning is occurring, but the immature chameleons are sedentary as are the adults. Due to age-dependent habitat usage, our results suggest that T. j. xantholophus occupies a broader niche than previously recognized. These results highlight the importance of studies focused on patterns of behavior at different developmental stages of invasive species, which ultimately provide better information allowing prediction of ecological impacts and range expansion potential.

Polynuclear Aromatic Hydrocarbons in Port Valdez Shrimp and Sediment.

Polynuclear aromatic hydrocarbons (PAHs) from oil were present in some shrimp from Port Valdez, site of a ballast water treatment facility at the Alyeska Alaska Marine Terminal (AMT). Low-level petrogenic PAH concentrations were generally restricted to shrimp eggs in the vicinity of the AMT and extended along the southern shore of Port Valdez to Anderson Bay. Eggs had greater lipid content than other tissues and thus were the most vulnerable biological compartment to hydrocarbon accumulation. Petrogenic hydrocarbons were not observed in shrimp muscle and cephalothoraxes; thus, these tissues do not pose a human health risk. Risk for children older than age 2 years and adults consuming eggs also was low except for two unusual samples (of 32), collected about 17 km west of the treatment facility. In general, PAH loads were consistent with local time series data in other species. We infer that the accumulation mechanism was dissolved uptake from water, consistent with passive sampler observations completed more than a decade earlier. Hydrocarbon levels in the majority of samples were below toxic thresholds. Total PAH accumulation was substantially greater in some pink shrimp than in other species, thus differences in habitat utilization (muddy vs. rocky substrate) are potentially important.Electronic supplementary materialThe online version of this article (doi:10.1007/s00244-016-0279-3) contains supplementary material, which is available to authorized users.

Habitat use patterns and food habits of the Kashmir red deer or Hangul (Cervus elaphus hanglu) in Dachigam National Park, Kashmir, India

The last surviving wild population of the Kashmir red deer (Cervus elaphus hanglu) or Hangul inhabits the Dachigam National Park located near Srinagar city of Kashmir, India. This paper presents data from February 2001 to December 2009 on habitat use patterns and food habits of the Kashmir red deer. Investigations based on surveys along trails indicate that Hangul showed significant differences in the use of different habitat types (F = 6.49; P = 0.001) between seasons. Males showed significant differences in habitat utilization both within a season (F = 3.63; P ≤ 0.013) and between seasons (F = 1.50; P ≤ 0.087). Females showed differences in their habitat use within season but not between seasons (F = 14.771; P ≤ 0.577). Surveys showed the deer predominantly using the lower and middle altitudes (1700–1900 m and 1900–2300 m) with no significant gender differences. The riverine and mixed oak forests showed the highest mean deer pellet density/ha (153.71 ± 173.43, n = 418 and 188.60 ± 56.41, n = 114, respectively). The grassy/rocky cliff habitat showed the lowest mean pellet density/ha (55.92 ± 18.32, n = 228). The Hangul diet constituted mainly of dicotyledonous shrubs and trees (45.45 and 80.77%), forbs/herbs (36.36 and 19.23%), monocotyledon grasses and herbs (18.18 and 16.22%) in spring and winter, respectively. Summer diet comprised 42.86% forbs, 19.05% grass/sedges and 38.10% browses. In autumn, Hangul fed mainly on dicotyledonous shrubs. The habitat use patterns of Hangul are comparable with those of the European red deer and are influenced by availability of food, cover, shelter, altitude, slope, aspect and the level of disturbance. The habitats with ideal conditions for utilization but with a meager disturbance were avoided by Hangul. Recommendations are given for better and effective management, protection and conservation of this small and isolated population of red deer.

Discordant patterns of genetic connectivity between two sympatric species, Mullus barbatus (Linnaeus, 1758) and Mullus surmuletus (Linnaeus, 1758), in south-western Mediterranean Sea

Population connectivity scales are important tools to achieve a mechanistic understanding of the factors regulating the abundance and distribution of marine populations and therefore support conservation actions to manage fisheries and stocks. We used 10 microsatellites markers on mullets' samples across the Spanish coast to determine the spatial scale of gene flow as well as the origin of post-larvae caught inside two MPAs. Population structure varied from complete homogeneity for Mullus barbatus, to high spatial variability in Mullus surmuletus samples. Differential habitat utilization by species, geomorphological features and oceanographic patterns are discussed as potential causes of patterns observed. Although we were unable to verify the origin of most post-larvae caught inside MPAs we suggest that they may act as genetic reservoirs due to high heterozigosity levels found in adult specimens inside (M. surmuletus) and nearby (both) them. Our results indicate that early life history traits (i.e. larvae) may not be the only determinant on species dispersal capability, suggesting that other mechanisms such as fine scale adult or juvenile movement may have been underestimated as promoting population connectivity.

Seasonal rhythm in a Mediterranean coastal fish community as monitored by a cabled observatory

To adequately describe seasonal rhythms in habitat utilization by fish communities, observations are needed that occur at a relatively high frequency and over large temporal windows. For the first time, images col- lected from a cabled video-observatory (the western Mediterranean expandable SEAfloor OBservatory; OB- SEA) were utilized to examine habitat utilization by coastal fishes. Over the course of a year, hourly digital images of the water column and an artificial reef were obtained dur- ing daylight hours. For each image, the total number of species, an estimate of the abundance of individuals, and the Shannon Diversity Index were quantified. A total of 22 fish species commonly associated with nearshore western Mediterranean habitats were identified, and significant spatial (water column vs. artificial reef), seasonal (spring, summer, autumn, and winter), and daily (morning, midday, and sunset) differences in habitat utilization occurred. Four species (Diplodus vulgaris, Diplodus cervinus, Diplodus sargus, and Scorpaena porcus) were associated with the artificial reef, while one species (Pagrus pagrus) chiefly occurred in the water column. Chromis chromis and Diplodus annularis occurred at the site more frequently in the winter and autumn, respectively, while 14 other species utilized the site more frequently in either the spring (8 spp) or summer (6 spp). In addition, Dentex dentex and Spicara maena occurred more frequently at sunset, while D. cer- vinus displayed a crepuscular rhythm (occurring more frequently in the morning and at sunset). Species diversity was highest in the summer and lowest in the winter. If not taken into account when planning in situ sampling, such seasonal and/or diel differences may lead to spurious estimates of population sizes and biodiversity. We suggest that cabled video-observatories offer a non-invasive and reliable technology for faunistic sampling and population assessment in coastal water of the Mediterranean and likely elsewhere.

Host diversity and latitude drive trematode diversity patterns in the European freshwater fauna

Aim We investigated the relationship between host and parasite diversity as well as latitudinal gradients in parasite diversity on a continental scale in European freshwater trematodes. Location European freshwaters. Methods We extracted distributional data for 564 freshwater trematodes across 25 biogeographical regions in Europe from the Limnofauna Europaea and used multiple regression analyses to test for correlations between the diversity of definitive (vertebrates) or first intermediate (gastropods) hosts and that of trematodes, and for latitudinal gradients in trematode diversity. In particular, we investigated patterns in beta diversity among latitudinal bands and between trematode species that parasitize host groups with low (autogenic) and high (allogenic) dispersal capacity. We also tested for a latitudinal gradient in the proportional representation of these two trematode groups within regional faunas. Results Latitude or first intermediate host richness had no effect on trematode richness, but definitive host richness was a strong predictor of trematode richness, among both allogenic and autogenic parasites. We found that beta diversity of trematode faunas within latitudinal bands decreased to the north, with similar values for allogenic and autogenic trematodes. Finally, we observed an increasing proportion of autogenic species toward the north of Europe. Main conclusions The richness of definitive hosts appears to be the driver of trematode diversity at a continental scale. The latitudinal gradient in beta diversity reflects patterns observed in free-living species and probably results from recolonization in the aftermath of the ice ages. The similar beta-diversity patterns of allogenic and autogenic trematodes and the increasing proportion of autogenic trematodes with increasing latitude are surprising. We suggest that the geographical scale of our analysis or confounding factors such as differences in habitat utilization and specialization may partly explain these patterns.

Sex effect on polychlorinated biphenyl concentrations in fish: a synthesis

Polychlorinated biphenyls (PCBs) accumulate in fish primarily via food intake, and therefore, PCBs serve as a chemical tracer for food consumption. Sex differences in PCB concentrations of fish have been attributed to the following three mechanisms: (i) females losing a substantial portion of their PCB body burden during spawning and consequently their PCB concentration is considerably reduced immediately after spawning; (ii) sex differences in habitat utilization leading to sex differences in the PCB concentrations of the prey; and (iii) sex differences in gross growth efficiency, which is defined as growth divided by the amount of food consumption needed to achieve that growth. Based on my analyses and synthesis, mechanisms (i) and (ii) operate in relatively few fish populations, but can lead to mature males having PCB concentrations two to three times higher than mature female PCB concentrations. In contrast, mechanism (iii) operates in all fish populations, but typically, mechanism (iii) results in relatively modest sex differences, with mature males only between 15 and 35% higher in PCB concentration than mature females. In summary, the study of sex differences in PCB concentrations of fish has led to insights into fish behaviour and fish physiology.

Spatial distribution, activity, habitat selection of American mink (Neovison vison) and polecats (Mustela putorius) inhabiting the vicinity of eutrophic lakes in NE Poland

Invasive American mink and native polecats were live-trapped over a period of six years and radio-tracked during one winter-spring season in the lakeside habitats in NE Poland. The number of mink declined whereas number of polecats was stable during 1995–2000, however, except during one winter, mink were always more abundant in the study area than polecats. Significant differences in habitat utilization between radio-collared mink and polecats were observed. Mink moved only along the lake shoreline and showed no seasonal shift in habitat selection. In winter, polecats were most frequently located close to the lake banks, but they also stayed in barns and stables. In spring, they moved further from the lakes. There was considerable interspecies overlap of mink and polecat home ranges in February, and common use of the banks of the 500 m long unfrozen canal was recorded for 4 mink and 5 polecats. The pattern of daily activity of polecat and mink differed: mink were most active at dawn and in early morning whereas polecats at dusk and in beginning of the night. Individuals of both species coexisted in this small area at relatively high densities and to some degree exploited the same habitats, particularly in the vicinity of sites with access to open water.

Macroecological signals of species interactions in the Danish avifauna.

The role of intraspecific and interspecific interactions in structuring biotic communities at fine spatial scales is well documented, but the signature of species interactions at coarser spatial scales is unclear. We present evidence that species interactions may be a significant factor in mediating the regional assembly of the Danish avifauna. Because >95% of breeding species (n = 197) are migratory, we hypothesized that dispersal limitation would not be important and that breeding distributions would largely reflect resource availability and autecological habitat preferences. Instead, we detected a striking pattern of spatial segregation between ecologically similar species at two spatial scales with a suite of null models that factored in the spatial distribution of habitats in Denmark as well as population size and biomass of each species. Habitat utilization analyses indicated that community-wide patterns of spatial segregation could not be attributed to the patchy distribution of habitat or to gross differences in habitat utilization among ecologically similar species. We hypothesize that, when habitat patch size is limited, conspecific attraction in concert with interspecific territoriality may result in spatially segregated distributions of ecologically similar species at larger spatial scales. In the Danish avifauna, the effects of species interactions on community assembly appear pervasive and can be discerned at grain sizes up to four orders of magnitude larger than those of individual territories. These results suggest that species interactions should be incorporated into species distribution modeling algorithms designed to predict species occupancy patterns based on environmental variables.

Intersexual niche segregation in Cepero’s Ground-hopper, Tetrix ceperoi

Sexual differences in habitat preferences have been reported from a variety of animal taxa. However, the ultimate causes for this intersexual niche segregation remain poorly understood. It has been suggested that sexual dimorphism is a consequence of dimorphic niches based upon different reproductive costs and activities of the sexes. Here we provide evidence from field data to examine this hypothesis by studying the behavioral background of niche segregation in Tetrix ceperoi. Our data revealed distinct sexual differences in the substrates on which the insects perched and in the solar radiation of these locations. Males were found at brighter locations and more often on bare ground than females. Incorporation of behavioral data in our analysis showed that patches of bare ground were mainly utilized during mating behavior, in which males invested more time than females. In contrast, females spent more time resting and feeding in the vegetation. Intersexual differences in the proportion of autotomized individuals indicate that males might suffer higher predation risks. These patterns support the dimorphic niches hypothesis, which suggests that differential habitat utilization is caused by differences in the life history strategies of males and females, since males should accept a higher predation risk due to the benefits of multiple matings. Females should invest more time in gaining nutrients and energy for egg production and survival, whereas males should spend more time with searching for mates. We suggest that behavioral covariates should more often be implemented in ecological analyses, since these might have a strong explanatory power.

Distribution and abundance of fungi in the soils of Taylor Valley, Antarctica

The occurrence and distribution of culturable fungi in Taylor Valley, Antarctica was assessed in terms of soil habitat. Soil transects throughout the valley revealed differential habitat utilization between filamentous and non-filamentous (yeast and yeast-like) fungi. In addition, there were significant differences in species distribution patterns with respect to soil pH, moisture, distance from marine coastline, carbon, chlorophyll a, salinity, elevation and solar inputs. Filamentous fungal abundance is most closely associated with habitats having higher pH, and soil moistures. These close associations were not found with yeast and yeast-like fungi demonstrating that yeast and yeast-like fungi utilize a broader range of habitat. An intensive survey of the Victoria Land is necessary to gain a better understanding of their role in soil functioning and nutrient cycling processes.

Species-specific habitat distribution of coral reef fish assemblages in relation to habitat characteristics in an Okinawan coral reef

We determined the species-specific habitat associations of coral reef fishes and environmental characteristics in an Okinawan coral reef in Japan. We focused on three families (Pomacentridae, Gobiidae and Labridae) and attempted to determine differences in habitat utilization. We selected six sites along the coast of Amitori Bay, from the entrance to the innermost part, in order to cover a wide range of habitat characteristics (exposed habitat, semi-exposed habitat and sheltered habitat). The species diversity of coral assemblages was greater at the exposed and semi-exposed habitats, whereas branching coral mostly covered the sheltered habitat. The environmental factors that determine the species-specific spatial association in fishes differed among families. Both biological characteristics (coral morphology and coral species diversity) and physical characteristics (water depth and wave exposure) affected the spatial association of pomacentrids and gobiids. In contrast, physical characteristics such as substrate complexity and water depth affected the species-specific spatial association of labrid species. Further study is needed to determine the ecological factors that regulate the species-specific habitat preference in Okinawan coral reefs.

Alarm pheromone recognition in a Missouri darter assemblage

The a priori null hypotheses that responses to donor, orangethroat darter Etheostoma spectabile, johnny darter Etheostoma nigrum, logperch Percina caprodes, slenderhead darter Percina phoxocephala and blackside darter Percina maculata, extracts would be absent in the three test species, orangethroat darter, johnny darter and logperch, was rejected. This was because orangethroat and johnny darter responded with decreased activity to skin extracts derived from conspecifics and from other members of the assemblage. In contrast, logperch were notable by their lack of a detectable response to any species. Similarities and differences in habitat utilization are seen as a possible basis for these responses.

Enduring social relationships in a population of crab‐eating zorros, Cerdocyon thous, in Amazonian Brazil (Carnivora, Canidae)

Crab‐eating zorros, Cerdocyon thous, in Amazonian Brazil weighed 5.2 kg (S.D. 0.6, n= 19), exhibited no sexual dimorphism, lived in social units of 2‐5 adults of > 1 year old, and occupied territories (restricted polygons) of 532 ha (range 48‐1042 ha, n= 21). The zorros were omnivorous, fruit being the most frequent food (occurring in 57% of 72 faeces in the dry season) comprising 26.4% by volume of undigested faecal remains. Insects were frequently eaten (86%), and vertebrates rarely (15.2%). Zorros were territorial. The ranges of neighbours overlapped minimally and were very stable in configuration, both from month to month and between dry and wet seasons. Members of each social unit shared on average 88.3% of 200 × 200m grid cells within their territory. Members of male‐female breeding pairs were within 100 m of each other for 63% of the activity period, their proximity being greatest during the mating season (July‐August). Parents travelled in close company with their adult‐sized offspring, and stayed within 100 m for up to 93.3% of the activity period. Territories differed in habitat composition. Overall, zorros spent most time in wooded savanna (33.9%) and scrub (30.5%). They did not utilize habitats in direct proportion to their availability, using some more (e.g. scrub) and some less (e.g. open savanna) than expected. Habitat preferences differed between wet and dry seasons, with elevated habitats being favoured during the wet season. Individuals differed in their habitat utilization, and parents had different habitat usage to their yearling offspring; this difference was exaggerated in the dry season when the yearlings used lowlying habitats apparently disfavoured by the parents. Differences in habitat utilization between group members were least in the wet season, when widespread flooding forced the shared use of higher ground. Each of two social units larger than two individuals comprised a pair and their three adult‐sized offspring (totalling five males and one female). In three cases, a yearling daughter was present in the breeding season, but none of these bred. Non‐breeding offspring were seen frequently in the whelping area and in close company with the breeding pair's cubs. This is the first proof of group‐living in South American zorros. Five dispersal events were monitored, and revealed a ‘good neighbour’strategy in which newly formed pairs set up their territories adjoining their natal territories. In each case individuals returned intermittently to their original territory where they were in close and amicable company with their parents. One male, having dispersed, returned home frequently without his mate to tend the next generation of his parents’cubs. Of four dispersing males, two subsequently returned to their natal group following the deaths of their mates at least 3‐13 months after their initial dispersal, in one case after breeding elsewhere.

Differences in habitat utilization among native, native stocked, and non-native stocked brown trout (Salmo trutta) in a hydroelectric reservoir

Native and native-stocked brown trout (Salmo trutta) in Lake Tesse, a regulated hydroelectric reservoir (southern Norway), were spatially segregated according to size: small individuals occurred mainly in the epibenthic habitat and larger individuals mainly in the pelagic habitat. In contrast, all size groups of non-native stocked brown trout were mostly restricted to the epibenthic habitat. Age-specific lengths were generally larger for non-native than for native stocked trout, which were larger than native fish. However, growth rate between age 3 and 4 was significantly lower for non-native stocked fish than for native and native stocked fish. Differences in body length were mainly due to strain but also to some extent to habitat. Native fish had significantly fuller stomachs in the pelagic than in the epibenthic habitat in summer. Epibenthic non-native fish had significantly fuller stomachs than native and native stocked fish in August but not in July. Native and native stocked fish fed mainly on surface insects and planktonic crustaceans in both habitats. We hypothesize that the non-native brown trout stocked in Lake Tesse do not use the pelagic habitat in the home lake and are therefore less adapted to utilize such habitat than populations originating from lakes where pelagic habitat is available.

Differences in environmental response between the sexes of the dioecious shrub Baccharis halimifolia (Compositae)

Baccharis halimifolia (Compositae) is a dioecious shrub which grows on the upland fringe of tidal marshes along the Atlantic and Gulf Coasts of North America. We examined the responses of the two sexes to variation in nutrient and moisture availability plant density, and defoliation. By growing plants from seedlings to flowering adults under various combinations of soil type, fertilization rate and plant density, we were able to establish different rates of plant growth and mortality. Plants grown at high density and low nutrient and water supply grew the least, incurrent the most mortality and showed a male-biased sex ratio (73% male). At low density with abundant nutrients and water, plants grew more, survived well, flowered frequently, and were female-biased (75% female). Changes in sex ratio were probably the result of sex-related mortality rather than sexual lability of the seedlings. While changes in sex ratio occurred under experimental conditions in the green-house, no evidence for differences in habitat utilization between the sexes were found in the field and the sex ratio (59% female) did not vary across habitats. In the marsh habitats we sampled where water and nutrients were apparently available, there was no evidence for differential mortality between the sexes. When defoliated (75% of leaf tissue), both sexes showed similar reductions in reproductive effort (number of flower heads/shoot). Our results indicate that differences between the sexes of Baccharis in their response to environmental growing conditions is an important ecological factor associated with the separation of male and female function into separate individuals.