Between-habitat Differences Research Articles

Intrabasin variation in allometry coefficients of LenkoranCapoeta capoeta gracilis(Keyserling, 1861) in the Gorganroud basin, southeast Caspian Sea, Iran

Summary It is believed that streams of a basin may contribute to stream-specific variation in allometry coefficients related to between-habitat differences. To test intra-basin variation of the allometry coefficients of Lenkorn Capoeta capoeta gracilis (Keyserling, 1861), a total of 1731 individuals were sampled in six streams of the Gorganroud basin (southeast Caspian Sea) between April and May 2008. Values of b ranged from 2.647 for males of Chelchai to 2.964 for females of Madarsou, indicating negative allometric growth for the fish in the basin. There were variations in the allometry coefficient among the considered groups, which can be interpreted as species’ response to different habitats. To the best knowledge of the authors, this study documents the comparative reference on variation of allometry coefficient of Capoeta capoeta gracilis in southeast Caspian streams.

Habitat variation, species diversity and ecological functioning in a marine system

The expectation that long-term, broad-scale changes in the relative abundance of species, homogenisation of habitats and decreases in diversity will affect ecosystem function has led to an increasing number of studies on functional diversity and composition. Such studies frequently consider the effect of environmental gradients and anthropogenic impacts, but rarely the effect of biogenic habitat variation. In marine soft-sediment systems, habitat variability is likely to be of particular importance because of the strong link between habitat and species diversity. In this study we examine the link between functional trait diversity (as richness and evenness) and composition, and habitat variation in two locations with different regional species pools. We found similar functional traits occurring in the two locations, but differences between habitats within the locations. High evenness within traits was apparent (across both locations and habitats) reflecting the potential for the maintenance of function with the loss of individual species. Between-habitat differences in functional traits were driven by differences in organism densities rather than the presence/absence of individual traits, emphasising the importance of density shifts in driving function. Furthermore, our demonstration of habitat variation as a driver of functional composition and diversity suggests that habitat heterogeneity should be explicitly included within studies trying to predict the effect of species loss on ecosystem function.

Group foraging in the colonial spider Parawixia bistriata (Araneidae): effect of resource levels and prey size

In animal groups whose focus is on juvenile growth, prey attributes and the way in which individuals have access to those prey influence the level of sociality. Models examining the evolution of group foraging predict that, if an individual is able to monopolize a prey item, it should not permit collaboration in the capture of or feeding on that prey. If monopoly is not possible, individuals should allow others to join because of the high cost of prey defensibility. Hunger stress can affect the above predictions through its effect on the perceived value of a prey item. An increase in the individual tendency to attack prey could result in more group captures at higher hunger levels when the resident spider fails to monopolize a prey item. I conducted a study on the foraging behaviour of the colonial spider Parawixia bistriata in habitats with different insect availability. I offered prey items of known size to spiders at their web sites and determined frequency of group capture and feeding relative to prey size. I also recorded the number of individuals participating in capture and feeding groups and interactions between the resident and other foraging spiders. Individuals showed a higher tendency to capture prey and feed in a group as the size of the prey increased. In addition, spiders from habitats with lower levels of prey (dry sites) had a higher tendency to attack prey collectively than did spiders from wet sites where prey levels were higher. Although there were no between-habitat differences in tendency to feed in groups, group sizes of foraging spiders were larger at dry sites. Levels of aggression between the resident and other foraging spiders were low over all trials, but behavioural acts involving direct interactions were more frequent in groups from dry sites.

Breeding Performance of Blue Tits Cyanistes caeruleus ultramarinus in Relation to Habitat Richness of Oak Forest Patches in North-Eastern Algeria

Like many other seasonally breeding birds, Blue Tits raise their chicks mainly at the time when numerous caterpillars attack fresh oak leaves. This paper reports on the results of the first quantitative study of food ecology in combination with the breeding biology of a North African population of Blue Tits occupying distinct patches of oak habitat (high-altitude semi-evergreen zeen oak versus low-altitude evergreen cork oak). To check for between-habitat differences in intensities of nest parasites feeding on chicks, all nests monitored were heat-treated during the chickraising stage. The peak demands of the chicks were found to coincide with the peak date of caterpillar availability in both habitat types. Food availability was much higher in the semi-evergreen habitat, and the diversity of prey delivered to the chicks was higher in the evergreen habitat. Surprisingly, breeding success was very low in both habitat types. It is suggested that several environmental constraints may cause maladapted avian breeding responses in heterogeneous Algerian habitat mosaics. Spatial variation in micro-climate may influence the capacity to adaptively adjust breeding responses to distinct habitat types.

Antioxidant protection and plasma carotenoids of incubating great tits ( Parus major L.) in relation to health state and breeding conditions

Carotenoids are biologically active pigments, which are important for animals due to their dual role in health maintenance and ornamental signalling. In adult birds, immunostimulatory properties of carotenoids have been repeatedly demonstrated while much less is known about the importance of carotenoids as antioxidants. We studied the relationships between plasma carotenoid levels, as well as total antioxidant protection, and various hemato-serological health state indices in female great tits ( Parus major L.), incubating their second clutches in two contrasting (coniferous and deciduous) habitats in southwest Estonia. To manipulate reproductive effort, four eggs were removed from half of the clutches during laying to stimulate females to lay additional eggs. However, egg removal had no effect on the final number of eggs laid. Plasma carotenoid levels increased seasonally in parallel with caterpillar food availability. However, no between-habitat differences in carotenoid levels, total antioxidant capacity, or indices of health state could be found despite the apparently better feeding conditions in the coniferous habitat. No correlation was detected between plasma carotenoid levels and measures of total antioxidant capacity, which suggests that at least for the adult birds feeding on naturally carotenoid-rich diet, antioxidant function of carotenoids is not of primary importance. A strong non-linear association between the measures of antioxidant protection and leukocytic markers of inflammation was found, which suggests that measures of total antioxidant capacity deserve further attention in ecophysiological studies as potential indicators of immunopathology.

Linking taphonomy to community-level abundance: Insights into compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps)

Although actualistic live/dead comparisons lead to robust estimates of fidelity of modern death assemblages, quantitative evaluation of fidelity of fossil assemblage remains uncertain. In this paper, effects of storm reworking on compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps, Austria) are evaluated. An exploratory approach is based on comparison of reworked and non-reworked assemblages in ordination analyses. Non-reworked assemblages of one or more communities provide a baseline for evaluation of fidelity of reworked assemblages. In siliciclastic-rich intervals of the Kössen Formation, shell concentrations are represented by (1) packstones with small, shallow infaunal bivalves, (2) floatstones and pavements with large semi-infaunal bivalves, and (3) bioclastic marlstones. In carbonate-rich intervals, bioclastic floatstones with bivalves and brachiopods occur. Analyzing all shell concentrations, eight sample groups sharing similar species composition are discriminated. Limited effect of storm reworking on composition of shell concentrations is indicated by (1) a general persistence of six sample groups when only non-reworked assemblages are analyzed, (2) similarity in composition between reworked and non-reworked assemblages within sample groups, and (3) compositional segregation between non-reworked assemblages of distinctive sample groups, mostly without any reworked assemblages of intermediate composition. Depth-related variations in dead-shell production, shell destruction and body size governed preservation and distribution of the shell concentrations along onshore-offshore gradient in the Kössen Basin. First, at times when environmental conditions were unfavorable for shell producers, coupled with high background shell destruction rates, limestone beds formed during storm events were shell-poor. Second, less common shell concentrations in upper than in lower parts of siliciclastic intervals can be related to higher environmental stress in shallower habitats. Third, the difference between shell concentrations dominated by small and large bivalves is driven by between-habitat differences in body size and is not due to a differential sorting of small and large shells. Combining community analysis based on species abundances with taphonomic analysis can thus be helpful in tracking fidelity of fossil assemblages.

Reassessing the spatial relationship between sponges and macroalgae in sublittoral rocky bottoms: a descriptive approach

Because sublittoral sponges of temperate areas are usually more abundant at sites with low algal abundance, there is the widespread notion that macroalgae out-compete and displace sponges to habitats less suitable for algal proliferation. In this study, based on 292 sampling quadrats, we collected a total of 87 demosponge species and examined the level at which sponge distribution pairs with a variety of alga-dominated and animal-dominated habitats occurring in three zones located across a marked in-bay/out-bay environmental gradient. We found significant differences in sponge biomass, richness and diversity between the 18 habitats considered in the three zones, with abundance, richness and diversity being significantly higher in caves, vertical surfaces and overhangs out of the bay than in the remaining habitats. The cluster analysis and the unconstrained ordination consistently reflected the in-bay/out-bay environmental gradient. These analyses also revealed that the taxonomic distribution of sponge abundance is independent of the algal occurrence in the habitat, being more related to between-zone differences than to between-habitat differences. This trend was corroborated when the role of depth, algal abundance and substratum inclination in explaining total sponge abundance and diversity was examined by canonical correspondence analysis, regression analysis and mean comparisons. These analyses pointed to substratum inclination, rather than to algal abundance, as the factor explaining most variation in distribution of sponge abundance. These results, when discussed in the context provided by the outcome of other studies concerned with the spatial distribution of the sessile benthos in rocky temperate communities, strongly suggest a need to re-examine the idea that spatial distribution of sublittoral sponges largely results from competition with macroalgae.

Abundance, size, and feeding success of larval shortnose suckers and Lost River suckers from different habitats of the littoral zone of Upper Klamath Lake

We examined near-shore habitat use by larval shortnose and Lost River suckers in the lower Williamson River and Upper Klamath Lake of south-central Oregon. Emergent macrophytes Scirpus, Sparganium and Polygonum supported significantly more, larger, and better-fed larvae than submergent macrophytes, woody vegetation, or open water. Abundance, size, and gut fullness were similar for sucker larvae collected from different emergent macropytes. During the larval period, there was no evidence of density dependant effects or habitat shifts. Ranked catch per unit effort data indicated potential predators also were more likely to use emergent macrophytes, but ordination indicated larvae and potential predators were differentially distributed along a vegetation structure-water depth gradient with larvae in shallow vegetated areas. Between-habitat differences appeared to be due to larval sucker selection for, or better survival in, emergent macrophytes, rather than differential access or exclusion from other habitats. The importance of emergent macrophytes appears to be related to increased foraging success and reduced predation. Because larvae in emergent macrophytes have a size and gut fullness advantage, the amount of emergent habitat could affect early survival. However, interannual differences in recruitment to the adult population may or may not be dependent on larval dynamics. Our results suggest larval sucker access to emergent macrophytes may be necessary, but perhaps not sufficient, for promoting good year class formation.

Impacts of naturally-occurring soil fungi on seeds of meadow plants

Although soil fungi may represent an ecologically important cause of mortality of buried seeds, few studies have provided direct evidence of the pathogenicity of fungi colonizing seeds in natural habitats. In response, we conducted a series of experiments to investigate the impacts of soil fungi from a range of habitats on seeds of meadow plants. We compared the survival of seeds of four grasses in five habitats, and isolated fungi from these seeds. We then tested the pathogenicity of selected isolates against two standard sets of plant species: the original four grasses and a broad range of old field species. We found that the soil community contained a large variety of seed-colonizing fungi. Some, but not all, examples of these fungi caused seed mortality; others may be harmless commensals. Some of these isolates negatively affected a broad range of plant species, but others had a more restricted host range; as a result, pathogenicity varied depending upon the particular plant-fungus combination. Few between-habitat differences in seed survival were detected. Our results demonstrate that fungal seed pathogens are common, ubiquitous, and potentially lethal, but that their effects depend on the particular combination of fungus and plant species considered.

Artificial nest predation in natural and perturbed habitats of the central Monte Desert, Argentina

Abstract We examined nest predation rates at artificial nests in two contrasting habitats (open woodland and shrubland) inside the Reserve of Nacunan, west-central Argentina and in open woodlands within the reserve and a nearby grazed area, to assess whether between-habitat differences in vegetative structure were associated with changes in nest predation levels. We also quantified diurnal and nocturnal predation rates to further characterize the predator assemblage of the reserve. Nest predation rates and the estimated daily mortality rates were quite high in both open woodland and shrubland and did not differ significantly between them. Nest predation rate and daily mortality rate of nests in open woodlands of the reserve were high but similar to the rates for nests in adjacent grazed open woodlands. Nearly all predation events occurred during daylight hours. This result was not an artifact of the use of quail eggs because the proportion of depredated nests during the night was similar when we used smal...

CHARACTERISTICS OF DIET OF PEROMYSCUS AZTECUS AND REITHRODONTOMYS FULVESCENS IN MONTANE WESTERN MEXICO

We tested whether differences in composition and nutrients of diet explained higher density of Peromyscus aztecus in mature cloud forest and higher density of Reithrodontomys fulvescens in disturbed cloud forest. P. aztecus ate dicot leaves, stems, fruit, and seeds in mature cloud forest and dicot leaves, stems, and seeds, and monocot seeds and insects during the dry-hot season in disturbed cloud forest. R. fulvescens ate dicot leaves, stems, fruit, and seeds in mature cloud forest but monocots and insects during the hot season; dicot leaves, stems, and seeds were eaten in disturbed cloud forest. The diet of P. aztecus contained more protein and soluble carbohydrates in disturbed cloud forest where rodent density was lower; the diet of R. fulvescens contained more protein, lipid, soluble carbohydrate, Na, Mg, and P in mature cloud forest where density was lower. Nutrient differences resulted from R. fulvescens eating more monocots and dicot fruit, P. aztecus eating more monocot seeds and less dicot fruit, and both species eating more insects. Differences in composition or nutrient content of diet did not explain between-habitat differences in demography because nutrients in diet were higher in habitat of lower rodent abundance, suggesting other factors must be considered.

Clonal Growth and Ramet Performance in the Woodland Herb, Asarum Canadense

1 We report the results from a 7-year study on the patterns of reproduction and vegetative spread of Asarum canadense, conducted in replicate plots located in the understorey of early and late successional forest. 2 We recorded the spatial location, size, demographic performance and clonal fragment identity of all A. canadense ramets in our plots, as well as the position and fate of seedling recuits. We also collected detailed morphological data on patterns of clonal growth. 3 Recently germinated plants and the much larger, clonally produced daughter ramets had equal survivorship. Size also had little impact on rhizome production. Within sets of genetically identical ramets, flowering ramets were larger than non-flowering ramets. When there was an effect of habitat, ramets performed best in late successional forest. 4 Neither sexual nor asexual reproduction decreased the future performance of a ramet. Having connections to other ramets had little effect on survivorship or rhizome production, but often was associated with an increased probability of flowering. Clones with more ramets outperformed smaller clones and spread the risk of genet mortality. 5 Rhizome lengths were shorter in the high light, early successional forest, but no other clonal growth parameters differed between habitats. Empirically calibrated simulation and diffusion models indicated that the between-habitat differences in rhizome length were not great enough to affect the long-term expansion of clones. 6 Diffusion coefficients for the long-term spread by clonal growth or seed dispersal were compared for a number of species. Diffusion model results indicated that plants can disperse as far by clonal growth as they do by seed, although the values for A. canadense were 14 and 8895 cm2 year -1, respectively. 7 Asarum canadense appears to be under unusually strong selection for seedling survival. As has been observed for some other clonal plant species, few costs were found for either sexual or asexual reproduction.

Between-habitat differences in burrow characteristics and trophic modes in the southwestern Atlantic burrowing crab Chasmagnathus granulata

Burrow characteristics, food type, and feeding h a b ~ t s of the SW Atlantlc burrowing crab Chasmagnathus grdnulata were compared between ~ n d i v ~ d u a l s iving in mud flats and In Spartinadominated marshes. Burrows were shorter (X 19.7 cm, SD = 5 8, n = 54) and more dynamlc (entrance displacement: X = 3 2 cm d-l, SD = 1 7, n = 21) in mud flats than In Spartlna-dominated areas (length X = 41 cm, SD = 12, n = 78, no entrance displacement). Sediment turnover rate was much higher in mud flats (X 5 9 kg m-' d-l) than in Spartlna-dominated areas ( X = 2 4 kg m-' d.'). Burrow shape differed between areas, being straight, near-vert~cal tunnels in the vegetated area , but oblique (average angle to vertical = 60'. SD = 16, n = 110), and having a funnel-shape entrance and a much large]diameter in mud flats Stomach contents also differed between habitats. Pleces of plants dominated contents in the vegetated area , while sediment (with polychaetes, diatoms, ostracods, and nematodes) dom~na ted in the mud flats, lndicatlng that crabs are mainly deposit feeders In the mud flats and herb~vorous in the Spart~na-dominated areas. This pattern suggests that the heuristic model relatlng burrow arch~tecture to trophic modes prev~ously proposed for fossorial thalassinidean shrimps applies to individuals of a C granulata populat~on The burrow content showed higher organic content and vegetal parts in the vegetated area than in the other area. Burrows in the mud flat showed a significantly higher abundance of nematodes and ostracods. Due to their hydrodynalnic characteristics and content, burrows in the mud flats may work as passive traps for sediment and organic matter. Given the extensive intertidal area inhabited by C granulata in SW Atlantic estuanes, and the locatlon of their burrows (between marshes and the open estuary), these burrows may work as traps for detritus, thus reduclng the export rate of organic matter from marshes.

Enterobacterial attachment and effacement genotype among prospectively acquired putative enteropathogenic [formula omitted] serogroups

The digestive and metabolic characteristics at the biochemical level underlying between-habitat dietary shift of the SW Atlantic euryhaline burrowing crab Neohelice granulata under natural conditions are unknown. We made studies on adult males of N. granulata from the open mudflat and the vegetated saltmarsh in a SW Atlantic costal lagoon (Mar Chiquita, 37°32′–37°45′S; 57°19′–57°26′W, Argentina). We determined and compared amylase, maltase, sucrase, proteolytic, lipase and alkaline phosphatases activities in the hepatopancreas; glycemia, and glycogen, free glucose, triglycerides and protein concentrations in hepatopancreas, chela muscle, and anterior and posterior gills. The results show that N. granulata exhibits characteristics and between-habitat differences at the biochemical level (i.e. high amylase and disaccharidase activities, differences in total proteolytic, lipase and levamisole-insensitive AP activities in the hepatopancreas, and in the concentrations of glycogen in the gills, triglycerides in the hepatopancreas and of protein in the chela muscle) which could represent adaptive digestive and metabolic strategies to face the differences in environmental conditions (i.e. food availability). The possible relationship between digestive and metabolic characteristics and feeding patterns, type of food available and environmental conditions in each habitat is discussed.

Patterns of resource allocation to somatic, defensive, and reproductive functions in the Mediterranean encrusting sponge Crambe crambe (Demospongiae, Poecilosclerida)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 124:159-170 (1995) - doi:10.3354/meps124159 Patterns of resource allocation to somatic, defensive, and reproductive functions in the Mediterranean encrusting sponge Crambe crambe (Demospongiae, Poecilosclerida) Uriz MJ, Turon X, Becerro MA, Galera J, Lozano J The pattern of resource allocation in the sponge Crambe crambe (Schmidt) (Demospongiae, Poecilosclerida) in 2 contrasting habitats and in specimens of 3 size classes was studied. The sponge biomass per unit area increased with sponge size in both illuminated and dark environments. An increase with size was also found in the illuminated habitat for the investment in organic matter per unit area. This parameter was almost constant among the 3 size classes from the shaded habitat, with values similar to those of the medium-sized specimens from the illuminated environment. The amount of silica per mm2 was higher in the dark site where it proved size-dependent, whereas it did not vary with size in the illuminated habitat. Investment in reproduction per unit area was higher in the illuminated wall and was positively correlated with size in both habitats. The amount of calcareous debris included by the sponge during its growth did not vary across size classes in either habitat. All variables related to sponge thickness showed significant differences between the 2 sites studied, while neither the size nor the interaction of habitat and size significantly influenced their values. The specimens were thicker in the illuminated habitat, both in their choanosome and ectosome layers. No variations with size or site were found for the canal system. There was a significant habitat effect on the amount of matrix, which was higher in the illuminated environment. Sponges produced more collagen in the shaded environment than in the illuminated site. This was particularly true for specimens larger than 1000 mm2 (medium and large size classes). As for the number of fibres, there was also significantly more fibre material in the sciaphilous sponges. A significant interaction was found between habitat and size effects on the number of cells per sponge section. The pattern of resource allocation to the different functions considered was similar in medium-sized specimens from the 2 contrasting habitats except for the number of cells and amount of collagen per sponge section. Small and large sponges, on the other hand, featured the highest between-habitat differences in resource allocation. Large sponges from the illuminated habitat invested relatively more energy in organic matter and less in mineral and collagen structures than their sciaphilous counterparts. Small photophilic sponges invested more in silica than small sciaphilous specimens. Investment in reproduction was notably higher in the whole size range of photophilic sponges than in the corresponding size classes from the dark site. Consequently, this species seems able to shift its resource allocation as a function of size and environmental conditions. We propose an interpretation in terms of a higher competitive pressure in the shaded environment that results in increased investment in defensive/supportive (mineral and organic) structures and a lower investment in somatic growth (organic matter) and reproductive output (larvae). Resource allocation . Reproductive investment . Silica . Organic matter . Collagen . Cells . Spongin . Sponges Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 124. Publication date: August 10, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Sexual Habitat Segregation by American Redstarts Wintering in Jamaica: Importance of Resource Seasonality

ABsnTRCr.-We tested the hypothesis that wintering populations of American Redstarts (Setophaga ruticilla) segregate into different habitats by sex in response to ecological conditions associated with an extensive dry season, which typically develops after migrants arrive in northern Neotropical sites. Sex-specific distribution and overwinter persistence of redstarts were quantified at a Jamaican mangrove-scrub ecotone. We also contrasted vegetation structure and food availability in winter territories of the two sexes and in both habitats within and between seasons. Male and female redstarts were significantly segregated by habitat, with males holding territories in mangroves and females predominantly in contiguous scrub habitat. However, we found no significant sex-based difference in overwinter persistence on territories. The average mangrove territory had a higher canopy and more-open understory, higher relative humidity, and greater insect biomass within a season for several insect orders important in redstart diets. Canopy (leaf) cover and abundances of several insect taxa remained more constant over the dry season in mangrove than in scrub habitat. We argue that these between-habitat differences, especially seasonal stability of vegetation features and food abundances in mangrove habitats, affect winter habitat quality for nonbreeding redstarts. Received 3 March 1993, accepted 31 May 1993.

Strong Preferences for Apparently Dangerous Habitats? A Consequence of Differential Escape from Predators

Predators may affect prey populations not only through the direct removal of individual prey (e.g., Taylor 1984), but also through their prey's anti-predator behavior (e.g., Abrams 1984, Sih 1987, Kotler and Brown 1988). Several recent studies (see Lima and Dill 1990) demonstrate that these behaviorally-mediated effects are particularly important in determining the spatial distribution of prey in the environment: animals avoid habitats with abundant predators and correspondingly high risk of attack. This is a reasonable result, and ruling-out between-habitat differences in food abundance, mating prospects, etc., it might appear entirely general. However, consider the fact that habitat choice may be influenced by the probability of escape as well as the probability of attack itself. Studies of habitat use under the risk of predation have focused almost exclusively on habitat-specific attack rates, predator abundance, etc. (see Lima and Dill 1990), whereas habitatspecific escape has rarely been considered (or essentially held constant between habitats). When considering both attack and escape simultaneously, the above avoidance of habitats with high risks of predatory attack may no longer hold in general. This paper explores some simple ideas on why animals may not only prefer apparently dangerous habitats, but also exhibit such strong preferences for them that a very high risk of attack may not drive them away. Consider a generic animal with a choice between two habitats, designated 1 and 2. Let ai and ej represent the probability of attack in habitat i, and probability of escape given attack in habitat i, respectively. The probability of being killed by a predator in habitat i (Pi) is thus Pi = ai(1-ei). For simplicity, assume that the habitats differ only in Pi values, thus habitat 1 will be chosen when Pi<P2, or ai(1-ej)<a2(1-e2), which rearranges to

The effect of habitat on the helminth parasites of an island population of the Polynesian rat (Rattus exulans)

Differences in helminth faunal composition, distribution and abundance were studied in three habitats on an island on which the Polynesian rat, Rattus exulans (Peale), is the only rodent present. The effects of season and of host age and sex were also included in the analysis. Habitat had a statistically significant effect on the prevalence and/or abundance of all seven parasites included in this study. Season influenced four species (Brachylaima apoplania, Capillaria sp., Heterakis spumosa and Mastophorus muris) but had little or no detectable effect on the remaining three (Capillaria hepatica, Hymenolepis diminuta and Syphacia muris). Of the two intrinsic variables, age but not sex was found to have an effect. A comparison of the effects of each variable on parasite prevalence confirmed that habitat was the most important of the four variables. In a prior study on the influence of habitat on host population dynamics on this island, between‐habitat differences were shown to include adult longevity, total population density and the seasonal availability and abundance of various food types. These factors, together with physical differences in the microhabitat and the parasite's life cycle, help to provide explanations for the observed results.

Classification of Fish Assemblages based on Echo Integration Surveys

Echo integration data typically collected during fish biomass surveys have additional utility in species recognition. Our analysis is based on a rockfish (family Scorpaenidae) hydroacoustic survey off the northwest coast of Vancouver Island, British Columbia, Canada. Survey data from 105 echogram sections were divided into two categories on the basis of ocean bottom habitat. One category corresponded to an area of bedrock outcrops and the other to the continental slope adjacent to the shelf break. Hydroacoustic characteristics of the bottom-oriented fish assemblages associated with these habitats could be described by time of day, mean volume density, dispersion, and mean off-bottom distance of the biomass. Nearest-neighbour analysis of these features classified assemblages into habitat categories with up to 97% success. Between-habitat differences in the assemblages were also evident from concurrent experimental fishing. Different rockfish species dominated the assemblages in the two areas. Our results suggest general methods for distinguishing among species groups in hydroacoustic survey data.

Variation in Seed Size of a Southwestern Riparian Tree, Arizona Walnut (Juglans major)

-In southwestern North America, seed and nut size of the riparian tree Arizona walnut (Juglans major) have high variance among years, as well as within and among sites. Annual variance is attributable to differences in spring rain, with large viable seeds produced only in years with above-average rain. In apparent contradiction, trees in drier habitats (i.e., riparian terraces) produce larger seeds on average than those on streambanks. In drought years on terraces, seed weight is lowest on large trees that produce many female flowers. Seed weight declines significantly with tree age and size in terrace habitats. Between-habitat differences may reflect evolutionary processes that have selected for larger but fewer seeds in drier habitats, while competition between seeds may be a proximate cause of variance in seed weight among years and within habitats.