Small-scale Distribution Patterns Research Articles

Small scale distribution patterns of female and male Daubenton's bats (Myotis daubentonii)

We analysed the distribution and relative abundance of Myotis daubentonii in the lowlands and uplands around the Lahn river near the city of Giessen (Hessen, Central Germany). We assumed a positive correlation between distribution and relative abundance of the trawling M. daubentonii with the amount of water surface in our study area. We further expected an unequal distribution of male and female M. daubentonii especially during the energy demanding pregnancy and lactation period of females. Daubenton's bats were found at 75% of the 64 ponds and lakes we surveyed by standardized nightly spotlight counts. The number of Daubenton's bats correlated positively with the area of the water surface and negatively with the distance to the nursery colonies. Nursery colonies were located with radio-tracking and existed predominantly in the lowlands close to the Lahn river. Mean flight distance between nursery colonies and foraging areas was 2.3 km (mean ± 1.4 km, range: 0.6–6.3 km). Sex ratio was determined at three sites studied in detail from 1992–2003 by mist-netting along regular used flight paths (n = 1,847 caught individuals). The number of female per male M. daubentonii was unequal and differed significantly between the three sites. In the lowland we found one site clearly dominated by females (median = 4.3 females per male, percentages of females 79.3%, n = 169 individuals) and a second site with an almost balanced sex ratio (median = 1.1 females per male, percentages of females 50.3%, n = 939 individuals). At the third site in the uplands males outnumbered females (median = 0.2 females per male, percentages of females 13.5%, n = 739 individuals). The percentages of females remained largely constant from spring to mid summer and changed at the beginning of September. The study revealed that a detailed knowledge of the spatial distribution of gender specific roost sites and key foraging habitats is necessary for the establishment of meaningful monitoring and conservation measures for bats.

Plankton biomass and larval fish abundance prior to and during the El Niño period of 1997–1998 along the central Pacific coast of México

The temporal and spatial distributions of zooplankton biomass and larval fish recorded during 27 months (December 1995–December 1998) off the Pacific coast of central México are analyzed. A total of 316 samples were obtained by surface (from 40–68 to 0 m) oblique hauls at 12 sampling sites using a Bongo net. Two well-defined periods were observed: a pre-ENSO period (December 1995–march 1997) and an ENSO event (July 1997–September 1998) characterized by impoverishment of the pelagic habitat. The highest biomass concentrations occurred at coastal stations during the pre-ENSO period. During the El Niño period no spatial patterns were found in coastal waters. The months with highest biomass were those in which the lowest sea surface temperature (SST) occurred (January–May), and this pattern was also observed during the ENSO period. A typical, although attenuated, seasonal environmental pattern with enhanced phytoplankton (diatoms and dinoflagellates) was prevalent during the El Niño event in nearshore waters. During the El Niño period the phytoplankton was mainly small diatoms (microphytoplankton), while dinoflagellates were practically absent. The most parsimonious generalized linear models explaining spatial and temporal distribution of larval fish species included the ENSO index (MEI), upwelling index (UI) and distance to the coast. The environmental variability defined on an interannual time-scale by the ENSO event and the seasonal hydroclimatic pattern defined by the UI (intra-annual-scale) controlled the ecosystem productivity patterns. The small-scale distribution patterns (defined by a cross-shore gradient) of plankton were related to the hydroclimatic seasonality and modulated by interannual anomalies.

Efficacy of passive integrated transponder tags to determine spawning-site visitations by a tropical fish

Individual identification of organisms is a crucial part of assessing the processes that influence small-scale distribution patterns and the maintenance of social organizations. This study evaluates the use of passive integrated transponder (PIT) tags to quantify small-scale space use in a marine damselfish, Pomacentrus amboinensis (Pomacentridae). Implanting small PIT tags in the body cavity of fish down to 5.2 g with a hypodermic needle had no adverse effect on mortality or growth over a 47-day tank study. A 63-day field study also showed that tags had no influence on body condition as measured by Fulton’s condition factor (K), gonadosomatic indices, or plasma cortisol levels (a physiological indicator of stress). The utility of PIT-tag technology is illustrated by preliminary information from a study on the diel periodicity of visitations to male nest sites by female P. amboinensis. Information suggests that there is a strong periodicity in visitations. Females first entered the nest site at 03:20 h, with 88% of the total of 4 h 45 min that females spent within a single nest occurring prior to dawn. Despite this, 81% of the total visitations to the nest occurred after dawn, with most being very brief, averaging 17 s. No one female monopolized access to the nest, with nine females accounting for 90% of the time that females spent within the nest site. This methodology will be particularly useful in the study of activity rhythms, patch dynamics, and social interactions in a wide range of marine organisms.

Spatial distribution of epigaeic predators in a small field in relation to season and surrounding crops

Abstract The arthropod predator community of an organically cultivated 0.3 ha field was sampled by pitfall trapping during 1 year and analysed for small-scale spatial distribution patterns and their seasonal variation. Due to the small size of the study site, most of the investigated species were able to colonise the whole field. Ordination analyses revealed significant differences in community composition (i) between field centre and margin in summer and (ii) between field parts adjacent to meadows or conventionally cultivated arable land in all seasons. Results changed considerably if only adult carabids or spiders were used instead of the whole predator community. During summer the following significant differences in community parameters were found: (i) total catches in the centre were nearly twice as high as near the margin, (ii) predator richness did not differ between centre and margin while significantly more species were found close to meadows and (iii) evenness and heterogeneity were significantly higher at the margin versus the centre. The arthropod predator community even of a small field site showed distinct spatial distribution patterns with seasonal changes. Selecting appropriate taxonomic groups is crucial for the outcome of such studies and should be tailored to the aim of the investigation.

Responses of seabirds, in particular prions (Pachyptila sp.), to small-scale processes in the Antarctic Polar Front

Small-scale distribution patterns of seabirds in the Antarctic Polar Front (APF) were investigated in relation to other biological, physical, and chemical features during the ANT-XIII/2 research cruise of R.V. Polarstern from December 1995 to January 1996. The APF is characterized by steep gradients in sea-surface temperature and salinity. Within the APF, gradient zones were closely associated with elevated levels of primary production, chlorophyll-a (chl-a) concentrations, and zooplankton densities. Even broad-billed prions (‘Pachyptila vittata-group’), which dominated the seabird community by 83% in carbon requirements, showed small-scale distributional patterns that were positively related to primary production, chl-a, and total zooplankton densities. The findings demonstrate a close, direct link between fine-scale physical processes in the APF and biological activity through several food web levels up to that of zooplankton-eating seabirds. Broad-billed prions appeared to forage on very small copepods (Oithona spp.) in close association with the front. Fish- and squid-eating predators showed poor correlations with small-scale spatial structures of the APF. However, in a wider band around the APF, most top predators did occur in elevated densities, showing gradual spatio-temporal diffusion of the impact of the APF on higher trophic levels.

Community structure of mesozooplankton in the Antarctic polar frontal zone in the vicinity of the Prince Edward Islands (Southern Ocean): small-scale distribution patterns in relation to physical parameters

Abstract Mesozooplankton community structure was investigated in four consecutive years from 1996 to 1999, during late austral summer (April/May), in the vicinity of the Prince Edward Islands. Sampling was carried out using a Bongo net with a mouth area of 0.25 m 2 , and fitted with 300 μm mesh. Surveys were of high resolution, with net tows being separated by ±10–20 km. Zooplankton species composition demonstrated a high degree of similarity between net tows, containing a mix of sub-Antarctic and Antarctic species. However, variation in species abundance levels showed that within each year of study the region was characterised by the presence of different zooplankton communities. These communities differed by as much as an order of magnitude in total zooplankton density. Analysis of physical variables indicated that zooplankton communities were associated with different water masses, identifiable by their physical characteristics. Sea temperature was the most important physical variable, accounting for as much as 69% of the variation in community structure. Communities were often not spatially discrete, and many stations demonstrated a high degree of similarity despite wide spatial separation. The heterogeneity in the biological and oceanographic environment extended to a small scale, on the order of 10 km. This is indicative of the oceanographic complexity of the region. The complex oceanography associated with shallow topography, including seamounts, islands, and frontal zones, indicates that small-scale spatial heterogeneity in zooplankton communities may be an important factor to consider when modelling these ecosystems.

The effect of natural variation in substrate architecture on the survival of juvenile bicolor damselfish

Coral reefs offer settling fish larvae a spatial mosaic of microhabitats that differ not only in structural complexity but also in the abundance and diversity of predators. This paper provides evidence that interactions between predators and prey are causally linked to variation in relevant architectural characteristics of natural substrates. Juvenile bicolor damselfish, Stegastes partitus, experienced greater mortality on Montastrea annularis boulder coral than on piles of Porites porites coral rubble. This pattern was consistent on both back and fore reef habitats. Architectural differences, variable encounter rates with predators, and access to different food sources all contributed to higher mortality. Spatial and structural differences among refuges provided by the two substrates were most important in affecting survival. Porites rubble contained almost three times the number of crevices (39.9 vs. 14.3 crevices m–2AM2), had a much smaller mean crevice size (15.9 vs. 48.5 cm2), and had a more complex internal structure than Montastrea coral. Survival of juvenile fish living on Montastrea coral was positively correlated with crevice density (r2 = 0.41) whereas survival of fish living on Porites rubble was negatively correlated with crevice size (r2 = 0.43). These patterns were evident on fore reef habitats only, whereas on back reef habitats no clear patterns emerged. The effect of these natural differences in architecture on mortality rates of juvenile S. partitus was experimentally tested in the field using a combination of natural and artificial substrates. As the number of large shelters was increased I found that the density of potential predators increased but the survival rates of juvenile bicolor damselfish declined. These results highlight the importance of structural architecture among common reef substrates in affecting predator-prey relationships and in determining the survivorship and small-scale distribution patterns of juvenile reef fish.

Freshwater and saltwater flooding response for woody species common to barrier island swales

Flood sensitivity of five woody species common to barrier island swale habitats was quantified in a glasshouse study to examine potential mechanisms affecting observed small-scale distribution patterns. Differential response to short-term (30 d duration) freshwater and saltwater flooding occurred among the five species. OnlyBaccharis halimifolia was sensitive to freshwater flooding. At both low (2 and 5 g L−1) and mid-range (10 g L−1) salinity,Myrica cerifera, Pinus taeda, andB. halimifolia were more sensitive thanJuniperus virginiana orIva frutescens. At low salinity, stomatal conductance was significantly reduced forM. cerifera, P. taeda, andB. halimifolia, although recovery occurred and there was no mortality. At midrange salinity, all five species showed reduced stomatal conductance, but recovery differed. Mortality was highest forM. cerifera andB. halimifolia (60%), followed byP. taeda (40%),I. frutescens (25%), andJ. virginiana (20%). In contrast, 100% mortality occurred for all species in high salinity treatments of 20 and 30 g L−1. Interspecific differences in response to flooding may be a mechanism affecting small-scale distribution patterns of woody species in barrier island swales.

Small-scale distribution and salinity response of Juniperus virginiana on an Atlantic Coast barrier island

A field and laboratory study examined the hypothesis that the small-scale distribution pattern of Juniperus virginiana on barrier islands is related to salinity patterns and plant responses to salinity. Temporal (May – October) and spatial variability in ground water availability, ground water salinity, and total soil chlorides were quantified across a Virginia barrier island. Groundwater depth and salinity increased throughout the summer; microtopographic position and location on the island also affected soil salinities. Highest salinities occurred near the ocean side beach and bay side marsh, as well as in low lying swales that flood during extreme high tides or storms. Median rooting zone chloride level for J. virginiana was 54 μg/g. In contrast, laboratory germination and growth studies indicated that J. virginiana was significantly affected only at high salinity levels (1000 and 1400 μg/g), suggesting that salinity is not the only factor regulating small-scale distribution patterns. The broad tolerance to salinity may account for the abundance of J. virginiana in coastal environments. Key words: barrier island, eastern red cedar, Juniperus virginiana, salinity response, water relations.

Salinity and the small-scale distribution of three barrier island shrubs

The importance of salinity to small-scale distribution patterns was examined for three shrubs common on barrier islands of the southeastern United States. Field measurements focused on the salt marsh – upland interface zone on Hog Island, Virginia, where Myrica cerifera, Baccharis halimifolia, and Iva frutescens form distinct distributional zones. Although considerable variation in salinity occurred throughout the growth season (June through October), total soil chlorides and groundwater salinity were lowest for M. cerifera, intermediate for B. halimifolia, and highest for I. frutescens. All three species showed similar diurnal and seasonal patterns in stomatal conductance and leaf xylem pressure potential, despite the differences in salinity. However, a laboratory experiment revealed interspecific differences in water relations when the three shrubs were exposed to identical salinity regimes. The field data and water relations experiment indicated M. cerifera is least tolerant to salinity, I. frutescens is most tolerant, and B. halimifolia is intermediate. Seed germination experiments revealed a similar response, except that B. halimifolia was more sensitive to salinity than M. cerifera. The interspecific differences in soil and groundwater salinity, along with the physiological response differences, indicated that salinity may be one of the major environmental factors influencing zonation among the three shrubs; however, the absence of I. frutescens and B. halimifolia in low salinity areas implied that other factors also influence zonation patterns on barrier islands. Key words: Baccharis halimifolia, Iva frutescens, Myrica cerifera, barrier island, salinity tolerance, shrub.

Larval supply of shorefishes to nursery habitats around Lee Stocking Island, Bahamas. I. Small-scale distribution patterns

Plankton nets moored in tidal channels around Lee Stocking Island, Bahamas, were used to monitor larval supply from Exuma Sound to benthic habitats on Great Bahama Bank in the winter months (December–February) of 1990–1991 and 1991–1992. A total of 10376 fishes were collected in 1990–1991 from 58 taxa; in 1991–1992, 13358 fishes were collected from 56 taxa. Vertical distributions of 16 dominant taxa suggested that most settlement-stage fishes were concentrated in surface waters Six taxa showed no yearxdepth interaction; of Fese, five were sigmficantly more abundant in the surface nets. Eight of the ten taxa with significant yearxdepth interactions displayed a tendency to be more abundant in surface layers than in sub-surface collections during the first year, but were more evenly distributed across surface and sub-surface collections in the second year of sampling. Larval supply of six taxa showed significant coherency over spatial scales from 0.5 to 1.5 km. Over scales up to 5 km, however, larval supply became largely decoupled at the daily level. Significant inter-annual variability in the vertical and horizontal distributions of settlement-stage fishes suggests that behavior may play a major role in determining larval supply in tropical shorefishes.

Importance of Intermittent Shade to the Ecophysiology of Subalpine Herbs

We report here on the importance of intermittent shade periods for improving water relations and, thus, daily carbon gain in two subalpine understorey herbs. Data on carbon assimilation and plant water status during intermittent sun/shade periods and continuous full sun periods are presented for Arnica latifolia and its congener, Arnica cordifolia. The apparent importance of natural shade periods to the physiological performance and differences in small-scale distribution patterns between the two congeners is discussed

Salt-Marsh Benthic Invertebrates: Small-Scale Patterns of Distribution and Abundance

Monitoring of small-scale distribution patterns of benthic invertebrates has demonstrated distinct trends in faunal abundances with position relative to individual culms of saltmarsh cordgrass,Spartina alterniflora, at Tar Landing Bay Marsh, near Morehead City, North Carolina. Samples containing culms ofSpartina yielded significantly higher abundances (at least three times) than did samples without them. Among common species, onlyNereis succinea did not show this effect. Matrix-arranged and randomly placed sets of samples have confirmed a positive relationship between cross-sectional area of culms in a sample (at the sediment-water interface) and contained numbers of macrofauna, juvenile macrofauna and meiofauna. These patterns occurred despite a decreased volume of sediment in samples containing culms. Heightened abundances of benthic invertebrates associated with structural elements at the sediment-water interface may result from either nonrandom recruitment (either active via recruit selectivity or passive through hydrogeographic effects of culms) or differential post-recruitment mortality (resulting from inhibition of epibenthic predators or from variable habitat quality).

Small-scale gold distribution patterns in the Precambrian Kimberley Reef placer: A case-study at marievale GMC., East Rand Goldfield, South Africa

The Kimberley Reef is a Proterozoic gold-uranium-placer which was deposited during the Kimberley stage of the Upper Witwatersrand System, approximately 2.7 × 109 years ago. The investigated site at Marievale GMC. is located towards the fanbase of the East Rand Goldfield. Geological, sedimentological, and geochemical parameters show that the placer formed in a fluviatil depositional environment (ca. 40 cm water depth) with a small-scale meandering stream pattern. Gold anomalies are elongated and frequently arcuate-shaped with sinuosities of ±1.5; their orientation reveals a high degree of variability on the scale of a few metres to tens of metres. They formed at the inside of meandering channel curves next to and alongside elongated conglomerate bodies which correspond to point bars. Concentrations of other heavy minerals formed according to their decreasing specific gravity at the outer, convex side and the downstream part of gold anomalies roughly in the order uraninite — pyrite and chromite — zircon. This sedimentary-controlled gold and heavy mineral distribution pattern was complicated by lateral channel migrations and frequent bed changes of streams, as well as subsequent faulting which had a depletioning effect on gold.

Spatial Pattern and Gamete Dispersal Distances in Atrichum angustatum, a Dioicous Moss

Spatial Pattern and Gamete Dispersal Distances in Atrichum angustatum, a Dioicous Moss

Pasture pattern on grazed slopes

Abstract The small-scale distribution patterns of pasture species were investigated on 10 uniformly “tracked” grazed slopes. Variations in relative abundance of the majority of species at all sites were closely related to ground surface configuration.