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1.
Grazers have been shown to affect assemblages of species in many habitats. Here we studied the effects of the gastropod grazers,
Austrocochlea porcata and Bembicium auratum, on intertidal estuarine assemblages in a sheltered bay in New South Wales, Australia. We examined the effects of gastropods
on individual species and on the assemblage as a whole. The multivariate response was compared with data on succession in
these assemblages to estimate potential effects of grazers on succession. The experiment was repeated several times to determine
the generality of grazer effects in the light of possible variation in the timing or intensity of recruitment. There were
different responses of individual species to the presence of grazers. Grazers reduced the abundance of ephemeral algal species,
bryozoans, copepods, insect larvae and Balanus spp. barnacles. They had a positive effect on oysters and spirorbids and no effect on the barnacles Elminius covertus and Hexaminius spp. These effects were consistent through time. Multivariate analyses confirmed that grazers caused significant changes to
whole assemblages and that these effects were far-reaching and not only caused by changes to algal species. The removal of
grazers appeared to neither speed up nor slow down succession, but rather caused a completely different assemblage to develop.
Apparent important mechanisms affecting the composition of animal species when grazers were removed included accumulation
of sediments and detritus and pre-emption of space by algae.
Received: 13 May 1996 / Accepted: 1 September 1996 相似文献
2.
Non-native aquatic macrophytes have invaded different types of ecosystems all over the world. The exotic submersed macrophyte
Hydrilla verticillata recently invaded the Paraná basin, Brazil, being recorded by the first time in the natural habitats of this river in 2005.
We investigated the effects of this species on ostracod assemblages and compared the abundance, richness, and Shannon–Wiener
diversity of ostracod assemblages that colonize the invading species with those that colonize Egeria najas, a native submersed species with similar architecture and physical complexity. Fragments of these two species were left for
28 days in tanks to root and grow and then they were transferred to a floodplain lake where they remained in pairs (one plant
of each species; N = 7) during 30 days for colonization by ostracods. A detrented correspondence analysis was used to summarize ostracod assemblage
composition. Although there were no significant differences in ostracod abundance, richness and Shannon diversity when analyzed
separately, cumulative curves, which permit to eliminate effects of abundance on richness, indicated a significantly higher
number of ostracod species on H. verticillata. Assemblage composition was significantly different between both plant species, as shown by the first DCA axis. Our results
show that H. verticillata might provide favorable habitats for native ostracod assemblages. 相似文献
3.
The effect of dispersal on single-species nonautonomous dispersal models with delays 总被引:4,自引:0,他引:4
In this paper, single-species nonautonomous dispersal models with delays are considered. An interesting result on the effect
of dispersal for persistence and extinction is obtained. That is, if the species is persistent in a patch then it is also
persistent in all other patches; if the species is permanent in a patch then it is also permanent in all other patches; if
the species is extinct in a patch then it is also extinct in all other patches. Furthermore, some new sufficient conditions
for the permanence and extinction of the species in a patch are established. The existence of positive periodic solutions
is obtained in the periodic case by employing Teng and Chen's results on the existence of positive periodic solutions for
functional differential equations.
Received: 26 June 2000 / Revised version: 6 October 2000 / Published online: 10 April 2001 相似文献
4.
Based on the investigation data of monsoon evergreen broad-leaved forest at its different succession stages (primary, CP; 15 years of succession, CF; and 30 years of succession, CT) in Pu' er of Yunnan Province, this paper studied the species-area relationship of this forest at each succession stage. It was found that in the communities at each succession stage, the number of total species, trees, shrubs, and lianas had a significant correlation with sampling area, with the area explained over 94% of the total variation. The Z value of the total species (0.334) and trees (0.394) was the lowest at CT, whereas that of shrubs (0.437) and lianas (0.326) was the lowest at CF. No significant differences were observed in the intercepts of the species-area curve of total species, trees, shrubs, and lianas among different succession stages, but the coefficient of determination (R2) of the species-area curve of total species and lianas was the highest at CP. The richness of trees and shrubs at CF explained 99.9% of the variance of Z value, but the richness of total species, trees, shrubs, and lianas at CP and CT had no significant correlations with the Z value. 相似文献
5.
Subtidal fouling assemblages usually consist of short-lived organisms. Colonisation sequences on man-made structures may thus be greatly affected by the temporal and spatial variability of propagule supply. This study explores the influence of seasonality on succession in the macrofouling assemblage of a Patagonian harbour (Argentina, Southwest Atlantic). Replicated artificial substrata were suspended horizontally and sampled at quarterly intervals during 1?year. The influence of seasonality on 1-year-old assemblages was further analysed using additional sets of replicated panels submersed at different seasons and collected 1?year later. Upper surfaces were always dominated by ephemeral algae, while lower surfaces exhibited high coverage of filter-feeding invertebrates. Regardless of submersion length, species richness was significantly higher on lower than on upper surfaces. A significant interaction between orientation and submersion length was found for the Shannon diversity index, meaning that temporal changes in diversity depended on substratum orientation. On the lower surfaces, diversity reached a maximum after 9?months and then declined, mainly due to extensive dislodgment of two species of ascidians. On algal-dominated upper surfaces, differences in structure of annual assemblages were due to seasonal changes in the abundance of ephemeral algae. This study shows that constancy or variability of 1-year-old assemblages whose development began at different seasons depended greatly on the life history of the organisms that settled and managed to persist on both surfaces, which in turn depended on substratum orientation. 相似文献
6.
Resource competition and suppression of plants colonizing early successional old fields 总被引:3,自引:0,他引:3
Early colonizing annual plants are rapidly suppressed in secondary succession on fertile midwestern old fields, while later
colonizing perennials persist. Differences in competitive ability for above- and belowground resources may be partly responsible
for differences in species persistence during succession, as both light and nutrient availability may change rapidly. We found
that, although both above- and belowground competition suppress growth of colonizing plants, belowground competition was the
dominant factor in the suppression of the annual Ambrosia artemisiifolia in 2nd-year-old fields near the W.K. Kellogg Biological Station in southwestern Michigan. Despite an ability to persist in
later successional fields, seedling transplants of the perennial Achillea millefolium were also suppressed by above- and belowground competition, with belowground competition having the strongest effect. As
in many old fields, nitrogen availability is the primary factor limiting plant productivity. There was no clear difference
between the species in ability to compete for 15N from an enriched patch, although there was an indication of greater precision of foraging by Achillea. Life history differences between these species and consequent differences in the phenology of root growth relative to other
old-field plants are likely to play a large role in the persistence of Achillea in successional fields where Ambrosia is suppressed.
Received: 8 January 1998 / Accepted: 16 September 1998 相似文献
7.
We report results from a 2-year study on the succession pattern of macrofouling assemblages in the Taranto Sea, an important alien species hotspot in the Mediterranean Sea. Four sets of PVC panels were used as macrofouling collectors; each unit was installed at a different time (April 2013, July 2013, October 2013 and January 2014) and then surveyed quarterly for 1 year. The macrofouling community consisted of 93 sessile invertebrate species, of which 16 were NIS and five were cryptogenic. In both years non-indigenous species (NIS) recruitment occurred mainly in the quarter July/October in concert with the settlement of pioneer autochthonous species. This recruitment is independent of immersion time, occurring on both bare substrates and on previously colonized panels. This increase in NIS coverage is influenced by the development stage of the community, suggesting that NIS grow better without potential competitors. Two sets of NIS were distinguished. The first included abundant ascidians, serpulids, and bryozoans that are structuring components of early communities when favorable conditions exist (i.e. a lack of competitive autochthonous species). After settlement, these species are unable to develop in later-stage communities. The second set of NIS was composed of sabellid worms that settle in early and late communities but, unlike the other NIS, are able to persist and become dominant in late macrofouling communities independent of seasonal changes. 相似文献
8.
H. R. Spieth 《Population Ecology》2002,44(3):0273-0280
The large white butterfly, Pieris brassicae, has an unusually complex life-history in its southernmost range in Western Europe. This complexity results (1) from two
developmental rests, a short-day induced hibernation and a long-day induced estivation response, and (2) from the exceptionally
early appearance of the first adult generation in January/February and a subsequent winter diapause in some of their progeny.
It was found that in spring and autumn, different generations are faced with critical photophases which induce hibernation
or estivation, with the consequence that in five out of six generations per year, only some develop directly whereas the others
enter a dormancy phase. To assess the implications of this high number of optional responses on the generation succession,
the development time was studied at various photoperiods and temperatures. The results showed that a threshold response determines
the duration of estivation. With unchanged summer conditions (daylengths ≥15 h) estivation lasts on average 18–19 weeks, while
with autumn conditions (daylengths ≤14 h) it lasts only 7 weeks. A change of photophases from ≥15 h to ≤14 h terminates estivation
within about 3–5 weeks, slightly depending on the pupal exposure time in summer conditions. The duration of estivation is
not affected by temperature or by the photophases experienced by the caterpillars. The winter diapause lasts 18–19 weeks on
average with winter conditions (12°C/10.30 h light), but only 8–10 weeks with late spring conditions (21°C/15 h light). These
results were used to assess the effects on the population phenology, with the finding that despite the different developmental
pathways, a desynchronization of the generation succession is largely prevented. Estivation, hibernation, and direct development
at different seasons are well adjusted to a common phenological pattern of a continuously reproducing population. This pattern
of activity covers a cryptic dormant subpopulation, and could not have been deduced by field observations.
Received: October 3, 2001 / Accepted: October 3, 2002 相似文献
9.
The species-area relationship in the hoverfly (Diptera, Syrphidae) communities of forest fragments in southern France 总被引:1,自引:0,他引:1
Annie Ouin Jean-Pierre Sarthou Bernard Bouyjou Marc Deconchat Jean-Paul Lacombe Claude Monteil 《Ecography》2006,29(2):183-190
The effect of forest fragmentation was studied in hoverfly communities of 54 isolated forests (0.14–171 ha) in south west France. The positive relationship between species richness and wood patch area was investigated by testing the three hypotheses usually put forward to explain it: 1) the sampling effect hypothesis, 2) the patch heterogeneity hypothesis, 3) the hypothesis of equilibrium between distance from other patch (colonisation) and surface area of the patch (extinction). The syrphid species were divided into 3 ecological groups, based on larval biology as summarized in the "Syrph the Net" database: non forest species, facultative forest species and forest species. A total of 3317 adults belonging to 100 species, were captured in the 86 Malaise traps. Eight species were non forest (N=16), 65 facultative forest (N=2803) and 27 forest species (N=498).
Comparison of the slopes of the species-area curves for species richness and species density per forest patch showed a strong sampling effect in the species-area relationship. Wood patch heterogeneity increased with wood patch area and positively influenced hoverflies richness. Less isolated wood patches presented high richness of forest species and low richness of non forest species. Only forest species richness seemed to respond to the equilibrium between surface area and isolation. Depending on which hypothesis explained best the species-area relationship, management recommendations to mitigate fragmentation effects were formulated at various spatial scales and for different stakeholders. 相似文献
Comparison of the slopes of the species-area curves for species richness and species density per forest patch showed a strong sampling effect in the species-area relationship. Wood patch heterogeneity increased with wood patch area and positively influenced hoverflies richness. Less isolated wood patches presented high richness of forest species and low richness of non forest species. Only forest species richness seemed to respond to the equilibrium between surface area and isolation. Depending on which hypothesis explained best the species-area relationship, management recommendations to mitigate fragmentation effects were formulated at various spatial scales and for different stakeholders. 相似文献
10.
In this study, sun leaf carbon isotope composition (δ13C) of two co-occurring woody Mediterranean species (Quercus pubescens Willd., a deciduous oak, and Q. ilex L., an evergreen one) was investigated on four sites with different water availability. The total range of δ13C values was 4.4 and 3.1‰ for Q. pubescens and Q. ilex respectively. The intra-site variability was about 3‰. Total mean per species was equal. There were significant differences
among sites, but at each site means of δ13C were not significantly different between species. A simple physiological model predicts no difference in intrinsic water-use
efficiency (WUEi) between evergreen and deciduous oaks. The relationship between site means of δ13C and water parameters suggests that there is a leaf functional adjustment with respect to available water resource. No correlation
was found between δ13C and the contents of any mass-based biochemical constituent. Nevertheless there was a significant correlation between δ13C and leaf mass per area of Q. ilex. For both species, there is also a positive correlation between leaf δ13C and individual crown area, i.e. a structural characteristic at tree level. Causal relations between δ13C and plant-environment interactions are discussed.
Received: 25 October 1996 / Accepted: 19 January 1997 相似文献
11.
We examined vertical migration and colonisation patterns of stream macroinvertebrates within the substratum of an Apennine
creek in NW Italy. Macrobenthos was sampled at three depths in the streambed (0–5, 5–10, 10–15 cm) by means of artificial
baskets filled with natural substratum. We placed 42 traps (5×5×15 cm), i.e. 21 top-opened (T-traps) and 21 bottom-opened
(B-traps), each composed of three overlapping baskets (high-H, medium-M and low-L), to evaluate differences in the vertical
movements. We also collected Surber samples to compare interstitial assemblages with streambed communities. The multilevel
traps yielded 42 taxa, compared with 60 taxa in the natural riverbed. Interstitial traps were rapidly colonised; both taxa
richness and organism number increased during the 42-day study period. We found active migration in both vertical directions,
but there were more invertebrates in the top-opened traps than in the bottom-opened traps. In the T-traps the most colonised
baskets were those placed at the H level, while in the B-traps the L level baskets were more rapidly colonised. The interstitial
assemblages differed markedly from the streambed communities in both composition and functional organisation, with more collector-gatherers
and predators in the interstitial zone and more filterers and scrapers in the natural riverbed. In Apennine lotic systems,
the interstitial zone is an important habitat for stream macrobenthos, although it may not be used by all species. 相似文献
12.
Concentrations of plankton, suspended particles 0.74–87 μm equivalent spherical diameter and dissolved organic carbon (DOC)
were measured from May to February at an Antarctic coastal site. Bacteria-sized particles 0.74–1 μm diameter, and bacterial
cells and heterotrophic protists all exhibited a seasonal minimum during winter and maxima in summer. Bacteria composed <10%
of the bacteria-sized particles. Release of autotrophic protists from the ice caused water column biomass of autotrophs to
reach maximum concentrations in October and November, but maximum cell concentration in the water column was reached in January.
Microheterotroph biomass weakly reflected the release of the ice algal community but reached maximum concentration during
the water column bloom in January. Total DOC concentrations varied from 0.36 mg C l−1 in July to 3.10 mg C l−1 in October, with a yearly average of 1.51 mg C l−1. Ultrafiltration of DOC revealed that the molecular weight composition of the DOC differed greatly through the year. DOC
<5 kDa molecular weight reached a maximum of 1.25 mg C l−1 in October and accounted for up to 60% of total DOC in July. Concentrations of high molecular weight DOC (>100 kDa) were
highest in July and November, with the DOC (100 kDa–0.5 μm) fraction reaching a maximum of 1.22 mg C l−1 in November and composing 82% of the total DOC in January. Wet chemical oxidation and high-temperature catalytic oxidation
organic carbon analyses were compared. Good correlation was observed between methods during summer but no significant correlation
existed in winter, indicating that winter DOC may be refractory.
Accepted: 21 March 2000 相似文献
13.
M. C. M. Cremen M. R. Martinez-Goss V. L. CorreJr. R. V. Azanza 《Journal of applied phycology》2007,19(6):615-624
Phytoplankton community composition, density, and succession were studied in tropical commercial ponds with euryhaline tiger
shrimp (Penaeus monodon Fabricius) using green-water technology at two different stocking densities [T1 10 post-larvae (PL) m−2 and T2 15 PL m−2] in one grow-out season (May–October 2005) in Leganes, Iloilo, Philippines. Weekly qualitative and quantitative analyses
of phytoplankton were done along with physicochemical analyses of the pond waters. A total of 103 taxa belonging to nine different
algal classes were observed. Of these classes, the Chlorophyceae, Cyanophyceae and Bacillariophyceae constituted the great
bulk of the phytoplankton population. The two treatments did not show any significant differences in the growth pattern of
phytoplankton over time and in their diversity indices. Although T2 had higher values than T1 for algal density and species diversity index, the differences were not significant. The mean Shannon-Wiener diversity index
for T2 (1.56) was higher than T1 (1.39) but not significantly different. Both treatment ponds had Chlorophyceae as the dominant algae during the initial culture
phase [0–35 days of culture (DOC)], which coincided with high salinity (average = 35.67 ppt) and relatively high N:P ratios
(average = 1.95). The chlorophycean bloom was made up mostly of Nannochloropsis sp. The cyanophycean bloom occurred towards the final culture phase (84–112/126 DOC) when there was low salinity (average = 19.5
ppt) and relatively high N:P ratios (average 2.01). A short diatom bloom occurred in T2 at the same time that the N:P ratios rose dramatically to 4.2 at 42 DOC. Among the eight physicochemical parameters examined,
positive correlations were noted among alkalinity, ammonium-nitrogen, nitrite-nitrogen and phytoplankton community. High species
diversity index and species richness could have enhanced the stability of favorable Nannochloropsis blooms, especially in T2. No differences were noted between the two treatments in terms of the shrimp’s biomass at harvest time (T1 = 28.9 and T2 = 29.4 g fresh wt per shrimp), although a significantly higher survival rate (P < 0.05) was observed in T1 (97%) than in T2 (56%). Both treatments were able to control the occurrence of the luminous bacterium Vibrio harveyi.
Presented at the 6th Meeting of the Asia Pacific Society of Applied Phycology, Manila, Philippines. 相似文献
14.
Stephen F. Matter 《Oecologia》1997,110(4):533-538
The relationship between population density and the size of host plant patches was investigated for the red milkweed beetle
Tetraopestetraophthalmus inhabiting unmanipulated patches of Asclepias syriaca. The resource concentration hypothesis proposes that density-area patterns, specifically that of increasing herbivore density
with patch size, are primarily a function of movement between host plant patches. This research investigated the degree to
which movement accounted for density-area patterns. Poisson regression analysis of beetle abundance versus milkweed patch
size revealed that beetle density tended to increase with patch size. The pattern of density and patch size resulted from
local reproduction and residence time. The density of emerging beetles tended to increase with patch size while emigration
rates were unrelated to patch size. Immigration rates were constant with patch size for male beetles, and decreased with patch
size for female beetles. Net flux of beetles (immigration – emigration) did not vary with patch size for male beetles and
decreased with patch size for female beetles. Comparisons are made between this system and previously studied systems where
movement plays a significant role in forming density area patterns. Additionally, several hypotheses are presented which may
account for greater in situ recruitment and residence time in large patches.
Received: 23 February 1996 / Accepted: 8 January 1997 相似文献
15.
Hermanni Kaartokallio Jaana Tuomainen Harri Kuosa Jorma Kuparinen Pertti J. Martikainen Kristina Servomaa 《Polar Biology》2008,31(7):783-793
Coastal fast ice and underlying water of the northern Baltic Sea were sampled throughout the entire ice winter from January
to late March in 2002 to study the succession of bacterial biomass, secondary production and community structure. Temperature
gradient gel electrophoresis (TGGE) and sequencing of TGGE fragments were applied in the community structure analysis. Chlorophyll-a and composition of autotrophic and heterotrophic assemblages were also examined. Overall succession of ice organism assemblages
consisted of a low-productive stage, the main algal bloom, and a heterotrophic post-bloom situation, as typical for the study
area. The most important groups of organisms in ice in terms of biomass were dinoflagellates, plasticidic flagellates, rotifers
and ciliates. Ice bacteria showed a specific succession not directly dependent on the overall succession events of ice organisms.
Sequenced 16S rDNA fragments were mainly affiliated to α-, β-, and γ-proteobacterial phyla and Cytophaga–Flavobacterium–Bacteroides-group, and related to sequences from cold environments, also from the Baltic Sea. Temporal clustering of the TGGE fingerprints
was stronger than spatial, although lower ice and underlying water communities always clustered together, pointing to the
importance of ice maturity and ice–water interactions in shaping the bacterial communities. 相似文献
16.
Longitudinal succession of stream fish faunas is commonly related to increasing stream size and stability. However, effects
of succession on assemblage morphology are seldom quantified. We used an ecomorphological approach to determine differences
in faunal structure among distinct stream types of the Cheyenne River drainage in South Dakota, USA. During May–October 2004
we collected fishes monthly from five streams. We examined 28 morphological traits of the dominant fish species and compared
morphological structure among faunas using univariate analysis of variance (ANOVA) tests and multivariate ordination and distance
calculation techniques. Species richness and composition varied between smaller creeks and larger rivers. Morphological diversity
increased with richness, but richer assemblages were also more tightly packed in morphospace, partly because of increased
cyprinid richness. Some morphological differences were predicted by variation in mean discharge and discharge flashiness (flow
stability). Fishes of more stable or larger river stations characteristically had smaller heads and mouths and longer intestines.
Larger mean standard length was also associated with less flashy flow regimes and higher mean discharge. All assemblages were
hyperdispersed in morphological space, consistent with the harsh zoogeographical history of the region and suggesting the
presence of open niches. Increasing species and morphological diversity despite increasing discharge flashiness suggests higher
niche diversity in Great Plains rivers compared to adjacent creeks.
Handling editor: J. A. Cambray 相似文献
17.
C. Suresh A. K. Dubey S. Srikanta S. Umesh Kumar N. G. Karanth 《Applied microbiology and biotechnology》1999,51(5):673-675
A UV-induced mutant strain of Aspergillus niger (CFTRI-1105-U9) overproduced a starch-hydrolysing enzyme with properties characteristically different from the known amylases
of the fungus. The purified enzyme of 4.0 pI had an apparent molecular mass of 125 kDa and it dextrinised starch and then
saccharified the dextrins. Patterns of the enzyme activity on starch, resulting in glucose at 60 °C and glucose, maltose and
maltodextrins at 70 °C as primary products, suggested significant applications for the enzyme in starch-processing industries.
Received: 29 October 1998 / Received revision: 11 January 1999 / Accepted: 19 January 1999 相似文献
18.
Two coals of different rank, mined in Russia, were treated by an anaerobic methanogenic enrichment culture. The addition
of alkaline enclosing rock to the lower-rank coal increased the pH of the incubation medium and methane production above that
of the higher-rank coal with addition of its enclosing rock. This effect was accompanied by the leaching of cations from the
incubation medium. The coal was processed without a preliminary chemical treatment in a two-stage aerobic/anaerobic bioreactor
containing an anaerobic methanogenic granulated enrichment culture.
Received: 15 January 1998 / Received revision: 2 October 1998 / Accepted: 2 October 1998 相似文献
19.
During January 1989, phytoplankton biomass and species composition were studied in a north / south transect at the Weddell / Scotia
Confluence (47°W), between 57° and 61°30′S. Results showed a diatom bloom in the Scotia Sea (chlorophyll a 1.9 μg l−1, particulate organic carbon 239 μg l−1), dominated by Fragilariopsis cylindrus, Dactyliosolen antarcticus and Chaetoceros dichaeta. Low chlorophyll a / phaeopigments ratios (about 1.4) and silicate concentrations (15 μmol l−1) suggested that this was an advanced bloom phase, probably linked to high grazing pressure. Minimum chlorophyll a values of 0.1–0.2 μg l−1 and particulate organic carbon 46 μg l−1 were found at the Weddell / Scotia Front and in a subsurface layer of the Weddell Sea Water. In the southern part of the
transect (61°30′S), in the Weddell Sea, a second surface maximum was found (chlorophyll a 0.9 μg l−1, particulate organic carbon 120 μg l−1), but with a different species composition, with Cryptomonas sp. dominant. Our results show a succession within the diatom community in the Weddell / Scotia Confluence Waters when comparing
the three EPOS legs. In the Weddell Sea from spring to summer, nanoflagellates, with only a minor contribution from diatoms,
persist over a long period with little change in the community structure. We suggest that the frontal system, together with
the receding ice edge and the grazing pressure of either krill or protozooplankton, are mainly responsible for the phytoplankton
distribution patterns found.
Received: 3 July 1996 / Accepted: 3 November 1996 相似文献
20.
Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position 总被引:4,自引:0,他引:4
Christopher M. Taylor 《Oecologia》1997,110(4):560-566
I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated
and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences
between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried
out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages,
and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected
pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types,
species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common
pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility.
To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following
two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration
should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly
nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were
significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important
in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three
species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool
volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position
within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization
potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and
land bridge islands, but at much smaller space and time scales.
Received: 6 December 1996 / Accepted: 10 December 1996 相似文献