Abstract: We outline the potentially important role of dispersal in linking diversity patterns at different spatial and temporal scales, and the resulting potential to link hypotheses explaining macroscale patterns of diversity. We do this by proposing a possible mechanism linking climate to diversity patterns: we argue that climate, via effects of continuity of habitat availability in space and time, mediates a dispersal-ecological specialization trade-off at the metacommunity level that leads to latitudinal trends in dispersal ability, ecological specialization, range sizes, speciation and species richness, ultimately driving the latitudinal diversity gradient. This trade-off constitutes a possible mechanism for the strong macroscale correlation between climate and species richness that is consistent with recent ideas about niche conservatism and gradient lengths, as well as other leading hypotheses. We present an overview of predictions derived from our ideas. Of these, some have already been tested and supported and others are still open to debate or need testing. Together they provide a unique set of predictions that allows falsification.
Abstract: Individuals in natural populations commonly vary in color, and such color variation can be important for sur-
vival under predation pressure. Potential prey may be more likely to survive when they are cryptic against their back-
grounds. Alternatively, individual coloration, regardless of background, may itself best predict predation events. Few
studies have simultaneously tested the importance of crypsis and predator color preferences in explaining predation events.
In this study we used objective measures of coloration to examine whether heliconia bugs, Leptoscelis tricolor Westwood,
1842 (Hemiptera: Coreidae), resembling their background were less likely to be eaten by avian predators (crypsis hypothe-
sis). Next, we evaluated whether insect color, irrespective of background, best explains predation events (color preference
hypothesis). We found the strongest evidence for the crypsis hypothesis; predators chose prey that differed most from their
background in color saturation. Some evidence was also found for the color preference hypothesis; predators avoided
brightly colored prey. These results suggest that crypsis can be effective in detouring predation. However, when potential
prey are detected, predator color preferences may best explain predation events.
Abstract: Current evidence suggests regular overland transport of different freshwater invertebrates by wind, mainly over short distances. Yet, very little is known about the mechanism and scale of this process or about differences in wind dispersal dynamics and capacities among taxa and propagule types. We investigated wind dispersal of freshwater invertebrates in a cluster of temporary rock pools (spatial scale: 9,000 m(2)) in South Africa. Dispersing propagules and propagule bank fragments (i.e. aggregates of sediments and propagules) were intercepted during 1 month using a combination of windsocks (1.5 m above ground level) and sticky traps (ground level). The potential movement of propagule bank fragments (i.e. aggregates of propagules and sediments) was also simulated by tracking inter-pool movements of differently sized artificial substrate fragments similar to dry propagule bank fragments. We detected differences in the composition of dispersing communities intercepted at different altitudes (ground level and at 1.5 m). Comparison of dispersal distance distributions also revealed significant differences among taxa. Overall, larger propagule types (e. g. adult ostracods and oribatid mites) dominantly travelled near ground level while small resting eggs and cryptobiotic life stages of copepods were most frequently collected at higher altitudes (1.5 m) and dispersed over the longest distances. Finally, not only dispersal of single propagules but also ground level transport of propagule bank fragments was shown to contribute to local dispersal dynamics in temporary aquatic habitats.
Abstract: Fairy shrimps (Anostraca) live in temporary waters. Dominant among their predators are aquatic insects, especially diving beetles (Dytiscidae). Mastication of the eggs of the fairy shrimp Branchipus schaefferi and their passage through the digestive tract of smaller beetles, like Ilybius fenestratus, has a positive effect on hatching afterwards. Dytiscidae could be important vectors for aerial dispersal of diaspores among ponds which are not directly connected to a stream channel. Such long-distance dispersal can be of critical importance for population survival and gene flow among communities living in temporary habitats.
Abstract: 1. Heat tolerance of dry cysts of the fairy shrimp Branchipus schaefferi and the brine shrimp, Artemia franciscana was studied using rapid (similar to 100 degrees C/min) and slow (similar to 4 degrees C/min) heating. 2. Rapid heating caused much greater death than did slow, and we consider the possible causes. 3. Although these primitive crustaceans are closely related, the major stress proteins of Artemia cysts (artemin and p26) were not detected in Branchipus cysts. 4. The Arrhenius activation energy (E-a) for thermal killing of Branchipus cysts was found to be 5-fold higher than that of Artemia cysts over the range of 110-130 degrees C. 5. These major differences in stress proteins and Ea are especially interesting because the thermal tolerance of both kinds of cysts is very similar. (c) 2007 Elsevier Ltd. All rights reserved.
Abstract: 1. Many invertebrates inhabiting insular aquatic habitats rely on external agents or vectors to disperse. Besides water connections and wind, waterfowl and amphibians are known to mediate passive dispersal of freshwater invertebrates. However, the possibility of dispersal by terrestrial mammals has been largely overlooked. 2. We investigated the potential of both external and internal zoochorous dispersal of aquatic invertebrates by the wild boar (Sus scrofa) in Mediterranean wetlands in the Camargue (France). As wild boar frequently visit wetlands for feeding and wallowing purposes, we hypothesized that they may be important passive dispersal vectors of aquatic invertebrates at a local scale. Dried mud was collected from selected 'rubbing trees' used by boars to dispose of parasites. Additionally, faecal pellets were collected from different locations in the wetland area. 3. Seventeen freshwater invertebrate taxa including rotifers, cladocerans, copepods and ostracods hatched from sediment obtained from 'rubbing trees', while invertebrates hatching from dried faeces (10 taxa) were mainly rotifers. Dispersing invertebrates were collected up to 318 m from a nearest potential dispersal source. Both abundance and richness of invertebrates significantly decreased with dispersal distance. 4. Our results demonstrate that large mammals such as wild boar can act as dispersal vectors of aquatic invertebrates at a local scale in the wetland area of the Camargue and suggest that external transport may be quantitatively more important than internal transport. As wallowing (mud bathing) is common in many terrestrial mammals, this mode of dispersal may be quite widespread.
Abstract: The extent and frequency of passive overland dispersal of freshwater invertebrates as well as the relative importance of different dispersal vectors is not well documented. Although anecdotal evidence subscribing the feasibility of individual vectors in various aquatic systems is abundant, dispersal rates have rarely been quantified for different vectors in one study system. Earlier studies also usually investigated dispersal potential rather than actual dispersal rates. In this study we have estimated passive dispersal rates of invertebrate propagules within a cluster of temporary rock pools via water, wind and amphibians in a direct way. Overflows after heavy rains mediated dispersal of a large number of propagules through eroded channels between pools, which were collected in overflow traps. Taking into account model based predictions of overflow frequency, this corresponds with average dispersal rates of 4088 propagules/channel yr(-1). Wind dispersal rates as measured by numbers of propagules collected on sticky traps mounted between pool basins were very high (average dispersal rate: 649 propagules m(-2) in one month) and were positively related to the proximity of source populations. Finally, invertebrate propagules were also isolated from the faeces of African clawed frogs Xenopus laevis caught from the pools (on average 368 propagules/frog). The combination of short distance wind and overflow dispersal rates likely explain the dominant species sorting and mass effect patterns observed in the metacommunity in a previous study. Amphibian mediated dispersal was much less important as the Xenopus laevis population was small and migrations very rare. Based on our own results and available literature we conclude that both vector and propagule properties determine local passive dispersal dynamics of freshwater invertebrates. Accurate knowledge on rates and vectors of dispersal in natural systems are a prerequisite to increase our understanding of the impact of dispersal on ecology (colonisation, community assembly, coexistence) and evolution (gene flow, local adaptation) in fragmented environments.
Abstract: Despite an upsurge of interest in spatial interactions between communities and in the impact of dispersal on ecological and evolutionary processes, dispersal patterns and dynamics in natural metacommunities remain poorly understood. Although passive aerial dispersal of freshwater invertebrates is generally accepted, the frequency and relative importance of wind as a vector is still subject of considerable debate. We assessed the importance of wind dispersal in an invertebrate metacommunity in a cluster of 36 temporary rock pools on an isolated mountaintop in South Africa. Wind dispersal was quantified every four days using nine windsocks (about 1.5 m above rock base), placed in the field during one month. Distance to the nearest pool varied from 2 up to 16 m. Wind direction and speed were monitored for the entire period. About 850 propagules (mostly resting eggs) of 17 taxa were captured. The presence of water in the pools (level of exposure of the dormant propagule bank) and the dominant wind direction were the key factors affecting the yield. Wind speed was much less important. Our results suggest that wind dispersal of propagules from temporary aquatic systems is more frequent than previously thought. This may stabilise the metacommunity by mediating gene flow among populations and facilitating rapid (re)colonisation of patches. On the other hand, wind erosion of the dormant propagule bank may lead to egg bank depletion and local extinction. The measured frequent wind dispersal most likely fuels strong species sorting processes ultimately shaping the structure of the local communities as observed in an earlier study. To elucidate the link between local dispersal rates and their contribution to long range dispersal is a major challenge for future research on aerial dispersal of aquatic invertebrates.
Abstract: We compared dispersal rates and patterns using both spatial genetic structure as well as direct measures of dispersal in Branchipodopsis wolfi, a freshwater anostracan inhabiting clusters of spatially fragmented and temporally unpredictable ephemeral rock pools in southeastern Botswana. For a total of 29 populations from three rock pool sites, the active population component was subjected to allozyme analysis for four loci and gene flow between populations was estimated. For a subset of the pools, we quantified the number of viable floating dormant eggs and larvae dispersing into overflow traps during flood events. Genetic and geographic distances were significantly correlated within each site. Gene flow estimates indicated from 0.6 to 227 migrants per generation. This relatively high effective dispersal rate corresponds with our direct observation of peak dispersal between pools during floods. Up to 784 viable dormant eggs and 301 larvae were trapped at one overflow during one single rainfall event. We determined that a distance of 50 m is already an effective barrier to gene flow for this species. There is ample effective genetic communication between different populations within each rock pool site, but this communication is limited by distance.
Abstract: Hatching of resting eggs of Streptocephalus torvicornis (Waga, 1942) and Branchipus schaefferi Fischer, 1834, two sympatric fairy shrimps, was tested using medium in which these two species and Chirocephalus diaphanus (Prevost, 1803) had been raised. The medium of adults inhibited the hatching of conspecific nauplii, even when diluted by 50% using distilled water. Streptocephalus torvicornis resting eggs hatch in the medium of C. diaphanus but not in the medium of B. schaefferi. Resting eggs of B. schaefferi hatched in low numbers in S. torvicornis medium, and in high numbers in that of C. diaphanus. There appears to be one or more substances associated with the presence of adults of conspecifics and sympatrics which exceed the influences of abiotic factors, such as light, pH, conductivity and osmotic pressure in fresh media. We propose that this substance(s) functions as a pheromone to inhibit further hatching once a population of adults is present.
Abstract: The somatic growth, longevity, and reproduction of two Moroccan anostracan populations from different climatic areas were studied under standardized laboratory conditions. Both populations were subjected to allozyme analyses covering four loci, and molecular analyses of the variable regions, the Internal Transcribed Spacers (ITS1 & ITS2) intervening the nuclear ribosomal genes (18S, 5.8S, 28S rDNA). The ecological characteristics of the life cycle of each population are presented, together with their genetic differences and phylogenetic relationships.
Abstract: Explaining the variance of local communities in a spatial-environmental matrix is one of the core interests of ecology today. Recent progress in metacommunity theory has made a substantial contribution to this field, however good empirical data in support of available theories are still relatively scarce. In this study we sampled a cluster of 36 temporary rock pools four times during one season to assess invertebrate metacommunity structure and dynamics and to search for steering processes and variables. Both Mantel tests and redundancy models indicate that local abiotic factors were dominant over spatial factors in explaining community structure and both were acting independently. Spatial variables were only important for passive dispersers and significantly explained 11% of variation in this community component. Pools connected by temporary overflows hosted more similar communities of passive dispersers than unconnected ones while community dissimilarity significantly increased with inter-pool distance. A negative curvilinear relation was discovered between taxon richness and isolation in passive dispersers, providing some support for existing theoretical models of Mouquet and Loreau. Of different metacommunity perspectives, a combination of species sorting and mass effects best explains the observed patterns. Additionally, priority effects and monopolization may buffer against the homogenising effects of dispersal and contribute to the distinctness of isolated communities. This is one of the first studies to present evidence for spatial patterns in aquatic communities on such a small spatial scale (a rock ledge of +/- 9000 m(2)). Bridging the gap between theory and observed patterns in natural systems is one of the main challenges for future metacommunity research. Small aquatic habitats such as pitcher plants and freshwater rock pools may well have an important role to play as model systems to study ecological processes in a natural spatially explicit environment.
Abstract: The cyst deposition behaviour of Streptocephahis torvicarnis is described as the first documented case of active cyst deposition in Anostraca. The functional morphology of the brood pouch of S. torvicornis is described and illustrated using both Light Microscopy and Scanning Electron Microscopy. The brood pouch is an elongated tube-like structure with a subterminal crescent-shaped opening. During cyst deposition, the females insert this structure into the sediment to a depth of almost 10 mm, and deposit the resting cysts, analogous to an insect ovipositor. The opening mechanism of the genital pore is explained by contraction of a branched longitudinal muscle. The adaptive value of laying cysts into the soil and possible dispersal strategies are discussed.
Abstract: Growth, longevity, and reproduction of Tanymastigites perrieri (Daday, 1910) have been studied under standardized laboratory conditions at six different temperature regimes: 10, 20, 25, 30, 35, and 40degreesC. The development D of the shrimps as a function of the temperature T is expressed as K = D(T - Q. The temperature at which development stopped is C = 4.32degreesC, while K is a thermal constant, the number of degrees-days above threshold, or the physiological time (K = 719 degrees-days). The highest growth rate occurred at 25degreesC. The greatest body size, however, was attained in animals reared at 10degreesC (22 mm). Longevity decreased with increasing temperatures (from 41 days to 4 days). Maturation time was inversely related to temperature (from 20 days to 4 days; at 40degreesC no larvae survived). Offspring per individual varies with temperature (maximum 447 eggs at 20degreesC); while the innate capacity for increase, r, fluctuates between 0.07 and 0.34.
Abstract: Branchipus schaefteri and Streptocephalus torvicornis commonly co-occur in ephemeral ponds throughout the Mediterranean Region. We compared survivorship, growth, and reproduction. Our results show statistically significant differences in all three parameters under laboratory conditions at 25degreesC, reflecting different life history strategies between these species. Branchipus schaefferi grows quickly to 18 mm body length, producing roughly 1700 cysts during an average lifespan of 24 days, while S. torvicornis lives an average of 120 days (length 24 mm), laying 2400 cysts. This suggests that S. torvicornis is better adapted to deep longer-lived pools, whereas B. schaefferi may survive in small, more ephemeral pools as formed from spring melt water and autumn rains. While the lifespan is equal for both sexes in B. schaefferi, the males of S. torvicornis live 2.8 times longer than females (325 days versus 114) compelled into a long postreproductive period by lack of females in their environment.
Abstract: This paper presents a SEM documentation of the larval development of the two most abundant Austrian conchostracan species, Imnadia yeyetta (Limnadiidae) and Leptestheria dahalacensis (Leptestheriidae). As in several previously examined spinicaudatan species, five larval stages were documented: Nauplius 1, Nauplius 2, Metanauplius, Peltatulus, and Heilophore. Additionally, three postlarval stages of L. dahalacensis and the first larval instars of Eoleptestheria ticinensis and Limnadia lenticularis are shown and compared with the examined stages. Species identification of conchostracan larval stages is possible by using surface structures, and using SEM methods, except for L. lenticularis which can be identified more easily on the characteristic shape of the labrum.
Abstract: For the first time, Anostraca, Notostraca and Conchostraca (Laevicaudata, Spinicaudata) will be listed in the Austrian Red Data Book of Endangered Species. According to the 1999 IUCN draft criteria, eight out of 15 large branchiopod species recorded between 1994 and 1999 are considered as critically endangered, three of which (Chirocephalus shadini, Eoleptestheria ticinensis, Streptocephalus torvicornis) occur at only one site each. Five species are considered as endangered, two of them (Branchinecta orientalis, Triops cancriformis) showing a statistically significant decrease of sites. Eubranchipus grubii and Lepidurus apus, both found abundantly mainly in the flood plains along the rivers Thaya and Morava, are near threatened. Lynceus brachyurus is extinct in Austria. Large branchiopods are mainly threatened by agricultural activities and hydrological/hydrochemical changes. Presently, three Austrian locations are protected exclusively on the basis of large branchiopod occurrence; three additional habitats are in the process of obtaining official protection. Several large populations are situated in the WWF nature reserve "March-Auen", and in the National Parks "Donau-Auen" and "Neusiedler See - Seewinkel", respectively.
Abstract: Limnadia lenticularis, a well-known representative of the Conchostraca Spinicaudata in Europe, was generally accepted as a parthenogenetic species. During an intensive faunistic study of Austrian conchostracans, four of a total of 364 collected L. lenticularis specimens were males. This paper provides the collection localities, compares the sex ratios of the five conchostracan species found in Austria, and describes the general morphology of L. lenticularis males, focussing on SEM of the male claspers.
Abstract: Evidence is provided for the first time that at least part of the egg bank of the southern African fairy shrimp Branchipodopsis wolfi is dispersed over short distances by wind. A total of 423 sticky surfaces were mounted around and between individual basins at three rock pool sites, to trap any dispersing eggs during a 3 day period. Eight viable eggs were found in different egg traps (1.9% of the total), seven of which were located at one site with shallow basins. Given the proximity of vast egg basks to the egg traps, the low observed dispersal rate cautions against overestimating the importance of wind dispersal for population genetic processes. By generating egg banks to hedge against drought catastrophes, and producing egg types with different potential dispersibility, B. wolfi is a strong bet-hedger which has established a means of escaping temporal and spatial stress. These life history functions enable populations to persist in small desert rock-pools, which are the most extreme of temporary habitats. (C) 1999 The Linnean Society of London.
Abstract: Streptocephalus torvicornis and Branchipus schaefferi, males and females separately, were fed Escherichia coli at densities ranging from 1 x 10(6) to 5.5 x 10(7) ml(-1). These shrimps are able to consume large quantities of E. coli. Branchipus schaefferi consumed 4 x 10(8) E. coli ind(-1) hr(-1) and S. torvicornis consumed 5 x 10(8) E. coli ind(-1) hr(-1) (0.082 mg hr(-1) ind(-1)). Consumption leveled at an initial density of 4 x 10(7) E. coli ml(-1) for B. schaefferi, while for S. torvicornis consumption leveled at 4.5 x 10(7) E. coli ind(-1) hr(-1). The functional response curves of these filter-feeding shrimps showed an unexpected pattern. For the males of both species, at 15 x 10(6) E. coli ml(-1) there was a small decrease in consumption, while the curves of the females showed a similar decrease at 20 x 10(6) E. coli ml(-1). This phenomenon is explained by assuming that the distance between the setae of the limbs, the movement rate of the thoracic appendages, or the inclination of the filtering apparatus is altered. During 5-h experiments, both species do not feed at a constant rate.
Abstract: The transport rate of chalk, clay particles and algal cells (Scenedesmus sp.) through the digestive tract of Streptocephalus torvicornis and Branchipus schaefferi is described under experimental conditions. Differences in transport rate as well as in the degree of digestion at a fixed particle density of algae were found. In S. torvicornis, the transport rate is higher and the digestion of algae lower than in B. schaefferi. These differences might reflect trophic differences related to niche partitioning in these sympatric species.
Abstract: In Austria, the distribution of Anostraca, Notostraca, and Conchostraca is mainly confined to the flood plains of the rivers Morava and Danube, and the shallow alkaline pans of the Seewinkel region in Burgenland province. Occasionally, large branchiopods can also be found in rain pools of the eastern and central Austrian lowlands, where topography and climate favour the existence of astatic water bodies. Differences in hydrology, temperature and water chemistry requirements may be reflected in local species compositions and species seasonal appearance. A survey conducted from 1994 through 1996 found that Chirocephalus shadini, Eubranchipus grubii, and Lepidurus apus occurred in late winter and spring, while Branchinecta ferox, Branchinecta orientalis, Cyzicus tetracerus and Chirocephalus carnuntanus were found exclusively in spring. Streptocephalus torvicornis, Tanymastix stagnalis, and Eoleptestheria ticinensis were present in spring and summer. Branchipus schaefferi was found in summer and fall, whereas Imnadia yeyetta, Leptestheria dahalacensis, Limnadia lenticularis, and Triops cancriformis occurred throughout spring, summer and fall. Streprocephalus torvicornis was documented for Austria for the first time since 1965.
Abstract: According to recent literature, five of the six known Austrian 'conchostracan' species are extinct. However, interim results of a current study on large freshwater branchiopods in Austria show that five species still occur at a restricted number of sites in the Pannonian region of Lower Austria. The clam shrimps Leptestheria dahalacensis and Eoleptestheria ticinensis were rediscovered in May 1994 in the flood plains of the river Morava near Marchegg. Imnadia yeyetta and Cyzicus tetracerus have been known to the authors in the same region since 1981, and 1992, respectively. Limnadia lenticularis occurs in the flood plains of the rivers Morava and Danube. Lynceus brachyurus, the only Austrian representative of the Laevicaudata, was not found and most probably got extinct. All Austrian clam shrimp species are considered to be endangered. Main threats are agricultural activities and artificial changes of the hydrologic conditions. Conservational measures are discussed for their effectivity.
Abstract: Habitat preference, seasonal occurrence, starvation resistance, hatching of eggs of Branchipus schaefferi, and effects of predation on B. schaefferi were studied. Branchipus was only present in turbid, unvegetated ponds and absent in ponds which contain higher aquatic vegetation and the alga Spirogyra sp. The first individuals of B. schaefferi appeared in April when mean water temperature was approximate to 10 degrees C and the last adults in November at a water temperature of 3.5 degrees C. Up to 6 reproducing generations were observed during this period. Abundance of B. schaefferi was higher in temporary ponds than in permanent ponds. Sex ratio was close to unity for most of the year. Body size of B. schaefferi males and females was significantly positively correlated with pond volume. Without food B. schaefferi could survive for 1.5 to 2 days at 20 degrees C and 4 to 5 days at 10 degrees C. Hatching success of eggs decreased when eggs were dried for greater than or equal to 7 months. Freezing of eggs had no effect on hatching success. From the predators tested, Chaoborus sp. larvae clearly selected small B. schaefferi; one consumed approximately 6 Branchipus d(-1) at a density of 6 to 12 prey l(-1). The other predators, dragonfly larvae, and larvae and adults of Triturus alpestris selected alternative prey types, for example Tubifex sp. and ostracods.
