Climate change affects colonization dynamics in a metacommunity of three Daphnia species

Climate change is expected to alter the range and abundance of many species by influencing habitat qualities. For species living in fragmented populations, not only the quality of the present patches but also access to new habitat patches may be affected. Here, we show that colonization in a metacommunity can be directly influenced by weather changes, and that these observed weather changes are consistent with global climate change models. Using a long‐term dataset from a rock pool metacommunity of the three species Daphnia magna, Daphnia longispina and Daphnia pulex with 507 monitored habitat patches, we correlated a four‐fold increase in colonization rate with warmer, drier weather for the period from 1982 to 2006. The higher colonization rate after warm and dry summers led to an increase in metacommunity dynamics over time. A mechanistic explanation for the increased colonization rate is that the resting stages have a higher exposure to animal and wind dispersal in desiccated rock pools. Although colonization rates reacted in the same direction in all three species, there were significant species‐specific effects that resulted in an overall change in the metacommunity composition. Increased local instability and colonization dynamics may even lead to higher global stability of the metacommunity. Thus, whereas climate change has been reported to cause a unidirectional change in species range for many other species, it changes the dynamics and composition of an entire community in this metacommunity, with winners and losers difficult to predict.     

Size-selective dispersal of Daphnia resting eggs by backswimmers (Notonecta maculata)

Freshwater zooplankton is increasingly used to study effects of dispersal on community and metacommunity structure. Yet, it remains unclear how zooplankton disperses. Clearly, birds and wind play a significant role as zooplankton dispersal agents, but they may not always be the main vectors. This experimental study shows that a cosmopolitan aquatic insect, Notonecta, can be an important vector of cladoceran resting eggs (ephippia). Dispersing Notonecta frequently transported ephippia during flight, with a bias towards smaller ephippia in two species. A similar trend was present at the species level: Daphnia species with smaller ephippia were more often dispersed, suggesting that Notonecta could generate specific colonist communities. In addition, buoyancy appeared a critical trait, as non-floating ephippia of Daphnia magna were never dispersed. Our data suggest that Notonecta could be important dispersers of Daphnia, and that knowledge of dispersal dynamics of Notonecta may be used to predict Daphnia dispersal, colonization and resilience to disturbance.     

Abundance�Coccupancy relationships in metapopulations: examples of rock pool Daphnia

Intraspecific positive relationships between abundance and occupancy are observed for many species, suggesting that the same processes drive local and regional species dynamics. Two main groups of mechanisms explain this relationship: spatiotemporal variation in local population growth rates due to variation in habitat quality, or dispersal effects that increase occupancy of a species when locally abundant. Several studies show that spatiotemporal variation in population growth rates causes positive abundance?Coccupancy relationships, but few have shown dispersal effects. It is believed that such effects should be more evident for species whose dispersal is limited, e.g. metapopulations, but those studies are limited. This study investigates abundance?Coccupancy relationships in three Daphnia metapopulations in rock pools and the degree to which dispersal or habitat quality affect their local abundances and occurrence. Daphnia longispina and Daphnia magna showed positive abundance?Coccupancy relationships, but not Daphnia pulex. No single ecological factor could explain the abundance?Coccupancy relationships of any given species. Instead, dispersal processes and rock pool quality (mainly salinity and depth) seem to act together to shape the abundance?Coccupancy relationships. Such a conclusion is also supported by an immigration experiment in natural rock pools. This study suggests that although positive abundance?Coccupancy relationships may be commonly found for metapopulations, both dispersal processes and variation in habitat quality can be factors determining the abundance?Coccupancy relationship of metapopulations experiencing habitat heterogeneity.     

Assembly of zooplankton communities in newly created ponds

1. The creation or severe disturbance of habitat patches is generally followed by a phase of community (re)assembly. After such an event, the trajectory of community assembly in habitat patches may be highly variable because of stochasticity during the dispersal and colonization process. Conversely, assembly patterns may also be deterministic if communities are shaped by prevalent environmental conditions in the habitat patches (species sorting), or by systematic differences in the dispersal capacities of species. 2. In this study, we investigated the pattern of community assembly of zooplankton species in 25 newly created ponds at 13 different sites in Flanders (Belgium). Over a period of three consecutive years, we assessed at what rate and with what frequency species of the regional species pool colonized the newly created ponds. We also studied the development of community structure over time and tested whether the dynamics were consistent across different ponds at the different locations. In addition, we characterized the dynamics of metacommunity features, such as alpha, beta and gamma diversity in clusters of ponds. 3. Even within the first year after their creation, the new ponds were rapidly colonized by a small subset of species from the regional species pool (Daphnia obtusa, Chydorus sphaericus and Simocephalus vetulus). These species dominated the cladoceran assemblages during the subsequent years. Other species in the regional species pools were only sporadically able to colonize ponds. 4. During the entire study period, we observed no significant shifts in species lists or in the occurrences of species among years. The low incidence of the majority of species may be the result of dispersal limitation or the failure of immigrants to establish due to priority effects exerted by the first colonizers. There was, nevertheless, a consistent change in the relative abundance of species, which was most probably mediated by differences in the hatching time among species influencing species composition in the first year. 5. In contrast to expectations, we observed no increase in average alpha diversity (local species richness) and gamma diversity (total richness of entire pond clusters) during the course of the study period. Beta diversity was relatively low from the beginning and remained constant throughout the study period. These deterministic patterns can mainly be attributed to the dominance of the three first colonizing species and the low success rate of other species in colonizing the ponds.     

Colonization of Daphnia magna in a newly created pond: founder effects and secondary immigrants

In habitats recently colonized by cyclical parthenogens, founder events lead to genetic differences between populations that do not erode quickly despite ongoing dispersal. By comparing the genetic composition during initial colonization with that of the diapausing egg bank at a local scale, we here present the relative contribution of the founding clones to the build-up of genetic diversity and differentiation of a newly established cladoceran population. We monitored the population genetic structure of Daphnia magna in one newly created pond as well as the diapausing egg banks of four water bodies in the neighbouring area. Our population was founded by four individuals. After the first growing season, the largest contribution to the sexually produced resting egg bank came from only two clones. Descendants of initially rare clones and potentially also additional immigrant clones profited from outbreeding vigour and increased their frequency during the first few years after colonization. Beyond this, no further significant changes in genetic structure were observed in the egg bank. At this point, priority effects became fully operational and led to sustained population genetic differentiation from nearby ponds. Our results support that colonization dynamics strongly influence within and among population genetic variation and evolutionary potential of populations.     

The Cladocera of Sri Lanka (Ceylon), with remarks on some species

The freshwater Cladocera of Sri Lanka has been revised based on the study of over 700 zooplankton samples collected from all habitat types during 1965–1980. The cladoceran fauna is represented by six families; members of the families Polyphemidae, Leptodoridae and Holopedidae are absent. The common temperate genus Daphnia is rare.Sixty-two species have been recorded from Sri Lanka. Of these, five are new records. Remarks on a few species are given with illustrations. The distribution of Cladocera in different types of habitats is discussed. The greatest species diversity was found in ponds. The Sri Lankan fauna is numerically and in species diversity typical of tropical cladoceran fauna. It resembles the southern Indian fauna very closely except for the absence in Sri Lanka of the genera Acroperus and Camptocercus.     

Are they still viable? Physical conditions and abundance of <Emphasis Type="Italic">Daphnia pulicaria</Emphasis> resting eggs in sediment cores from lakes in the Tatra Mountains

All species of Daphnia (Cladocera) produce, at some stage in their life cycle, diapausing eggs, which can remain viable for decades or centuries forming a “seed bank” in lake sediments. Because of their often good preservation in lake sediment, they are useful in paleolimnology and microevolutionary studies. The focus of this study was the analysis of cladoceran resting eggs stored in the sediment in order to examine the ephippial eggs bank of Daphnia pulicaria Forbes in six mountain lakes in the High Tatra Mountains, the Western Carpathians (northern Slovakia and southern Poland). Firstly, we analyzed distribution, abundance and physical condition of resting eggs in the sediment for their later used in historical reconstruction of Daphnia populations by genetic methods. To assess changes in the genetic composition of the population through time, we used two microsatellite markers. Although DNA from resting eggs preserved in the High Tatra Mountain lake sediments was extracted by various protocols modified for small amounts of ancient DNA, DNA from eggs was not of sufficient quality for microsatellite analyses. Distribution curves of resting eggs from sediment cores correspond to the environmental changes that have occurred in the High Tatra Mountains area during last two centuries (atmospheric acid deposition, fish introduction) and demonstrate their influence on natural populations. Evaluation of ephippia physical condition (the most common category was empty ephippial covers) suggests that the majority of resting eggs hatched to produce a new generation of Daphnia or may be due to failed deposition of resting eggs by Daphnia to the chitinous case. In conclusion, age, low quantity and poor physical condition of resting eggs from these Tatra lake sediments proved to be unsuitable not just for use in genetic analyses, but also the possibilities of autogenous restoration of Daphnia populations from the resting egg banks in the Tatra sediments are negligible.     

Hatching of cladoceran resting eggs: temperature and photoperiod

Summary 1. We identified temperature and photoperiod conditions under which the hatching of 45 cladoceran species could be elicited. Identification of appropriate hatching cues is of primary importance for the exploration of the ties between active and diapausing stages.
2. Incubation temperature affected the hatching success of resting eggs isolated from Danish, Belgian/Dutch and Spanish sediments. In general, most hatchlings and species were retrieved at 15 °C. Danish and Belgian/Dutch resting eggs hatched more successfully under a long day photoperiod than in continuous illumination.
3. Most species could be retrieved after incubation of resting eggs isolated from a limited amount of sediment (0.4 kg) under a single, well chosen combination of temperature and photoperiod. Processing additional sediment samples under seven more incubation regimes only allowed detection of 21% (Spain) to 34% (Denmark) more species.
4. The incubation period for resting eggs to hatch was strongly influenced by incubation temperature. Our results show that hatching experiments aimed at assessing cladoceran species richness and conducted at 15 °C should be continued for a period of at least 2 weeks, after which a random subset of hatchlings (e.g. n  = 100) can be selected from the total hatchling assemblage.     

Influence of overwinteringDaphnia on spring zooplankton communities: An experimental study

To evaluate the influence of overwintering individuals of zooplankton on spring zooplankton communities, the dynamics of zooplankton communities with or without overwintering individuals were observed in experimental ponds from fall to spring. An insecticide, carbaryl, was used to regulate the overwintering individuals. In ponds which received insecticide applications in November or January, all cladoceran and rotiferan species were eliminated by the treatments and did not reappear until late March or early April, even when the chemical disappeared rapidly. The low water temperature may delayed the establishment of the populations from resting eggs. In these ponds, populations of various cladoceran and rotiferan species, which seemed to be originated from resting eggs, were built up in the spring. In control ponds,Daphnia ambigua orD. longispina overwintered as juveniles and adults and established a large spring population earlier than other cladocerans and rotifers overwintering as resting eggs. The latter zooplankters did not increase in the spring probably because their growth was suppressed by the precedingDaphnia species through competition. In nature, even if the number of overwintering individuals is small, they may have a potential to build up a large population earlier than the individuals hatching from resting eggs. As a result, the species which have overwintered as individuals seem to predominate in the spring and have a large influence on the spring zooplankton community.     

What can resting egg banks tell about cladoceran diversity in a shallow subtropical lake?

Dormant stages (“resting eggs”) produced by cladocerans can persist for long periods of time in sediments and restore populations once the environmental conditions become favorable again. Lake Blanca, a subtropical shallow eutrophic lake, hosts a cladoceran community dominated by small-sized species. Previous studies on zooplankton resting eggs suggested that the cladoceran genera Daphnia and Simocephalus were present, but they had never been found before in water samples. In the present study, we compared a biweekly active community sampling with the resting egg bank (passive cladoceran community) from littoral and pelagic zones. Moreover, we tested the amount of samples required to have a representative reconstruction of the diversity in both compartments (water and sediment). Lake Blanca showed a relatively high cladoceran species richness (24) in the water column, with rapid temporal replacement. Several species were present in water samples during short temporal windows; therefore, to detect these species a strong sampling effort in terms of temporal frequency and spatial distribution was required. Contrary to our expectations, resting egg community showed a lower diversity than the active community; however, we demonstrated that the analysis of resting egg bank composition can help detect general community structure patterns.     

Increasing dominance of small zooplankton with toxic cyanobacteria

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Scale‐dependent frequency distributions of plant species in dune slacks: Dispersal and niche limitation

Question: How do distribution patterns change with increasing scale level, and can this shift be attributed to dispersal and/or niche limitation? Location: Dune slacks at the Belgian and North French coast. Method: Frequency distribution patterns of species were tested over different scale levels (ranging from 0.008 to 45 km²). Analyses were executed for the total species pool and for subsets of species with high and low dispersal rates and habitat generalist and specialist species. Results: Species distributions for the total species pool on scale levels larger than 1.5 km² were unimodal, with an overrepresentation of rare species. With decreasing scale level, the proportion of common species increased, leading to weak bimodality. Distributions of subsets of slowly dispersing and habitat specialist species are on all scale levels characterised by a strongly unimodal pattern. The subset of species with high dispersal rates and habitat generalist species has a higher proportion of common species, leading to a significant core peak. Conclusions: On all scale levels both dispersal and niche limitation are hampering the wider distribution of rare species. However, since isolation and habitat heterogeneity are limited on the smaller scale levels, a larger proportion of well dispersing and habitat generalist species is able to occupy a high number of patches, resulting in a significant core peak for the total species pool.     

Development of a quantitative PCR method to explore the historical occurrence of a nuisance microalga under expansion

A number of marine and freshwater harmful algal bloom (HAB) species have colonized new areas and expanded their habitat range in recent years. Nevertheless it is notoriously difficult to establish when colonization first occurred, what the dispersal routes are, and to separate recent invasion from increases in existent but small populations. The freshwater raphidophyte Gonyostomum semen is a nuisance species that has expanded its habitat range and increased in abundance in northern Europe during the past decades. To evaluate to what extent sediments can be used for determining historic occurrence of G. semen, a quantitative real-time PCR method for detecting cysts of this algae was developed. This paper presents a qPCR protocol with a set of primers that are specific to Gonyostomum and with PCR conditions optimized for sediment samples from humic lakes, which are the common habitat of G. semen. With this sensitive method as few as 1.6 cysts per PCR reaction could be reliably quantified, corresponding to 320 cysts per g wet weight sediment. Cysts were present in sediments with ages ranging from years to decades and their persistence allows detection of historic populations up to at least 50 years old. With this qPCR assay it will be possible to trace the presence of G. semen in environments prior to the onset of algae-specific monitoring programs as well as for quantification in water column samples.     

Natural dispersal to sub-Antarctic Marion Island of two arthropod species

Distinguishing between species that are recent natural colonists, recent anthropogenic introductions, or previously unknown, but long-term resident native species, is a challenge for those who manage the conservation of the Antarctic region. Here, we report the discovery of two new arthropod species on sub-Antarctic Marion Island—Nabis capsiformis Germar (Heteroptera: Nabidae) and Tetragnatha sp. (Araneomorphae: Tetragnathidae). On the basis of their habitat use, dispersal abilities, historic biodiversity survey records, and limited information on genetic diversity, we conclude that the colonization events were natural.     

The influence of pool volume and summer desiccation on the production of the resting and dispersal stage in a Daphnia metapopulation

Dispersal is a key process in metapopulations, as migrants genetically connect populations and enable the colonization of empty habitat patches. Sub-populations may differ in their numerical contribution of migrants within a metapopulation. This has strong implications on evolutionary and ecological dynamics and has led to two different hypotheses about the Daphnia metapopulation studied here: the assessment by some authors is that sub-populations contribute equally to the production of migrants, while others have postulated long-lived core populations in large "mainland" habitat patches as the dominant source of migrants. We have studied the resting and dispersal stage (ephippium) in a natural Daphnia metapopulation and in mesocosm experiments, and tested for effects of habitat size and summer desiccation. We found that a 1000-fold increase in rock pool volume resulted on average in only in a 2.8-fold increase in ephippium production. Mesocosm experiments confirmed these results: a 1000-fold increase of the mesocosms' volume resulted in a 7.2-fold increase in ephippium production. Additionally, we showed that ephippium production did not depend on the initial population size. Thus, populations in small pools may contribute only marginal fewer potential migrants in the whole metapopulation than populations in large pools. In a second mesocosm experiment we found that summer desiccation, which is a typical occurrence in small pools, is not detrimental for the populations. Daphnia hatched out of ephippia that were produced earlier within the same season and built up viable populations again. The substantial production of ephippia by populations in small pools suggests that these populations might be important for both the dynamics and global stability of metapopulations.     

Crustacean diversity in relation to the size of water bodies: some facts and problems

SUMMARY.

• 1 Data on the crustacean faunas of 207 lowland water bodies in Yorkshire, involving 125 species, are discussed in relation to site area. Not unexpectedly, large water bodies generally have the most diverse faunas, but the relationship is not a simple one so far as individual species are concerned. While many show a progressive increase in percentage occurrence from small to large water bodies, the reverse is true for others.
• 2 Chydorid cladocerans, of which twenty-one species were recorded, show an unambiguous preference for large water bodies. While differences in habitat diversity appear insufficient to explain the almost seven-fold difference in chydorid representation between ponds and large water bodies, there are also difficulties in attributing the situation to ease, or difficulty, of dispersal. The strategy of firmly attaching resting eggs to substrata employed by some chydorids is more likely to frustrate than to promote dispersal.
• 3 General habits, ecological preferences and feeding habits of the commonest species are analysed in an attempt to clarify the relation of number of species to size of water body and some paradoxical features of dispersal are noted.
• 4 Extrapolation from the data to very large lakes is shown to be misleading. Numerical data, even for a large number of water bodies, are no substitute for knowledge of the ecological requirements and tolerances of individual species.
• 5 Examples are given of the rapid colonization of newly formed ponds by small crustaceans. The relevance of such observations to the theory of island biogeography and to various ecological problems, and the possibility of experimental work using small crustaceans and small ponds are noted.

     

Karyologic observations on the maturation of the summer and winter Eggs of Daphnia pulex and Daphnia middendorffiana

The cladoceran Daphnia middendorffiana is an arctic species able to produce winter eggs which develop parthenogenetically. The cytological study of the maturation of summer and winter eggs of an italian population of this species has shown that both types of eggs undergo only one maturation division of equational type with the expulsion of only one diploid polar body, the same maturation process as had been found in the pseudosexual eggs of a race of Daphnia pulex (Schrader, 1925).—The chromosomes behaviour during the maturation of summer and winter eggs of D. middendorffiana has been compared with that of a population of D. pulex which shows a normal heterogonic cycle.This investigation was supported by the Consiglio Nazionale delle Ricerche (C.N.R.) of Italy.     

Zooplankton ecology and trophic resources for rearing native fish on an agricultural floodplain in the Yolo Bypass California,USA

Out-migrating juvenile Chinook Salmon Oncorhynchus tshawytscha in California’s Central Valley lack frequent access to historical off-channel habitats such as floodplains. However, many regions have agricultural floodplains that may provide habitat value to young salmon. To determine the suitability of agricultural floodplain, this study tested whether winter-inundated rice fields in a historic flood basin in California’s Central Valley could provide adequate food resources for rearing juvenile Chinook Salmon. We examined the suitability of flooded rice fields for three post-harvest habitat types: stubble, fallow, and disced. Soil emergent and pelagic zooplankton communities were compared to determine colonization sources. Winter-inundated rice fields had high densities of zooplankton, which increased over the course of the study. Daphnia pulex, a large-bodied cladoceran and an excellent forage species of juvenile Chinook Salmon, was abundant in our study. Cladocerans colonized via source water while ostracods likely colonized from a soil egg bank. Overall, there was no discernable effect of habitat type on zooplankton community structure or density, except for D. pulex. Our results suggest that flooded agricultural rearing habitat can support juvenile Chinook Salmon based on high densities of zooplankton and other suitable habitat conditions have the potential to support a robust aquatic food web.     

Large-scale spatial ecology of dung beetles

Recent modelling work shows that the composition of local communities can be influenced by the configuration of the surrounding landscape, but many of these models assume that all community members display the same type of extinction‐colonization dynamics. I use Aphodius dung beetles to test the hypothesis that interspecific differences in habitat selection and dispersal capacity may translate into differences in spatial population dynamics, even among closely related species coexisting on the same resource. If this is true, then groups of species with different characteristics would show different responses to landscape configuration. I first divided the area of Finland into a grid, and used collection records to describe regional variation in the Aphodius fauna of open cattle pastures. I then sampled dung beetles on 131 cattle farms, to examine whether the subset of species found on each farm was related to the density of pastures in the surrounding grid square. Finally, I used historical records to analyze changes in dung beetle communities during the last century, when there was great loss of pasture. Overall, I found no relationship between landscape characteristics and the total proportion of the regional species pool that was found on each farm. However, the distribution of species among guilds with different habitat specificity did relate to the configuration of the landscape, and the pattern was most pronounced in a specialists species with limited dispersal. Associations between community structure and landscape configuration were superimposed on two much larger and stronger patterns: a large‐scale latitudinal gradient in regional species richness, and a decelerating gain of species to local communities with an increasing regional species pool. I conclude that ecological variation among community members is a crucial factor in the analysis of local community composition, and that local species richness should always be conditioned on regional richness.