ponds and pools as model systems in conservation biology, ecology and evolutionary biology

Copyright # 2005 John Wiley & Sons, Ltd.

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS

Aquatic Conserv: Mar. Freshw. Ecosyst. 15: 715–725 (2005)

Published online in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/aqc.748

Ponds and pools as model systems in conservation biology,ecology and evolutionary biology

LUC DE MEESTER*, STEVEN DECLERCK, ROBBY STOKS, GERALD LOUETTE,FRANK VAN DE MEUTTER, TOM DE BIE, ERIK MICHELS and LUC BRENDONCK

Laboratory of Aquatic Ecology, Katholieke Universiteit Leuven, Leuven, Belgium

ABSTRACT

1. Ponds and pools, broadly defined in this paper to include all small and shallow standing watersthat permanently or temporarily contain water, are numerous, diverse and important from aconservation point of view. We here argue that ponds and pools offer powerful potential for studiesin ecology, evolutionary biology and conservation biology.2. An outline is given of the characteristics of pools and ponds that make them good model

systems for large-scale surveys and hypothesis testing through experimental manipulation. Suchstudies will not only increase understanding of community and genetic structure, as well as ofpatterns of biodiversity, in small aquatic habitats themselves, but may also contribute significantly totesting general theory.3. These merits are illustrated by the recent progress on the understanding of the relative

importance of local versus regional factors in structuring populations and communities, as well as ofthe impact of hydroperiod on community and ecosystem functioning.Copyright # 2005 John Wiley & Sons, Ltd.

KEY WORDS: ponds; temporary pools; aquatic biodiversity; connectedness; hydroperiod; conservation;

community structure

INTRODUCTION

Much attention in conservation biology is directed towards large-scale coastal and inland ecosystems, suchas vast wetlands (e.g. famous tropical floodplains), lakes and river ecosystems, coral reefs, rain forests,Antarctica, and marine systems (e.g. Meffe and Carroll, 1997). Although the attention to the preservationof these large-scale ecosystems is clearly warranted, it has led to a general neglect of small-scale landscapeelements, such as freshwater ponds and pools. Yet, it has been shown that these small ecosystemscontribute disproportionately to regional diversity, largely because of their high b diversity (compositionaldissimilarity among sites) (Oertli et al., 2002; Williams et al., 2004). This high contribution to regional

*Correspondence to: Luc De Meester, Laboratory of Aquatic Ecology, Katholieke Universiteit Leuven, Charles de Beriotstraat 32,3000 Leuven, Belgium. E-mail: [email protected]

diversity is due both to the fact that ponds often strongly differ in species composition amongst each other,and to the occurrence of species that are specific to small ponds and pools. For instance, in the particularcase of temporary pools, specific adaptations are required to deal with variable and often extreme localenvironmental conditions, including time stress for development and reproduction, and mechanisms tobridge dry periods. This results in very specific biota (Wiggins et al., 1980; Brendonck and Persoone, 1993;King et al., 1996; Simovich, 1998). In addition, small landscape elements have important ecosystemfunctions. They are, for instance, important in providing migration corridors and stepping stones for biota(Merriam, 1991), thus fulfilling an important ecological role at the landscape level (e.g. in a metapopulationand metacommunity context (Jeffries, 1994; Caudill, 2003)). To conserve biota at the landscape level,attention to small-scale systems is thus needed for two reasons: because of their own specific characteristicsand communities, and because of their role in metapopulation and community dynamics. In order to ensurethe preservation of the biodiversity and ecosystem services of ponds and pools, however, the processescontributing to their specific characteristics must be understood. The high b diversity of ponds and pools isno doubt related to their high diversity in characteristics (e.g. length of hydroperiod, trophic (food web)structure, abundance and species composition of macrophytes, disturbance by cattle), chance effectsassociated with their isolated nature, and second-order effects (e.g. effects of the presence or absence ofkeystone species on the trophic structure of the system, cf. Scheffer et al., unpublished). There is, however, aneed for well-designed experiments to verify the relative importance of these and other processes. There isalso a need for stringent testing of the degree to which different types of standing waters – for instance alonga size gradient – show a pattern of nestedness, as this has important conservation implications (e.g. Oertliet al., 2002; Snodgrass et al., 2000b; Baber et al., 2004).

Ponds and pools are broadly defined here as small and shallow water bodies, the difference betweenponds and pools being that ponds permanently hold water whereas pools dry out, either regularly, yearly orevery few years. This definition resembles the one given by Davies and Day (1998). It is difficult to specifyan upper size limit to what is called a pond and when it should be called a shallow lake. As argued also byS�ndergaard et al. (2005), ponds and shallow lakes share many characteristics in terms of structure andfunction, and the transition zone between the two types of habitats is very gradual. An important aspectmay be that as size increases, wind action may have a higher impact on the system. Similarly, small systemsare less likely to harbour stable populations of benthivorous fish, which have an important structuring roleand may suppress the development of submerged vegetation.

Pinpointing ponds to a size limit of, for instance, 1 to 5 ha, may sound logical, but remains artificial, andis perhaps counterproductive to views on the structure and functioning of these systems.

In this contribution, we want to add an additional dimension to the services provided by pools andponds, and an additional reason to cherish and preserve these small-scale ecosystems: their scientific value.Ponds not only need to be studied for the sake of understanding their own structure and function, but alsocan be used as excellent model systems for hypothesis-testing in ecology, evolutionary biology and natureconservation (see also Blaustein and Schwartz (2001) for a similar plea with respect to temporary pools).

WHY ARE PONDS AND POOLS GOOD MODEL SYSTEMS?

There are several reasons why ponds and pools are attractive model systems for research in ecology,evolutionary biology and conservation biology:

1. Ponds and pools are abundant. Although there are a number of regions in which ponds are relativelyrare, small-scale aquatic habitats are generally abundant throughout the world. This ensures that it ispossible to carry out field surveys or field experiments covering broad latitudinal, longitudinal andaltitudinal gradients, with a potential for good coverage along any desired ecological gradient. Because of

L. DE MEESTER ET AL.716

Copyright # 2005 John Wiley & Sons, Ltd. Aquatic Conserv: Mar. Freshw. Ecosyst. 15: 715–725 (2005)

their large number, it is relatively easy to find a sufficiently high number of pools along the whole spectrumof an ecological gradient. This allows the proper application of statistical tests.

2. There is a very wide variety in pond types. Ponds and pools indeed span a very broad range ofecological gradients, e.g. in terms of the length of the hydroperiod, size, and nutrient concentration. Thisallows the study of the associations between their characteristics (e.g. biodiversity, community composition,food-web structure) and these gradients. Because pools are numerous in many regions, there is a highprobability that the different subsections of the studied gradients will be well represented.

3. Ponds and pools are often threatened by direct habitat destruction (filling up of ponds; deepening ofephemeral pools so that they become permanent) or other forms of strong human impact (e.g. pollution,eutrophication, introduction of exotic species, trampling by cattle). Within and among regions, it is oftenpossible to identify pond ecosystems with widely different anthropogenic stress. As small ponds and poolsare characterized by a high aquatic–terrestrial contact zone, they may be ideal sentinel systems that canreflect changes in larger-scale ecosystem health. Owing to their small sizes and simple community structure,small aquatic ecosystems may also function as early warning systems for long-term effects on larger aquaticsystems (e.g. changes in hydroperiod due to global change).

4. Ponds and pools are very well delineated in the landscape, being aquatic ‘islands’ in a terrestriallandscape. As such, the boundaries of local populations and communities are easily determined. As a result,they fit nicely into the basic scheme of metapopulation and metacommunity theory: for obligatory aquaticorganisms, ponds and pools are suitable patches in an unsuitable habitat matrix. Landscape characteristics(e.g. number, size and permanence of neighbouring ponds, regional species richness) and aspects ofconnectivity (e.g. presence of and dispersal rates through direct connections, Brendonck and Riddoch,2000a; Michels et al., 2001) are also relatively easy to quantify, which makes ponds excellent model systemsfor quantitative research on metacommunities (e.g. Conrad et al., 1999; Caudill 2003; Cottenie et al., 2003;McAbendroth et al., 2005).

5. Because of their small size, ponds and pools are relatively easy to sample in a repeatable, quantitativeand representative way. Whereas a pooled sample at, for instance, three random locations in a 100-m2

system will be considered representative by many people, one may argue whether an equal number ofrandomly selected sampling stations can yield a representative measure of the abiotic and bioticcharacteristics of a 100-ha lake. Especially in biodiversity studies, sampling large systems in anencompassing way is difficult. In comparison with larger systems, small ponds and pools also tend to beless heterogeneous in space, and show less interference from wind effects (for example). The ease with whicha large number of systems can be sampled offers great potential for field surveys, especially with respect tothe ever-recurrent compromise between the need for standardization and deep-reaching, quantitativeanalyses on the one hand and the need for many study systems on the other. It should be noted that year-to-year variability in small water bodies may be higher than in larger-sized systems, and this needs to beincorporated into the design of field studies.

6. As pond and pool communities are relatively simple, they are amenable to standardized experimentalmanipulation using in situ enclosures or even whole-ecosystem approaches. This allows replicatedexperiments to be carried out under relevant field conditions (e.g. Shurin, 2000; Jeffries, 2002; Cottenie andDe Meester; 2004; Louette et al., in press). Small ponds and pools can also easily be mimicked as a whole bydigging out new systems (Blaustein and Schwartz, 2001; Jeffries, 2002). In a similar approach, one may alsotake advantage of the opportunities offered by the many ponds that are created as part of natureconservation programmes (e.g. Fairchild et al., 2000; Louette and De Meester, 2005).

7. Experimentation inevitably implies simplification of natural systems and phenomena. Their relativesimplicity allows pond ecosystems to be relatively well mimicked in mesocosms and containers, increasingthe scope for large-scale replicated experimental work, both in outdoor facilities and in the laboratory(Shurin, 2001; Ebert et al., 2002; Williams et al., 2002; Chase, 2003; Hall et al., 2004; Louette andDe Meester, unpublished). This allows complex experimental designs and the testing of hypotheses that

PONDS AS MODEL SYSTEMS 717


need large-scale replication (Rowe and Dunson, 1994; Moss et al., 2004). Moreover, it allows testing of theeffects of anthropogenic stressors such as pesticides and global warming, which is not feasible at the whole-pond level (DeNoyelles et al., 1982; Hardersen et al., 1999; Boone and James, 2003; but see Lahr, 1998).

Admittedly, ponds and pools cannot be considered to be stand-in model systems for all kinds ofecosystems, and there are obvious limitations to the conclusions that can be drawn from experimentalstudies on them. Complexity of community structure and trophic relationships is one issue. Although thereis the possibility to study quite complex interrelationships at the scale of an individual pond, the potentialfor complex interactions is obviously higher in larger systems. Yet, whereas ponds and pools areintrinsically small-sized ecosystems, it should also be recognized that shallow lakes are structurally verysimilar to ponds. Thus, size as a limitation in studying, for instance, relationships of certain variables withhabitat size, can be largely alleviated by including larger shallow lakes. One can easily span a size range ofmore than 106 by studying pools of less than 1m2 to shallow lakes of 1 km2.

The next sections discuss some recent progress in the knowledge of ecological theory and natureconservation issues gained by means of small aquatic model systems. The paper illustrates how thecharacteristics of ponds were used to tackle two general questions: the relative importance of local andregional factors in explaining community and genetic structure, and the importance of hydroperiod instructuring communities.

LOCAL AND REGIONAL INFLUENCES ON COMMUNITY AND GENETIC STRUCTURE

What are the major driving forces of community structure and diversity, and what are the steering processesbehind the observed genetic structure and diversity? Community assemblage can be influenced by both localand regional factors. Regional factors refer to characteristics of the region that may affect localcommunities. In the first place, this includes characteristics that directly influence the likelihood ofindividuals or species reaching a given habitat (connectedness, abundance of source habitats, characteristicsof the regional species pool). For a given taxon, these regional characteristics result in different rates ofdispersal, ranging from strong dispersal limitation to mass transport effects (Leibold et al., 2004). Regionalfactors also include large-scale environmental conditions that affect all systems in a region (e.g. land-usepatterns), and thus determine the regional species pool. Among local environmental factors, both theabiotic environment as well as biotic interactions (competition, predation, parasitism, mutualism) may beimportant. Shurin (2000, 2001) has carried out both field and experimental work to disentangle the impactof local and regional factors on community structure of zooplankton in ponds. Whereas his work focusedon isolated and aged ponds (>10 years old), Cottenie and De Meester (2004) performed similarexperiments in strongly connected ponds, and Louette et al. (in press) focused on young ponds (1–2 yearsold). All these experiments were done in enclosures or containers established under field conditions, inwhich inocula from the regional species pool were added to experimental units which either did or did notcontain the local resident communities. The basic design of these experiments is inspired by transplantexperiments, a technique routinely applied in evolutionary biological research. The results of all thesestudies suggest that local factors are important in structuring local zooplankton communities. Morespecifically, biotic interactions with local zooplankton communities strongly influenced establishmentsuccess of new immigrants. Cottenie and De Meester (2004) observed that community structure wasstrongly driven by the presence of predators (fish) and macrophytes (structural diversity and shelter frompredation). Species sorting was efficient and repeatable. Strong impact of local conditions has also beenobserved in other organism groups such as amphibians (e.g. Skelly, 1995; Skelly et al., 2002), andmacroinvertebrates (e.g. McPeek, 1990; Wissinger et al., 1999; Stoks and McPeek, 2003). In these othergroups, only Urban (2004) compared the relative impact of regional and local processes in explaining the



structure of a freshwater pond amphibian and macroinvertebrate metacommunity. In this study, regionalprocesses were of minor importance, while the local variable hydroperiod best explained communitystructure. None of these results has been obtained using model systems representing truly ephemeralhabitats. It remains to be tested to what extent local factors have a similarly important impact oncommunities in ephemeral and temporary pools, and whether the relative impact of local versus regionalfactors remains the same over a permanence gradient of the ponds and pools. As for the nature of the mostdominant local factors, Schneider and Frost (1996) have shown that the relative importance of abiotic andbiotic local factors changes over the hydroperiod gradient with biotic control becoming more importantwith increasing level of permanence.

The fact that the above-mentioned studies show an important impact of local factors does not imply thatregional factors and dispersal limitation are not important. Jenkins and Buikema (1998) observed thatzooplankton communities in a set of similar, artificial, newly created ponds differed strongly because ofchance events associated with colonization, implying dispersal limitation. Also, in a set of stronglyconnected ponds, the pattern of connectedness had an impact on local community structure (Cottenie et al.,2003; Cottenie and De Meester, in press), whereas connectedness by itself increased local taxon richness(Cottenie and De Meester, 2003). Importantly, dispersal may enhance the efficiency of species sorting. As itensures that the right species arrive in the right habitats, it allows local communities to adjust better to thelocal conditions (Shurin, 2001).

Dispersal limitation introduces variation in community composition, as is shown for zooplankton byJenkins and Buikema (1998) and Caceres and Soluk (2002) and for macroinvertebrates by Wilcox (2001).Part of this variation is stochastic in nature. Stochasticity plays a role at two levels. First, not all speciesreach all suitable habitats, and which of the suitable habitats are reached is partly determined by chance.Second, chance also plays a role with respect to the order in which a series of species arrive in a givenhabitat. If priority effects are important, the sequence of species arrival may have strong effects oncommunity composition. Louette and De Meester (unpublished) showed a strong impact of priority effectson the final cladoceran zooplankton community in a manipulative artificial pond experiment. Communitycomposition was also strongly dependent on whether there was a predator (Chaoborus) in the containers,showing a clear interaction between priority effects and species sorting.

Relatively few parallel experiments have been carried out to investigate the relative impact of local andregional factors at the level of individual populations. Indeed, the genetic structure of a population may besimilarly influenced by both local and regional factors as the local community structure. In a study on thesame set of strongly connected ponds as studied by Cottenie et al. (2003), Michels et al. (2001) documentedthe population genetic structure of local populations of the cladoceran Daphnia ambigua. Two keyobservations were that the pattern of genetic variation reflected the spatial position of the populations inthe system, and that, even in the face of mass transport of individuals, local populations maintained theirgenetic identity. In a follow-up paper focusing on an ecologically relevant trait (predator-avoidancebehaviour), Michels and De Meester (2004) observed that clones isolated from different ponds differed intheir behaviour in accordance with the hypothesis of local genetic adaptation. In general, pond populationsof zooplankton are genetically strongly differentiated (e.g. Hebert, 1987; De Meester, 1996a; Brendoncket al., 2000). Brendonck et al. (2000), for instance, showed significant patterns of isolation by distance inlarge branchiopods at individual rock-pool sites with clusters of close-set pools, and reported strong geneticdifferentiation, despite the fact that dispersal among pools by means of overflowing resting eggs can beabundant (Brendonck and Riddoch, 2000a). The high levels of genetic differentiation can be due to geneticdrift effects (Vanoverbeke and De Meester, 1997), founder events (Boileau et al., 1992; Brendonck et al.,2000) or processes associated with strong local selection pressures (De Meester, 1996a; Declerck et al.,2001). The emerging picture to explain the observed patterns of genetic differentiation among pondpopulations has been synthesized in De Meester et al. (2002), and is reminiscent of the processes outlinedabove for explaining community structure: an important impact of local selection, strong founder events,



combined with dispersal limitation at specific scales. This parallel between processes structuring communityand population genetic structure is intriguing, and warrants joint studies. Species sorting (community level)and natural selection (population level) are essentially very similar processes, but acting on different levelsof biological organization. The same holds for priority and founder effects.

The above patterns and results obtained in studies on zooplankton should not be taken as a paradigm forother organism groups, as they are dependent upon specific characteristics, such as the fact thatzooplankton is obligatory aquatic, and that most zooplankton species have the ability to produce restingeggs. When considering other groups such as phytoplankton, protozoa and bacteria, we predict that theimportance of local interactions may even be higher, as we expect less dispersal limitation for theseorganism groups and a more efficient response to species sorting and natural selection because of theirshorter generation times. Strong species sorting has indeed been shown for protozoan and rotifercommunities using microcosm experiments (Kneitel and Chase, 2004). On the other hand, whenconsidering other groups such as amphibians and many macroinvertebrates, the expectations changedramatically. Their generation times are much longer, and they have terrestrial phases that allow a totallydifferent pattern of dispersal, in which active habitat choice and homing behaviour may play an importantrole in structuring communities and populations (e.g. McPeek, 1989; Resetarits, 2001; Rieger et al., 2004).For these groups, among-pond variation in species richness and taxon composition of ponds at the samepoint along a habitat gradient may result from a combination of dispersal limitation, priority effects, activehabitat choice and species sorting due to local biotic conditions.

VARIATION IN COMMUNITY AND GENETIC STRUCTURE ALONG

A HYDROPERIOD GRADIENT

One of the key environmental gradients structuring communities in pond systems is the hydroperiodgradient (Schneider and Frost, 1996; Wellborn et al., 1996; Brendonck and Williams, 2000). Hydroperiodmay induce a race against time and exerts a strong impact on species sorting and selection gradients. Itinfluences species and genotype composition in two ways: if the hydroperiod is too short, some species (orgenotypes) cannot survive or reproduce in a given pool (Schneider and Frost, 1996; Pyke, 2002); for others,the short hydroperiod is expected to influence the optimum along the trade-offs between growth rate andcompetitive strength, predator defence strategies, and adult fitness (Wellborn et al., 1996). Sincehydroperiod in the first place will interfere with organisms with long generation times, intermittent andephemeral pools will first tend to exclude predatory species such as most fish and large invertebrates.Therefore, changes in hydroperiod have important second-order effects, as they may greatly change thepattern and strength of biotic interactions (Schneider and Frost, 1996). This induces dramatic changes incommunity structure. Certain groups of organisms, such as the large branchiopods, many amphibians andaquatic insects, are dependent on the absence of fish or even on the absence both of fish and of largeinvertebrate predators (Jeffries, 1996; Brendonck et al., 2002; Stoks and McPeek, 2003). As such,intermittent pools are an important habitat type for nature conservation, as they harbour species thatcannot survive in more permanent habitats (Nicolet et al., 2004).

Overall, owing to differential selection imposed by predation and hydroperiod across the hydroperiodgradient, four different community types linked with the following habitats can be distinguished: ephemeralpools without large invertebrate predators, temporary pools with large invertebrate predators, permanentfishless ponds and lakes, and permanent fish ponds and lakes (Snodgrass et al., 2000b; Stoks and McPeek,2003). If consistent across taxa, a rule of thumb for conservation planning would be to maintain habitats ofall four types within a region (Snodgrass et al., 2000a, 2000b). However, a recent study showed a highdegree of nestedness for amphibian and macroinvertebrate assemblages along this gradient (Baber et al.,2004; but see Urban 2004). These results were attributed to the increased colonization rates and decreased



extinction rates associated with increasing hydroperiod, and to concomitant increases in wetland size,habitat heterogeneity/complexity, and possibly water temperature. In this study, the impact of predatoryfish on species richness and composition of amphibians and macroinvertebrates was found to be relativelyminor. Also, Gunzburger and Travis (2004) questioned the existence of an increasing gradient of predationpressure from temporary to permanent aquatic habitats for amphibians. The controversy generated bythese studies reveals the need for more studies to generate a predictive framework coupling traits of certaintaxa with the pattern of species turnover along the gradient. Understanding the degree of nestedness isimportant, as high degrees of nestedness imply that protection of larger, more permanent ponds may bemore important for conserving native biological diversity than protection of smaller, non-permanentponds. Indeed, whereas several studies showed along the hydroperiod gradient that larger pondscontributed the most to regional diversity (Baber et al., 2004, Eitam et al., 2004), non-permanent andespecially ephemeral pools are generally acknowledged to be used by several species of conservationconcern that often do not occur in larger and more permanent ponds (e.g. Wiggins et al., 1980; Brendonckand Persoone, 1993). We must, indeed, be warned by cases where not considering the qualitative aspects ofthe communities to be sacrificed may result in serious loss of the particular fauna endemic to temporaryhabitats. For instance, King (1998) estimated that the loss of between 50% and 85% of the typical vernalpool habitat in California resulted in the extinction of between 15% and 33% of the original vernal poolcrustaceans since the 1800s.

Given the importance of a life phase that can survive dry periods for obligatory aquatic organisms livingin temporary waters, the structure and function of dormant propagule banks can be expected to havepronounced ecological and evolutionary consequences in these systems (Brendonck and De Meester, 2003).Persistence of populations in temporary pools not only depends on maturation rate but also critically relieson specific egg-bank characteristics such as the information used to trigger hatching, hatching fraction, andlong-term viability of the dormant eggs. The size of the egg bank reflects the success of the particular speciesin a pool or pond, and gives an indication of its buffering capacity to hedge against demographiccatastrophes in unsuccessful growing periods (Hairston, 1996; Brendonck and Riddoch, 2000b).Theoretical models have also indicated the importance of egg banks in the coexistence of species andgenotypes. The egg bank indeed functions as a filter whereby, when different species/genotypes are favouredat different moments (Templeton and Levin, 1979), a storage effect (Warner and Chesson, 1985)compensates for the effects of an unfavourable growth season for a certain species/genotype with a goodreproduction at favourable moments and so may delay extinction indefinitely. This process eventually leadsto the coexistence of a greater number of genotypes/species than can be explained by traditional models.These insights throw a new light on the interpretation of diversity, occurrence and biogeographical patternstaking into consideration the important benthic resting component of pond and pool communities(Brendonck and Williams, 2000; Brendonck and De Meester, 2003). Although temporal segregation duringone growing cycle is not very likely in ephemeral pools and ponds, conditions may change from hydrocycleto hydrocycle within one year or among subsequent years, so that the storage effect may also take place insuch habitats.

Relatively few studies looked at patterns of intraspecific genetic differentiation along the hydroperiodgradient. One reason for this may be that many species only occupy part of the gradient. A distinctionshould also be made between species that do and species that do not have a terrestrial life-phase that allowsdispersal among ponds from one generation to the other. For the former type of organisms, most researchhas focused on amphibians. The emerging pattern is that of little or no differentiation among ponds withdifferent hydroperiod (Loman, 2003). The same may hold for macroinvertebrates. Studies on the damselflyLestes viridis showed no population differentiation between temporary and permanent ponds with regard toallozymes (De Block et al., 2005) or life history (De Block and Stoks, 2004). In contrast, populationdifferentiation in antipredator behaviour among permanent ponds with and without fish has been shownfor Gammarus pulex (Abjornsson et al., 2004), an organism without a terrestrial life-phase. In such cases,



maintaining ponds of several types within a region will be necessary to preserve key genetic variation withinspecies. Also in zooplankton, there is ample evidence for intraspecific among-populational geneticdifferentiation in relation to predator stress (e.g. De Meester, 1996b).

SYNTHESIS

This paper has illustrated the potential of small aquatic systems to be used as models to tackle generalquestions in ecology and evolutionary biology. The issues raised also have important consequences withrespect to nature conservation management and policy. The mechanisms explaining high regional diversity,the importance of connectedness, patterns of nestedness, the presence and characteristics of dormantpropagule banks, etc. are key issues to be considered for the management of biodiversity. Small aquatichabitats are a case at hand for which these aspects should be incorporated in any master plan aimed at theconservation of aquatic biodiversity, and offer great potential for an in-depth study both of patterns and ofmechanisms explaining the patterns.

ACKNOWLEDGEMENTS

We thank Beat Oertli and his coworkers for organizing a very inspiring European Pond Workshop. This work wasfinancially supported by BELSPO project MANSCAPE and EU FP6 IP project ALARM (GOCE-CT-2003-506675).S.D., R.S. and E.M. are postdoctoral researchers and F.V.d.M. is a Ph.D student with the National Fund for ScientificResearch, Flanders (FWO); G.L. is a PhD student with the Institute for the Promotion of Innovation by Science andTechnology in Flanders (IWT).

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ponds and pools as model systems in conservation biology, ecology and evolutionary biology

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