Freshwater Rock Pools Research Articles

Pools ‘on the rocks’: freshwater rock pools as model system in ecological and evolutionary research

Pools 'on the rocks': freshwater rock pools as model system in ecological and evolutionary research Rock pools inarguably exhibit a number of characteristics which make them attractive as a model system in ecological and evolutionary research. They are usually small, pristine, clearly delineated and structurally simple systems that occur on a global scale. They facilitate the quantication of important population and community structuring processes which are often hard or impossible to quantify in larger more complex systems. Basic properties and spatial conguration of rock pools also closely resemble theoretical metapopulation and metacommunity models. Due to the simple morphometry of rock pool basins and the lack of any groundwater interactions, rock pool hydrologies are simple allowing to reliably reconstruct the disturbance regime against which patterns of variation in life histories, population genetics, species diversity and community structure can be interpreted.

Anostracan monopolisation of early successional phases in temporary waters?

The length of the hydrocycle restrains the development of communities in temporary aquatic habitats. Little information is available on the importance of biotic interactions in shaping the communities in these temporary habitats. A common observation in the freshwater rock pool community assembly process is the clearly separated density peaks over time of fairy shrimp (Anostraca) and cladocerans (Anomopoda). Fairy shrimp (Anostraca), the fl agship group and dominant fi lter feeders of temporary waters hatch early after inundation. This contrasts with the occurrence pattern of coexisting cladocerans, which despite higher chances of abortive hatching occur later during the hydroperiod. To study this apparent succession pattern and test the possible presence of a biotic interaction, we set up enclosure experiments in freshwater rock pools in Western Australia and monitored cladoceran (Macrothrix hardingii) densities in the presence of variable densities or absence of fairy shrimp (Branchinella longirostris). The anomopod cladoceran populations decreased with increasing anostracan densities revealing a negative biotic interaction. The competitive dominance of anostracans most probably was mainly due to exploitation competition, with possibly elements of interference competition or predation included. Early hatching and competitive superi- ority may help anostracans in temporary pools to monopolize the habitat with respect to small and/or other fi lter feeding invertebrates. As such they infl uence succession dynamics and invertebrate community structure, making anostracans keystone species of temporary pools.

The role of metacommunity processes in shaping invertebrate rock pool communities along a dispersal gradient

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 m2). 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.

Local structuring factors of invertebrate communities in ephemeral freshwater rock pools and the influence of more permanent water bodies in the region

We used three isolated clusters of small ephemeral rock pools on a sandstone flat in Utah to test the importance of local structuring processes on aquatic invertebrate communities. In the three clusters we characterized all ephemeral rock pools (total: 27) for their morphometry, and monitored their water quality, hydrology and community assemblage during a full hydrocycle. In each cluster we also sampled a set of more permanent interconnected freshwater systems positioned in a wash, draining the water from each cluster of rock pools. This design allowed additional testing for the potential role of more permanent water bodies in the region as source populations for the active dispersers and the effect on the community structure in the rock pools. Species richness and community composition in the rock pools correlated with level of permanence and the ammonia concentration. The length of the rock pool inundation cycle shaped community structure, most probably by inhibiting colonization by some taxa (e.g. tadpoles and insect larvae) through developmental constraints. The gradient in ammonia concentrations probably reflects differences in primary production. The more permanent water bodies in each wash differed both environmentally and in community composition from the connected set of rock pools. A limited set of active dispersers was observed in the rock pools. Our findings indicate that aquatic invertebrate communities in the ephemeral rock pools are mainly structured through habitat permanence, possibly linked with biotic interactions and primary production.

Successional phases and species replacements in freshwater rock pools: towards a biological definition of ephemeral systems

Summary1. In temporary aquatic habitats, time is probably the dominant environmental factor affecting community composition, mainly by setting constraints on colonization success and the replacement of taxa over time. The mechanism and effect of a decreasing inundation period on community development, mostly in terms of truncation, are still poorly documented. The permanent and ephemeral components of temporary communities are expected to be differently influenced by the degree of persistence of the habitat.2. To study the effect of time on invertebrate community assembly and dynamics in a short duration type of temporary aquatic habitat, we monitored 16 ephemeral rock pools which persisted from less than a week to about 1 month at two rock pool sites in semi‐arid south‐eastern Botswana. Data were collected every 2 days during a full inundation cycle.3. All communities were initially assembled by permanent residents recolonizing the habitat from egg banks and were later joined by actively dispersing ephemeral taxa. Species replacements only occurred in two pools. Concurrent with a decrease in the densities of Branchipodopsis wolfi, population sizes of Leberis sp. and Culicidae (Aedes sp. and Anopheles sp.) increased in these pools. Although it was possible to distinguish two successive phases at one rock pool site, community assembly was generally a gradual process determined by dispersal strategies of the inhabitants. Additional rains after initial filling triggered dispersal by ephemeral taxa, mainly Micronecta youngiana and Hydroglyphus infirmus, and positively influenced colonization success.4. Decreasing persistence shortens community development down to a critical point below which lack of time eliminates the possibility of species replacement. Based on these findings, we define ephemeral waters as aquatic habitats lacking species replacements. Other temporary water types have a relatively longer persistence, permitting successional replacement of species.

Temporal patterns of diversity, abundance and evenness for invertebrate communities from coastal freshwater and brackish water rock pools

Aquatic invertebrate data were collected from 49 erosional, Jamaican,rock pools between 1989 and 1998 and used to describe temporal patterns ofspecies diversity. This unique series of pools on the north coast of Jamaica,classified as either brackish (31) or freshwater (18), was used to determinehowdiversity changes over time, whether there was a difference between poolclassifications, and the impacts of environmental variables. Mean communitymetrics (richness, diversity, evenness, abundance) were not significantlydifferent between freshwater and brackish pools. However, there weresignificantdifferences among the eight sampling dates and differences over time dependedonpool classification. Measures of diversity for freshwater pools were relativelyconstant over time, implying little change at the community level. Brackishpools showed significant differences over time in species richness, totalabundance, and evenness implying that community composition and structure werenot static but changed in response to either environmental or biotic changes(possibly initiated by environmental change).Some temporal changes in community metrics could be linked to temporal changesin environmental variables. In brackish water pools, a significant increase inpool salinity between January 1991 and January 1992 corresponded to an increasein species richness, likely due to an increase in marine fauna. Similarly,changes in abundance and evenness corresponded to changes in temperature,dissolved oxygen, and pH. In addition, physicochemical variables used in thisstudy were shown to affect community metrics and those relationships dependedonpool classification. Most relationships between community metrics andenvironmental variables were negative with the exception of Simpson's diversityindex for which positive relationships were found. This may indicate that, aspool conditions become less favorable, a few species flourish and dominate thecommunity.

Are there fine‐scale spatial patterns in community similarity among temporary freshwater pools?

AbstractOne expects greater similarity between communities that are close together in space than between communities that are widely separated. This may be due to similarity in environmental conditions, short‐range dispersal, or both processes together. We examined whether these mechanisms were important in determining the invertebrate communities in a set of temporary freshwater rockpools within an area of 800 m2. Adjacent pools tended to share similar environmental characteristics (conductivity, pH, presence of predatory Salamandra salamandra L. larvae and amount of shade). Community dissimilarity was not strongly related to interpool distance. Environmental variables did not explain a significant amount of variation in community dissimilarity, although differences in pH and depth were the best predictors of community dissimilarity. We conclude that dispersal is not limiting in our study system.

Egg hatching of mosquitoes Aedes caspius and Ae. vittatus stimulated by water vibrations.

Simple laboratory experiments with eggs of wild-caught Aedes caspius (Pallas) and Aedes vittatus (Bigot) mosquitoes (Diptera: Culicidae) demonstrated that egg hatch rates (i.e. percentage hatching daily) increased significantly in response to water vibrations caused by finger-tip drumming on containers of submerged eggs. When disturbed by daily vibrations for only 30 s, eggs hatched sooner than when they remained flooded or were periodically drained and reflooded without agitation. For autogenous Ae. caspius from saltmarsh, egg hatch rates were three- to four-fold greater for groups of 50 eggs than for solitary eggs, possibly due to chemicals (functional kairomones) emanating from other eggs or larvae. For anautogenous Ae. vittatus from freshwater rock-pools, tapping the container daily (for 30 s each 2 h in 8 h) hatched 93% of eggs, compared with only 42% hatch of eggs agitated only when first flooded or 55% hatch of eggs dried and reflooded three times during 17 days without other disturbance. It is concluded that, apart from flooding and other factors, vibrations - simulating the patter of rainfall provide a very significant hatching stimulus for Aedes eggs.

Do Female Common Frogs Choose Their Breeding Habitat to Avoid Predation on Tadpoles?

Predation is an important mortality factor among larval amphibians. Female amphibians may therefore increase their fitness by choosing predator-free reproductive habitats. We studied whether female common frogs choose their breeding habitat in order to minimize tadpole mortality by fish predation. In a paired experimental design we manipulated twelve freshwater rock-pools by introducing adult threespine sticklebacks in them and compared the numbers of reproducing female frogs and surviving tadpoles with those in twelve unmanipulated pools at close distance. All pools had supported a breeding frog population during the two preceding years. Common frog females did not alter their pool choice after the fish introductions. There was no difference in the number of egg batches laid in manipulated and in control pools. The egg laying pattern did not differ qualitatively from that in the two previous years. Laboratory experiments revealed that threespine sticklebacks prey heavily upon young common frog tadpoles and field investigations indicated significantly lowered tadpole survival in pools with sticklebacks. Thus, common frog females did not choose their reproductive habitat to avoid predation on tadpoles. We discuss site tenacity and intraspecific competition among tadpoles as other possible agents affecting female reproductive habitat choice.