Accounting for temporal change in multiple biodiversity patterns improves the inference of metacommunity processes.

In metacommunity ecology, a major focus has been on combining observational and analytical approaches to identify the role of critical assembly processes, such as dispersal limitation and environmental filtering, but this work has largely ignored temporal community dynamics. Here, we develop a "virtual ecologist" approach to evaluate assembly processes by simulating metacommunities varying in three main processes: density-independent responses to abiotic conditions, density-dependent biotic interactions, and dispersal. We then calculate a number of commonly used summary statistics of community structure in space and time and use random forests to evaluate their utility for inferring the strength of these three processes. We find that (i) both spatial and temporal data are necessary to disentangle metacommunity processes based on the summary statistics we test, and including statistics that are measured through time increases the explanatory power of random forests by up to 59% compared to cases where only spatial variation is considered; (ii) the three studied processes can be distinguished with different descriptors; and (iii) each summary statistic is differently sensitive to temporal and spatial sampling effort. Including repeated observations of metacommunities over time was essential for inferring the metacommunity processes, particularly dispersal. Some of the most useful statistics include the coefficient of variation of species abundances through time and metrics that incorporate variation in the relative abundances (evenness) of species. We conclude that a combination of methods and summary statistics is probably necessary to understand the processes that underlie metacommunity assembly through space and time, but we recognize that these results will be modified when other processes or summary statistics are used.

Diel changes in vertical and horizontal distribution of cladocerans in two deep lakes during early and late summer.

Temporal and spatial heterogeneity in the distribution of cladocerans in lakes could be caused by abiotic (wind, water currents) and biotic factors (reproduction, food resources, predation). Diel horizontal and vertical distribution of cladoceran assemblages was studied in two deep lakes (Milada and Most Lakes, Czech Republic) in early (June) and late (September) summer. The objective was to study diel vertical migration (DVM) and diel horizontal migration (DHM) of cladocerans under conditions of different macrophyte cover in littoral areas (rich in Milada Lake, poor in Most Lake) and fish assemblages (non-specialised planktivorous species in Milada Lake, and abundant planktivorous fish - maraena whitefish, Coregonus maraena - in open water habitats in Most Lake). Temporal variations in cladoceran assemblages were reported in both lakes in the two sampling periods. DVM was observed in the two lakes, performed by the most vulnerable species to fish predation (the larger Daphnia spp.), but with different patterns (direct and reverse) probably linked with the local fish community and other biotic and abiotic factors in each lake. Horizontal movements were only observed in Most Lake: D. longispina increase its abundance in open waters at night compared to the littoral points; while Ceriodaphnia spp. showed the inverse pattern. In both lakes, higher densities were often found at night in surface layers, producing a great "diurnal deficit": cladocerans remain undetected in some zones during the day (especially in the littoral areas) moving to surface layers at night.

Tracking environmental changes in restored Mediterranean dune slacks.

Restoration is an ecological tool that aims to recover the prior conditions and functioning of a degraded habitat. Three restoration projects targeted a dune slack system in the Eastern Iberian Peninsula and created a mosaic of ponds restored over three different periods: 1998, 2003 and 2007, the latter coinciding with the start of our study. Restoration works consisted of digging out the pond basin to its original morphometry. We monitored 12 restored ponds (six recent, three intermediate and three older ones) monthly, over four consecutive hydrological years (from 2007 until 2011) characterizing the most important limnological factors in order to disentangle the effects of man-made restoration over time. A multivariate statistical approach was used to detect the environmental trends of these ponds related to their restoration ages. Recently restored ponds tended to converge with older ones by decreasing values of conductivity, pH, oxygen and depth and increasing vegetation cover over time. Detected differences seem to address age-specific processes which increase over time after restoration: silting, salt leaching or an increase in organic matter decomposition. These processes could strongly influence the community build-up and biodiversity therein.