Patrick Grillas

Bio: Patrick Grillas is an academic researcher from Ariès. The author has contributed to research in topics: Wetland & Plant community. The author has an hindex of 26, co-authored 78 publications receiving 2236 citations.

Invertebrate community patterns in Mediterranean temporary wetlands along hydroperiod and salinity gradients

Abstract: 1. Temporary aquatic habitats often are inhabited by a unique fauna and flora and contribute significantly to regional diversity. Temporary wetlands around the world are disappearing rapidly. The individual and interacting impacts of factors influencing community structure and dynamics in temporary wetlands are not always well known. 2. Camargue wetlands are mainly characterized by variable salinity and hydroperiod. The individual and combined impacts of these local factors, together with regional variables, on invertebrate communities remain unknown. We therefore characterized and sampled invertebrates in 30 temporary wetlands along salinity and hydroperiod gradients in the Camargue (Southern France) 3, 5 and 7 months after inundation. 3. Over the three sampling occasions, a total of 17 cladoceran species and 49 macroinvertebrate taxa were identified. Hydroperiod and salinity were the most important variables explaining variation in taxonomic composition and can be considered key factors shaping the invertebrate communities in Camargue wetlands. The impact on taxon richness was significantly positive for hydroperiod but significantly negative for salinity. Regional factors had no significant effect on the structure of the studied invertebrate communities, suggesting that dispersal was not limiting and that species sorting was the most important structuring process. 4. The results of this study suggest that the combined and interacting effects of salinization and hydrological modification of Mediterranean temporary wetlands (due to water management, climate change, etc.) can result in reduced diversity in large numbers of Mediterranean wetlands and induce a considerable decline in regional diversity of aquatic invertebrates.

Seed bank dynamics and coexistence of annual macrophytes in a temporary and variable habitat

Abstract: The seed bank dynamics of annuals in two Mediterranean temporary marshes were studied in order to investigate the impact of the disturbance regime on coexistence. The disturbance regime is made up of drought periods in the marshes and of predation. The density of diaspores buried in the sediment was measured in 4 consecutive years together with the biomass produced during two growing seasons. The total density of diaspores in the sediment varied markedly from year to year but always remained at a high level for all species (between 73000 and 800000 per m 2 ). These perennial seed banks allowed the populations to be maintained despite two successive years without any reproduction. In experimental conditions, the seed bank was not depleted after the sediment samples had been submerged during 5 successive periods. The majority of the seedlings emerged as soon as the first period of flooding and temporary droughts stimulated the germination of Zannichellia spp. and Ranunculus baudotii. The decrease in the number of seeds buried in the soil was essentially due to germination. This was stronger when the seeds were recently produced and situated at the surface of the sediment. The seed density varied only slightly with the depth of the marsh, except in the case of Ruppia maritima. The seed bank is highly variable on a spatial microscale but no aggregation pattern could be demonstrated. In the field, the biomass of a population generally appeared not to be limited by the availability of the diaspores, notably because of the ability to propagate vegetatively which is shown by all species studied. Similarly, a high vegetative biomass does not guarantee a high reproductive output as the droughts occur in a density-independent way. The success of a species is related to the interaction between its life history traits and the environmental conditions met each year. The macrophyte communities we studied function in non-equilibrium, with patterns close to those described in lottery models of coexistence. Establishment, growth and reproduction fluctuate strongly from one year to another for all species, in a partially asynchronous way. This would enable competitive exclusion to be indefinitely delayed. The seed bank introduces a storage effect by magnifying the effect of the favourable years in comparison with the bad years.

Dispersal of freshwater invertebrates by large terrestrial mammals: a case study with wild boar (Sus scrofa) in Mediterranean wetlands

Abstract: SUMMARY 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.

Global variation in the beta diversity of lake macrophytes is driven by environmental heterogeneity rather than latitude

Abstract: Additional co-authors: Gana Gecheva, Patrick Grillas, Jennifer Hauxwell, Seppo Hellsten, Jan Hjort, Mark V. Hoyer, Agnieszka Kolada, Minna Kuoppala, Torben Lauridsen, En‒Hua Li, Balazs A. Lukacs, Marit Mjelde, Alison Mikulyuk, Roger P. Mormul, Jun Nishihiro, Beat Oertli, Laila Rhazi, Mouhssine Rhazi, Laura Sass, Christine Schranz, Martin Sondergaard, Takashi Yamanouchi, Qing Yu, Haijun Wang, Xiao‒Ke Zhang, Jani Heino

The Relationship Between Productivity and Species Richness

Abstract: ▪ Abstract Recent overviews have suggested that the relationship between species richness and productivity (rate of conversion of resources to biomass per unit area per unit time) is unimodal (hump-shaped). Most agree that productivity affects species richness at large scales, but unanimity is less regarding underlying mechanisms. Recent studies have examined the possibility that variation in species richness within communities may influence productivity, leading to an exploration of the relative effect of alterations in species number per se as contrasted to the addition of productive species. Reviews of the literature concerning deserts, boreal forests, tropical forests, lakes, and wetlands lead to the conclusion that extant data are insufficient to conclusively resolve the relationship between diversity and productivity, or that patterns are variable with mechanisms equally varied and complex. A more comprehensive survey of the ecological literature uncovered approximately 200 relationships, of which 3...

PERFORMANCE COMPARISONS OF Co-OCCURRING NATIVE AND ALIEN INVASIVE PLANTS: Implications for Conservation and Restoration

Abstract: ▪ Abstract In the search to identify factors that make some plant species troublesome invaders, many studies have compared various measures of native and alien invasive plant performance. These comparative studies provide insights into the more general question “Do alien invasive plants usually outperform co-occurring native species, and to what degree does the answer depend on growing conditions?” Based on 79 independent native-invasive plant comparisons, the alien invaders were not statistically more likely to have higher growth rates, competitive ability, or fecundity. Rather, the relative performance of invaders and co-occurring natives often depended on growing conditions. In 94% of 55 comparisons involving more than one growing condition, the native's performance was equal or superior to that of the invader, at least for some key performance measures in some growing conditions. Most commonly, these conditions involved reduced resources (nutrients, light, water) and/or specific disturbance regimes. I...

Horticulture as a Pathway of Invasive Plant Introductions in the United States

Abstract: There must have been plenty of them about, growing up quietly and inoffensively, with nobody taking any particular notice of them…. And so the one in our garden continued its growth peacefully, as did thousands like it in neglected spots all over the world…. It was some little time later that the first one picked up its roots and walked. John Wyndham, The Day of the Triffids