Quantifying ecological filters: the relative impact of herbivory, neighbours, and sediment on an oligohaline marsh

Abstract

The objective of this experiment was to quantify the relative importance of herbivory, interactions with neighbours and sediment addition as filters in controlling the species present in an oligohaline marsh in southeastern Louisiana, USA. We planted 16 species of wetland plants in 3)3 m plots either inside or outside herbivore exclosures, with or without presence of established vegetation, and with or without added sediment. These species, representing 12 families and diverse morphologies, included herbaceous and woody plants. At the end of the growing season above-and below ground biomass were measured. In cleared plots (no neighbours) inside herbivore exclosures, 12 of the 16 species grew well, indicating that they could tolerate the physical conditions in the habitat. Competition significantly reduced the biomass of four of these species (A. calamus, C. occidentalis, P. hemitomon, P. cordata ), suggesting that it is the strongest species-specific filter operating in the marsh. These results confirm the general consensus that competition from existing plants is the strongest filter operating in high biomass habitats, and further imply that competition has the potential to remove 33% of the species from the community. Facilitation occurred for one species, R. corniculata. Herbivory had the largest general effect of reducing biomass, as determined in the full ANOVA model, but on a species-specific basis, significantly reduced the biomass of only two species (T. distichum, T. domingensis ). These results support the emerging view that herbivory is an important filter in coastal wetlands. Although several other studies have argued for the importance of sedimentation in controlling plant species composition in wetlands, we found no effect of sediment addition. Competition and herbivory appear to be two critical biological filters that control plant composition of coastal wetlands, and they must be considered in future studies and restoration efforts along the Gulf of Mexico.

Plant community functional shifts in response to livestock grazing in intermountain depressional wetlands in British Columbia, Canada

“…Vegetation of ungrazed depressional wetlands is typically relatively species poor and is characterized by dense stands of tall, clonal, competitively dominant species. Competition for light is likely to be an important constraint in such a system (Twolan-Strutt and Keddy, 1996;Geho et al, 2007), as is the ability to successfully colonize gaps (Carlyle and Fraser, 2006). This is attested by the near-ubiquity of tall and rhizomatous species at ungrazed sites in the study.…”

Herbivore regulation of plant abundance in aquatic ecosystems

“…As there is no universally accepted distinction between pond and lake (Sayer, 2014), for the purposes of our study we included ponds within the lake category. Whilst herbivore consumption rates may increase with body mass to a power of <1.0 (van Gils, Gyimesi & Van Lith, 2007;Wood et al, 2012b), consumption is only one mechanism through which herbivores affect plant abundance, with others including trampling, and herbivore-induced changes in nutrient availability (e.g. through faecal deposition) and light climate (Mitchell & Wass, 1996;Hobbs & Searle, 2005).…”

Emergence of Summertime Hypoxia and Concurrent Carbonate Mineral Suppression in the Central Bohai Sea, China

“…However, a geographic information system-based study (supported with satellite imagery analyses) suggested that coastal reclamation shortened the natural coastline of Bohai Sea from 1,397 km in 1990 to 561 km in 2014 (Hou et al, 2018). According to some researchers (e.g., Comín et al, 2014;Crumpton, 2001;Geho et al, 2007), these changes may decrease the nutrient filtration effect of coastal wetlands. Moreover, the local marine aquaculture yield increased by 20 times from 1985 to 2002, directly discharging a large amount of nourished sewage into the Bohai Sea (Cui et al, 2005).…”