The Interactive Effects of Pulsed Grazing Disturbance and Patch Size Vary among Wetland Arthropod Guilds

Abstract

Pulse disturbances and habitat patch size can determine community composition independently or in concert, and may be particularly influential on small spatial scales for organisms with low mobility. In a field experiment, we investigated whether the effects of a pulsed disturbance that simulated a grazing event varied with habitat patch size. We focused on the short-term responses of multiple co-occurring emergent salt marsh arthropods with differing levels of mobility and dispersal potential. As part of a marsh restoration project, two types of emergent marsh structures were created: small circular mounds (0.5 m diameter) separated by several meters of aquatic habitat, and larger, elongated terraces (>50 m long). Study plots (0.25 m2) were established on both structures; in a subset of plots, we simulated a pulsed grazing disturbance event by clipping the aboveground tissue of emergent plants, primarily Spartina alterniflora. At the end of the two-month recovery period, Ischnodemus (Hemiptera: Blissidae) density was over 50% lower in disturbed treatments within both large (terrace) and small (mound) patches. Predatory spider treatment responses were similar to Ischnodemus responses, suggesting a trophic relationship between those two arthropod groups. Alternatively, spiders may have been directly affected by the loss of shelter in the disturbed plots. Prokelisia (Homoptera: Delphacidae), which are generally more mobile than Ischnodemus, were not affected by disturbance treatment or by patch size, suggesting the potential for rapid recolonization following disturbance. Larval stem borers decreased by an order of magnitude in disturbed plots, but only in the large patches. In general, the disturbance effects of vegetation removal on arthropod density and community composition were stronger than patch size effects, and there were few interactions between pulsed disturbance and patch size. Rather, emergent marsh arthropod responses to disturbance and habitat area treatments were linked to the dispersal potential and mobility of each individual taxon.

Timing of disturbance affects biomass and flowering of a saltmarsh plant and attack by stem‐boring herbivores

“…Natural disturbances can interact with the mobility or phenology of consumers to affect the abundance of consumers (Armitage et al. ). By killing plant stems, wrack disturbance killed any stem borers present at the time of the disturbance.…”

“…We focused on stem‐boring herbivores in this manuscript because their presence and abundance over an extended period can be easily quantified by a one‐time collection, and because their intimate associate with plant stems makes them likely to be affected by disturbances that harm plants (Armitage et al. ).…”

Ground-Dwelling Arthropod Community Responses to Recent and Repeated Wildfires in Conifer Forests of Northern New Mexico, USA

“…Ground-dwelling arthropod communities represent a substantial proportion of biodiversity in forest ecosystems [11]. These communities have been reported to be sensitive to alterations in vegetation and litter cover from various forest disturbances, ranging from severe wildfires to relatively minor manipulations of coarse woody debris [12][13][14][15][16][17][18][19][20][21]. Thus, fires may affect ground-dwelling arthropods through direct mortality and/or via impacts on soil and litter/duff layers, understory and overstory vegetation composition, the quantity and arrangement of woody debris, and changes in microclimate [12,[22][23][24][25].…”

“…Of these factors, disturbances have been reported to increase the relative influence of stochastic processes in the short-term, with an increase in deterministic processes over time following disturbance [13,43,45]. Within ground-dwelling arthropods, evidence indicates that dominant assembly processes can vary among different assemblages of the larger community [13], as well as across species with different ecological strategies, relative abundances, and dispersal rates [17,18,39,41,42,[46][47][48].…”

Efficacy of Low and High Complexity Vegetation Treatments for Reestablishing Terrestrial Arthropod Assemblages during Montane Wetland Restoration

“…Restoration inherently alters the meso-landscape, and the nature of these changes to landscape configuration may have important influences on faunal reassembly. Habitat heterogeneity (compositional differences among patches) and complexity (density of structural components) shape invertebrate assemblage structure (Stoner & Lewis 1985;Wiens 1995) and may be especially important during restoration (Palmer et al 1997;Armitage et al 2013). Increasing connectivity (Wiens 1995) with source habitat via reduced patch boundary contrast (Holmquist 1998;Collinge & Palmer 2002) or provision of corridors (Dixon 2009;Eggers et al 2009) might be expected to promote recolonization of restored habitats (Knop et al 2011).…”