Aboveground and belowground arthropods experience different relative influences of stochastic versus deterministic community assembly processes following disturbance

Abstract

BackgroundUnderstanding patterns of biodiversity is a longstanding challenge in ecology. Similar to other biotic groups, arthropod community structure can be shaped by deterministic and stochastic processes, with limited understanding of what moderates the relative influence of these processes. Disturbances have been noted to alter the relative influence of deterministic and stochastic processes on community assembly in various study systems, implicating ecological disturbances as a potential moderator of these forces.MethodsUsing a disturbance gradient along a 5-year chronosequence of insect-induced tree mortality in a subalpine forest of the southern Rocky Mountains, Colorado, USA, we examined changes in community structure and relative influences of deterministic and stochastic processes in the assembly of aboveground (surface and litter-active species) and belowground (species active in organic and mineral soil layers) arthropod communities. Arthropods were sampled for all years of the chronosequence via pitfall traps (aboveground community) and modified Winkler funnels (belowground community) and sorted to morphospecies. Community structure of both communities were assessed via comparisons of morphospecies abundance, diversity, and composition. Assembly processes were inferred from a mixture of linear models and matrix correlations testing for community associations with environmental properties, and from null-deviation models comparing observed vs. expected levels of species turnover (Beta diversity) among samples.ResultsTree mortality altered community structure in both aboveground and belowground arthropod communities, but null models suggested that aboveground communities experienced greater relative influences of deterministic processes, while the relative influence of stochastic processes increased for belowground communities. Additionally, Mantel tests and linear regression models revealed significant associations between the aboveground arthropod communities and vegetation and soil properties, but no significant association among belowground arthropod communities and environmental factors.DiscussionOur results suggest context-dependent influences of stochastic and deterministic community assembly processes across different fractions of a spatially co-occurring ground-dwelling arthropod community following disturbance. This variation in assembly may be linked to contrasting ecological strategies and dispersal rates within above- and below-ground communities. Our findings add to a growing body of evidence indicating concurrent influences of stochastic and deterministic processes in community assembly, and highlight the need to consider potential variation across different fractions of biotic communities when testing community ecology theory and considering conservation strategies.

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

“…Despite the potential for stochastic assembly processes to shape arthropod communities particularly after disturbances [13], the dispersal and probability of colonization by non-pest arthropods at the landscape-scale in forest ecosystems remains poorly studied [13,84,85]. If the stochastic processes related to the probability of local extinction or to the probability of dispersal and recolonization from source populations following disturbances strongly influence the taxa in this system, a dampening in the niche-based associations in these communities should be noted following fire.…”

“…Specifically, we assessed the influence of post-fire understory characteristics on arthropod abundance, taxon diversity, community structure, and the processes governing the assembly of arthropod communities from samples collected in sites of northern New Mexico's Jemez Mountains burned by the 66.8 km 2 Dome Fire in 1996, by the 190 km 2 Cerro Grande Fire in 2000, and in areas of these prior wildfires that were burned again in 2011 by the 630 km 2 Las Conchas Fire. Previous work in conifer forests has revealed an increased influence of stochastic assembly processes in ground-dwelling communities shortly after disturbance, with a shift toward a stronger role of deterministic processes over time [13,45]. Thus, we predicted that ground-dwelling arthropod communities within areas burned by the Las Conchas Fire, five years prior to sampling, would be characterized by a greater relative influence of stochastic processes compared to communities from areas burned ≥16 years prior to our study by the Dome and Cerro Grande Fires.…”

“…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].…”

“…At the same time, stochastic processes linked to the probability of dispersal, colonization, and local extinction can also be key drivers of community structure [33][34][35][36][37]. More recently, simultaneous influences of deterministic and stochastic processes in the assembly of biotic communities, including numerous arthropod assemblages, have been reported (e.g., [13,[38][39][40][41][42][43]).…”

“…Numerous factors are hypothesized to determine the relative influence of deterministic and stochastic assembly processes in biotic communities-e.g., ecosystem productivity, regional biodiversity and dispersal rates, habitat connectivity, species' interactions, and disturbances [40,43,44]. 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].…”