Distance–decay patterns differ between canopy and ground ant assemblages in a tropical rainforest

Abstract

Both decreases in compositional similarity with increasing geographic distances between sites (i.e. distance–decay relationship) and vertical stratification of species composition are key issues in ecology. However, the intersection between these two trends has scarcely been investigated. Here we use identical sampling methods in the canopy and at ground level in a tropical rainforest remnant on the coast of the Gulf of Mexico to evaluate, for the first time, a distance–decay relationship within vertical strata in insect assemblages. We found that the ant assemblage was vertically stratified; ant species richness was higher at ground level than in the canopy, and the species composition differed between the two vertical strata. Moreover, we observed that β-diversity increased with geographic distance at ground level, but not in the canopy strata. However, contrary to our prediction, there was less species turnover (lower β-diversity) between vertical strata than between trees. These findings may reflect differences in the dispersal capacity and nest habit of ants from each vertical stratum, and also habitat heterogeneity on the horizontal scale, e.g. the species of sampled trees. Our results illustrate the importance of sampling more than one vertical stratum to understand the spatial distribution patterns of biological diversity in tropical rainforests.

Species assemblage turnover is greater horizontally than vertically in a complex habitat

“…Hence, we can expect distinct ant communities to be hosted by different individual trees and that the distance between trees per se might not be driving assemblage dissimilarity. The lack of distance effects on high horizontal turnover arboreal ants in our study is consistent with that found in canopy ant assemblages across greater horizontal distances (100-700 m) in rain forest of Mexico, whereas a distance-decay pattern was observed in ground ant assemblages (Antoniazzi et al 2021). For social insects like ants where workers are wingless, vertical movement of workers within the colony tree can be less challenging than movement between trees, especially without vegetation connections such as lianas Foster 2016, Adams et al 2019), which may be lessened in Asian versus American tropics (Dial et al 2004a).…”

“…For amphibians in Madagascar, distance-decay was only found in the canopy and understory but not on the ground, which may be explained by limited habitat connectivity in the canopy (Basham et al 2018). Conversely, distance-decay has been detected only in ground assemblages but not in canopy assemblages for ants in secondary forest in Mexico, which may relate to the higher dispersal capacity and larger territories of canopy ants, as well as higher microhabitat heterogeneity at ground level (Antoniazzi et al 2021). How beta diversity of rain forest fauna changes at comparable horizontal and vertical distances remains largely unknown (Dial et al 2004a, Nakamura et al 2017, partly due to the technical challenges in conducting sampling across replicated horizontal positions for a range of vertical heights (Dial et al 2004a).…”

“…In addition, the interaction between resource availability and connectivity can also influence the importance of competition in driving species turnover (Matthiessen et al 2010, Parr andGibb 2010). Of the few studies considering variation in composition in both horizontal and vertical dimensions in tropical rain forest, patterns documented are idiosyncratic and tend to be taxon-dependent (Basham et al 2018, Antoniazzi et al 2021. The relevant scale when investigating spatial patterns of beta diversity can be dependent on the behavioural, morphological and physiological traits of the study organism and the variation in the habitat (Soininen et al 2018).…”

Species turnover in ant assemblages is greater horizontally than vertically in the world's tallest tropical forest

“…Those studies that do consider community composition both horizontally and vertically in tropical rainforests, find patterns that are idiosyncratic and taxon‐dependent (Antoniazzi et al, 2021 ; Basham et al, 2018 ). The relevant scale of turnover can depend on behavioral, morphological, and physiological traits of organisms interacting with habitat variability (Soininen et al, 2018 ).…”

Canopy Exchange and Modification of Nitrogen Fluxes in Forest Ecosystems

“…Mineralization and nitrification in canopy soils of a tropical montane forest in Ecuador were limited by nitrogen availability, suggesting that increases in nitrogen deposition can enhance nutrient cycling occurring in tree canopies [220]. Last, but not least, soils in tree canopies and in the forest floor are interconnected thanks to leaching of nutrients through throughfall and stemflow [223••, 226], but also via invertebrate species [227][228][229]. As suggested by Van Stan et al [230••], throughfall can be seen like a 'hydrological highway' connecting the atmosphere to the soil, thus, allowing inorganic and organic nitrogen and biological materials (derived from plants, epiphytes and/or microbes) to be transferred to the soil.…”