Secondary succession has surprisingly low impact on arboreal ant communities in tropical montane rainforest

Abstract

Understanding forest regeneration processes is increasingly important as disturbed forests spread rapidly in tropical landscapes. While successional dynamics are relatively well-understood for plants, they remain poorly known for tropical insects, particularly in montane rainforests and tree canopies. We studied the effect of montane forest succession on arboreal ant communities in New Guinea near their natural elevational limit (1800 m a.s.l.). We censused ant species and nests in replicated 0.1-ha plots of primary, old and young secondary forests, destined to be felled for gardens by the local landowners. Overall, 1249 felled trees were dissected for all ant-associated microhabitats. We used rarefaction-based models manipulating vegetation structure and multivariate randomizations to assess the effects of tree density, tree size, and nesting microhabitats on the ant communities. We expected increased ant species diversity, microhabitat specialization, and species turnover among trees throughout the succession, with distinct community composition among the stages. In contrast to our expectations, ant species composition and diversity per plot did not change during succession, and species similarity among trees was significantly higher only in old secondary forest. The number of ant species per tree increased with forest age, but trees of similar size hosted only slightly more species in primary than secondary forests. Many ant species were associated with particular nesting microhabitats; however, the same microhabitat types occurred in all stages and thus did not generate successional trends in ant communities. Secondary succession had an unexpectedly low impact on tree-dwelling ant communities in this montane ecosystem, in contrast with our previous findings from lowland rainforests. These results highlight the need to study successional processes along entire elevational gradients, as montane taxa may react differently to vegetation changes than their lowland counterparts.

Nest microhabitats and tree size mediate shifts in ant community structure across elevation in tropical rainforest canopies

“…Our study has demonstrated that vegetation structure and its differential use by ant species can contribute to the elevational patterns in tree-nesting ant richness, abundance and community structure. We comprehensively sampled all nests in all trees in forest plots, an approach previously used to explore the effects of forest succession, but not a forest elevational gradient (Klimes et al 2012, Mottl et al 2019. We found a strong mid-elevation peak in nest abundance and species richness, and there, in the largest trees species co-occurred more than expected by chance.…”

“…inside myrmecophytic bulb plants such as Hydnophytum and Myrmecodia, or under the roots of mosses, orchids and ferns) as present on the supporting tree. Nests were categorized into 12 types based on nest locations (microhabitat sites), where they were found within each tree: 'on trunk base', 'under epiphyte roots', 'cavity/gallery in trunk', 'carton/soil/silk on leaves', 'under bark', 'on bark', 'in/under liana', 'myrmecophytic epiphyte', 'cavity/ gallery in live branch', 'cavity/gallery in live twig', 'in dead/ rotten branch' and 'in dead/rotten twig' (Klimes et al 2012, Mottl et al 2019. We recorded the distance in metres of the nest from ground level (nest height hereafter), and estimated nest size on an ordinal scale (1: ≤ 100 workers, 2: 100-500 workers, 3: 500-1000 workers 4: > 1000 workers).…”

Spatial covariance of herbivorous and predatory guilds of forest canopy arthropods along a latitudinal gradient

“…This non‐linearity can probably be attributed to the distribution of microhabitats, some of which were found only on large‐canopy trees, or trees with numerous lianas or epiphytes (Klimes, 2017). Indeed, microhabitat richness was found to be the main driver for the pattern in arboreal ant communities in other extensive whole‐forest studies (Klimes et al ., 2015; Mottl et al ., 2019; Plowman et al ., 2019). A similar pattern of tree biomass affecting the abundances of arboreal arthropods has also been observed in specialist herbivores feeding only on a single tree genus or species (Novotny et al ., 2006, 2010).…”

“…Basset et al ., 2012), plot‐based censuses can become a useful tool to assess the abundances of arthropods and improve our understanding of habitat‐ and temporal‐driven changes. For example studies of whole‐forest arthropod communities have already revealed the contrasting effect of forest age on leaf‐chewing communities (Redmond et al ., 2018) and tree‐dwelling ants (Mottl et al ., 2019), suggesting the importance of microhabitats for ants. In the light of recent reports of a worldwide decline in insects (Basset and Lamarre, 2019), the need to understand the processes underpinning arthropod ecology becomes increasingly important.…”

“…For ants, we hand‐collected foraging individuals during a standardised search immediately upon felling, beginning with the base of the trunk and working up to the top of the canopy (Klimes et al ., 2015). In addition, we sampled all ant nests found during the destructive sampling (including cryptic nests inside tree tissues and the attached epiphytes and lianas, see details in Klimes et al ., 2015; Mottl et al ., 2019; Plowman et al ., 2019). The size of nests was visually estimated on a three‐level categorical scale: (1) <100, (2) 100–1000 and (3) >1000 individuals.…”