Coevolutionary models suggest that herbivores drive diversification and community composition in plants. For herbivores, many questions remain regarding how plant defenses shape host choice and ...community structure. We addressed these questions using the tree genus Inga and its lepidopteran herbivores in the Amazon. We constructed phylogenies for both plants and insects and quantified host associations and plant defenses. We found that similarity in herbivore assemblages between Inga species was correlated with similarity in defenses. There was no correlation with phylogeny, a result consistent with our observations that the expression of defenses in Inga is independent of phylogeny. Furthermore, host defensive traits explained 40% of herbivore community similarity. Analyses at finer taxonomic scales showed that different lepidopteran clades select hosts based on different defenses, suggesting taxon-specific histories of herbivore–host plant interactions. Finally, we compared the phylogeny and defenses of Inga to phylogenies for the major lepidopteran clades. We found that closely related herbivores fed on Inga with similar defenses rather than on closely related plants. Together, these results suggest that plant defenses might be more evolutionarily labile than the herbivore traits related to host association. Hence, there is an apparent asymmetry in the evolutionary interactions between Inga and its herbivores. Although plants may evolve under selection by herbivores, we hypothesize that herbivores may not show coevolutionary adaptations, but instead “chase” hosts based on the herbivore’s own traits at the time that they encounter a new host, a pattern more consistent with resource tracking than with the arms race model of coevolution.
Tropical forests sustain many ant species whose mating events often involve conspicuous flying swarms of winged gynes and males. The success of these reproductive flights depends on environmental ...variables and determines the maintenance of local ant diversity. However, we lack a strong understanding of the role of environmental variables in shaping the phenology of these flights. Using a combination of community-level analyses and a time-series model on male abundance, we studied male ant phenology in a seasonally wet lowland rainforest in the Panama Canal. The male flights of 161 ant species, sampled with 10 Malaise traps during 58 consecutive weeks (from August 2014 to September 2015), varied widely in number (mean = 9.8 weeks, median = 4, range = 1 to 58). Those species abundant enough for analysis (n = 97) flew mainly towards the end of the dry season and at the start of the rainy season. While litterfall, rain, temperature, and air humidity explained community composition, the time-series model estimators elucidated more complex patterns of reproductive investment across the entire year. For example, male abundance increased in weeks when maximum daily temperature increased and in wet weeks during the dry season. On the contrary, male abundance decreased in periods when rain receded (e.g., at the start of the dry season), in periods when rain fell daily (e.g., right after the beginning of the wet season), or when there was an increase in the short-term rate of litterfall (e.g., at the end of the dry season). Together, these results suggest that the BCI ant community is adapted to the dry/wet transition as the best timing of reproductive investment. We hypothesize that current climate change scenarios for tropical regions with higher average temperature, but lower rainfall, may generate phenological mismatches between reproductive flights and the adequate conditions needed for a successful start of the colony.
Added Na was used to determine whether litter decomposition and associated fungal biomass and termites are limited by Na availability in a lowland tropical rainforest at Yasuni, Ecuador. This is a ...partial test of the "sodium ecosystem respiration" (SER) hypothesis that posits Na is critical for consumers but not plants, that Na shortfall is more likely on highly weathered soils inland from oceanic aerosols, and that this shortfall results in decreased decomposer activity. We fertilized 4 × 4 m plots twice a month for a year with quantities of Na comparable to those falling on a coastal tropical rainforest. Decomposition rates of four substrates were consistently higher on +NaCl plots by up to 70% for cellulose, and 78%, 68%, and 29% for three woods of increasing percentage lignin. The density of termite workers averaged 17-fold higher on +NaCl plots; fungal biomass failed to differ. After controlling for temperature and precipitation, which co-limit gross primay productivity (GPP) and ecosystem respiration (ER), these results suggest that Na shortfall is an agent enhancing the storage of coarse woody debris in inland tropical forests.
Community ecology seeks to unravel the mechanisms that allow species to coexist in space. Some of the contending mechanisms may generate tractable signatures in the amount of trait and phylogenetic ...dispersion among co‐existing species. When a community presents a pattern with reduced trait or phylogenetic dispersion, mechanisms based on ecological filters are brought into consideration. On the other hand, limiting similarity mechanisms such as competitive exclusion are proposed when communities present patterns of trait or phylogenetic even‐dispersion. The strength of these mechanisms likely varies with the spatial scale of an observed sample. I surveyed species‐rich tropical litter ant communities in a spatially nested design that allowed me to explore the spatial scales, fine (0.25 m²), intermediate (9 m²), and broad (361 m²) at which these mechanisms act. I then assessed the relationship between observed ant communities and potential species pools ranging in size, from plot, site, and island‐wide areas. Patterns of phylogenetic dispersion within ant communities suggested that ant communities were composed of species that were more closely related than expected by a random sampling of phylogenetic pools. The magnitude of phylogenetic ‘clustering’ increased with the size of the species pool but was similar among communities assembled from different spatial scales. Patterns of dispersion of one ecological trait (i.e. body size) within ant communities also showed clustering of body sizes, and most communities were composed of ant species that were smaller than expected by a random sampling of trait pools. Trait clustering increased with the size of the species pool but decreased at broad spatial scales. Together, these results suggest that ecological filters, not interspecific interactions, are structuring tropical ant communities, favoring clades with small worker sizes. The larger dependency on the size of regional pools than on the spatial scale suggests that environmental heterogeneity is greater among than within the study sites.
In tropical forests, herbivorous arthropods remove between 7% up to 48% of leaf area, which has forced plants to evolve defense strategies. These strategies influence the palatability of leaves. ...Palatability, which reflects a syndrome of leaf traits, in turn influences both the abundance and the mean body mass not only of particular arthropod taxa but also of the total communities. In this study, we tested two hypotheses: (H1) The abundance of two important chewer guilds ('leaf chewers' and 'rostrum chewers'), dominant components of arthropod communities, is positively related to the palatability of host trees. (H2) Lower palatability leads to an increased mean body mass of chewers (Jarman-Bell principle). Arthropods were collected by fogging the canopies of 90 tropical trees representing 31 species in three plots at 1000 m and three at 2000 m a.s.l. Palatability was assessed by measuring several 'leaf traits' of each host tree and by conducting a feeding trial with the generalist herbivore Gryllus assimilis (Orthoptera, Gryllidae). Leaf traits provided partial support for H1, as abundance of leaf chewers but not of rostrum chewers was positively affected by the experimentally estimated palatability. There was no support for H2 as neither leaf traits nor experimentally estimated palatability affected the mean body mass of leaf chewers. The mean body mass of rostrum chewers was positively related to palatability. Thus, leaf traits and experimentally estimated palatability influenced the abundance and mean body mass of chewing arthropods on the community level. However, the data were not consistent with the Jarman-Bell principle. Overall, our results suggest that the palatability of leaves is not among the dominant factors influencing abundance and mean body mass of the community of chewing arthropod herbivores. If other factors, such as the microclimate, predation or further (a-)biotic interactions are more important has to be analyzed in refined studies.
Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the ...equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution.
Microhabitat differentiation of species communities such as vertical stratification in tropical forests contributes to species coexistence and thus biodiversity. However, little is known about how ...the extent of stratification changes during forest recovery and influences community reassembly. Environmental filtering determines community reassembly in time (succession) and in space (stratification), hence functional and phylogenetic composition of species communities are highly dynamic. It is poorly understood if and how these two concurrent filters—forest recovery and stratification—interact.
In a tropical forest chronosequence in Ecuador spanning 34 years of natural recovery, we investigated the recovery trajectory of ant communities in three overlapping strata (ground, leaf litter, lower tree trunk) by quantifying 13 traits, as well as the functional and phylogenetic diversity of the ants. We expected that functional and phylogenetic diversity would increase with recovery time and that each ant community within each stratum would show a distinct functional reassembly. We predicted that traits related to ant diet would show divergent trajectories reflecting an increase in niche differentiation with recovery time. On the other hand, traits related to the abiotic environment were predicted to show convergent trajectories due to a more similar microclimate across strata with increasing recovery age.
Most of the functional traits and the phylogenetic diversity of the ants were clearly stratified, confirming previous findings. However, neither functional nor phylogenetic diversity increased with recovery time. Community‐weighted trait means had complex relationships to recovery time and the majority were shaped by a statistical interaction between recovery time and stratum, confirming our expectations. However, most trait trajectories converged among strata with increasing recovery time regardless of whether they were related to ant diet or environmental conditions.
We confirm the hypothesized interaction among environmental filters during the functional reassembly in tropical forests. Communities in individual strata respond differently to recovery, and possible filter mechanisms likely arise from both abiotic (e.g. microclimate) and biotic (e.g. diet) conditions. Since vertical stratification is prevalent across animal and plant taxa, our results highlight the importance of stratum‐specific analysis in dynamic ecosystems and may generalize beyond ants.
This new study explores how stratification and forest recovery influence the functional reassembly of a major faunistic group, the ants. In a recovering forest in Ecuador, the study finds that functional and phylogenetic diversity were relatively stable, while traits were shaped by a complex interplay of stratification and recovery.
Army ants are among the top arthropod predators and considered keystone species in tropical ecosystems. During daily mass raids with many thousand workers, army ants hunt live prey, likely exerting ...strong top‐down control on prey species. Many tropical sites exhibit a high army ant species diversity (>20 species), suggesting that sympatric species partition the available prey niches. However, whether and to what extent this is achieved has not been intensively studied yet. We therefore conducted a large‐scale diet survey of a community of surface‐raiding army ants at La Selva Biological Station in Costa Rica. We systematically collected 3,262 prey items from eleven army ant species (genera Eciton, Nomamyrmex and Neivamyrmex). Prey items were classified as ant prey or non‐ant prey. The prey nearly exclusively consisted of other ants (98%), and most booty was ant brood (87%). Using morphological characters and DNA barcoding, we identified a total of 1,103 ant prey specimens to the species level. One hundred twenty‐nine ant species were detected among the army ant prey, representing about 30% of the known local ant diversity. Using weighted bipartite network analyses, we show that prey specialization in army ants is unexpectedly high and prey niche overlap very small. Besides food niche differentiation, we uncovered a spatiotemporal niche differentiation in army ant raid activity. We discuss competition‐driven multidimensional niche differentiation and predator–prey arms races as possible mechanisms underlying prey specialization in army ants. By combining systematic prey sampling with species‐level prey identification and network analyses, our integrative approach can guide future research by portraying how predator–prey interactions in complex communities can be reliably studied, even in cases where morphological prey identification is infeasible.
Abstract
Tropical forest recovery is fundamental to addressing the intertwined climate and biodiversity loss crises. While regenerating trees sequester carbon relatively quickly, the pace of ...biodiversity recovery remains contentious. Here, we use bioacoustics and metabarcoding to measure forest recovery post-agriculture in a global biodiversity hotspot in Ecuador. We show that the community composition, and not species richness, of vocalizing vertebrates identified by experts reflects the restoration gradient. Two automated measures – an acoustic index model and a bird community composition derived from an independently developed Convolutional Neural Network - correlated well with restoration (adj-R² = 0.62 and 0.69, respectively). Importantly, both measures reflected composition of non-vocalizing nocturnal insects identified via metabarcoding. We show that such automated monitoring tools, based on new technologies, can effectively monitor the success of forest recovery, using robust and reproducible data.
Regrowing secondary forests dominate tropical regions today, and a mechanistic understanding of their recovery dynamics provides important insights for conservation. In particular, land‐use legacy ...effects on the fauna have rarely been investigated. One of the most ecologically dominant and functionally important animal groups in tropical forests are the ants. Here, we investigated the recovery of ant communities in a forest–agricultural habitat mosaic in the Ecuadorian Chocó region. We used a replicated chronosequence of previously used cacao plantations and pastures with 1–34 years of regeneration time to study the recovery dynamics of species communities and functional diversity across the two land‐use legacies. We compared two independent components of responses on these community properties: resistance, which is measured as the proportion of an initial property that remains following the disturbance; and resilience, which is the rate of recovery relative to its loss. We found that compositional and trait structure similarity to old‐growth forest communities increased with regeneration age, whereas ant species richness remained always at a high level along the chronosequence. Land‐use legacies influenced species composition, with former cacao plantations showing higher resemblance to old‐growth forests than former pastures along the chronosequence. While resistance was low for species composition and high for species richness and traits, all community properties had similarly high resilience. In essence, our results show that ant communities of the Chocó recovery rapidly, with former cacao reaching predicted old‐growth forest community levels after 21 years and pastures after 29 years. Recovery in this community was faster than reported from other ecosystems and was likely facilitated by the low‐intensity farming in agricultural sites and their proximity to old‐growth forest remnants. Our study indicates the great recovery potential for this otherwise highly threatened biodiversity hotspot.
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