A highly resolved food web for insect seed predators in a species-rich tropical forest

Tropical–temperate comparisons in insect seed predation vary between study levels and years

The biotic interaction hypothesis, which states the species interaction becomes stronger in the tropics, is deeply rooted in classic ecological literature and widely accepted to contribute to the latitudinal gradients of biodiversity. Tests in latitudinal insect–plant interaction have emphasized leaf‐eating insects on a single or a few plant species rather than within an entire community and mixed accumulating evidence, leaving the biotic interaction hypothesis disputed. We aimed to test the hypothesis by quantifying insect seed predation in a pair of tropical and temperate forest communities with similar elevations. We applied a consistent study design to sample predispersal seeds with systematically set seed traps in 2019–2020 and examined internally feeding insects. The intensity of seed predation was measured and further applied to tropical versus temperate comparison at two levels (cross‐species and community‐wide). Our results showed every latitudinal pattern associated with different study levels and years, that is, negative (greater granivory in the tropics in community‐wide comparison in 2020), positive (less granivory in the tropics in community‐wide and cross‐species comparison in 2019), and missing (similar level of granivory in the tropics in cross‐species comparisons in 2020). The cross‐species level analyses ignore differences among species in seed production and weaken or even lose the latitudinal trend detected by community‐wide comparisons. The between‐year discrepancy in tropical–temperate comparisons relates to the highly variable annual seed composition in the temperate forest due to mast seeding of dominant species. Our study highlights that long‐term community‐level researches across biomes are essential to assess the latitudinal biotic interaction hypothesis.

Genomics-based higher classification of the species-rich Hairstreaks (Lepidoptera: Lycaenidae: Eumaeini)

We propose a higher classification of the lycaenid hairstreak tribe Eumaeini - one of the youngest and most species-rich butterfly tribes - based on autosome, Lepidopteran Z sex chromosome, and mitochondrial protein-coding genes. The subtribe Neolycaenina Korb is a synonym of Callophryidina Tutt, and subtribe Tmolusina Bálint is a synonym of Strephonotina K. Johnson, Austin, Le Crom, & Salazar. Proposed names are Rhammina Prieto & Busby, new subtribe; Timaetina Busby & Prieto, new subtribe; Atlidina Martins & Duarte, new subtribe; Evenina Faynel & Grishin, new subtribe; Jantheclina Robbins & Faynel, new subtribe; Paiwarriina Lamas & Robbins, new subtribe; Cupatheclina Lamas & Grishin, new subtribe; Parrhasiina Busby & Robbins, new subtribe; Ipideclina Martins & Grishin, new subtribe; and Trichonidina Duarte & Faynel, new subtribe. Phylogenetic results from the autosome and Z sex chromosome analyses are similar. Future analyses of datasets with hundreds of terminal taxa may be more practical time-wise by focussing on the smaller number of sex chromosome sequences (2.6% of nuclear protein-coding sequences). The phylogenetic classification and biological summaries for each subtribe suggest that a variety of factors affected Eumaeini diversification. About a dozen kinds of male secondary sexual organs with frequent evolutionary gains and losses occur in Atlidina, Evenina, and Jantheclina (141 species combined). Females have been shown to use these organs to discriminate between conspecific and non-conspecific males, facilitating sympatry among close relatives. Eumaeina, Rhammina, and Timaetina (140 species combined) are overwhelmingly montane with some evidence for a higher incidence of sympatric diversification. Seven Neotropical lineages in five subtribes invaded the temperate parts of the Nearctic Region with a diversification increase in the Callophryidina (262 species). North American Satyrium and Callophrys then invaded the Palearctic at least once each, with a major species-richness increase in Satyrium. The evolution of litter feeding detritivores within Calycopidina (172 species) resulted in an increase in diversification rate compared with its flower-feeding sister lineage. Atlidina, Strephonotina, Parrhasiina, and Strymonina (562 species combined) each contain a mixture of genera that specialize on one or two caterpillar food plant families and genera that are polyphagous. These would be appropriate subtribes to assess how the breadth of caterpillar food plants and the frequency of host shifts affected diversification.

A remarkable legion of guests: Diversity and host specificity of army ant symbionts

Tropical rainforests are among the most diverse biomes on Earth. While species inventories are far from complete for any tropical rainforest, even less is known about the intricate species interactions that form the basis of these ecological communities. One fascinating but poorly studied example are the symbiotic associations between army ants and their rich assemblages of parasitic arthropod guests. Hundreds of these guests, or myrmecophiles, have been taxonomically described. However, because previous work has mainly been based on haphazard collections from disjunct populations, it remains challenging to define species boundaries. We therefore know little about the species richness, abundance and host specificity of most guests in any given population, which is crucial to understand co-evolutionary and ecological dynamics. Here, we report a quantitative community survey of myrmecophiles parasitizing the six sympatric Eciton army ant species in a Costa Rican rainforest. Combining DNA barcoding with morphological identification of over 2,000 specimens, we discovered 62 species, including 49 beetles, 11 flies, one millipede and one silverfish. At least 14 of these species were new to science. Ecological network analysis revealed a clear signal of host partitioning, and each Eciton species was host to both specialists and generalists. These varying degrees in host specificities translated into a moderate level of network specificity, highlighting the system's level of biotic pluralism in terms of biodiversity and interaction diversity. By providing vouchered DNA barcodes for army ant guest species, this study provides a baseline for future work on co-evolutionary and ecological dynamics in these species-rich host-symbiont networks across the Neotropical realm.

Seed tannin composition of tropical plants

Seeds collected from trees, shrubs and lianas growing on Barro Colorado Island, Panama, were analyzed for their content of phenolic compounds, oxidative activities and protein precipitation capacities. Proanthocyanidins and hydrolysable tannins were detected in one-third of 189 studied species. The most oxidatively active group of species were the ones containing prodelphinidins and ellagitannins whereas the species that had the highest protein precipitation capacity in relation to their total phenolics were the ones containing punicalagin. In addition, the oxidative activity and relative protein precipitation capacity were exceptionally high in the proanthocyanidin-rich genus Psychotria. This study offers a comprehensive overview on the tannin composition and the alkaline oxidative activities and protein precipitation capacities of the seeds of tropical plants.

Ecophylogenetics redux

Species' evolutionary histories shape their present-day ecologies, but the integration of phylogenetic approaches in ecology has had a contentious history. The field of ecophylogenetics promised to reveal the process of community assembly from simple indices of phylogenetic pairwise distances - communities shaped by environmental filtering were composed of closely related species, whereas communities shaped by competition were composed of less closely related species. However, the mapping of ecology onto phylogeny proved to be not so straightforward, and the field remains mired in controversy. Nonetheless, ecophylogenetic methods provided important advances across ecology. For example the phylogenetic distances between species is a strong predictor of pest and pathogen sharing, and can thus inform models of species invasion, coexistence and the disease dilution/amplification effect of biodiversity. The phylogenetic structure of communities may also provide information on niche space occupancy, helping interpret patterns of facilitation, succession and ecosystem functioning - with relevance for conservation and restoration - and the dynamics among species within foodwebs and metacommunities. I suggest leveraging advances in our understanding of the process of evolution on phylogenetic trees would allow the field to progress further, while maintaining the essence of the original vision that proved so seductive.

Seed predation selects for reproductive variability and synchrony in perennial plants

Annually variable and synchronous seed production by plant populations, or masting, is a widespread reproductive strategy in long-lived plants. Masting is thought to be selectively beneficial because interannual variability and synchrony increase the fitness of plants through economies of scale that decrease the cost of reproduction per surviving offspring. Predator satiation is believed to be a key economy of scale, but whether it can drive phenotypic evolution for masting in plants has been rarely explored. We used data from seven plant species (Quercus humilis, Quercus ilex, Quercus rubra, Quercus alba, Quercus montana, Sorbus aucuparia and Pinus pinea) to determine whether predispersal seed predation selects for plant phenotypes that mast. Predation selected for interannual variability in Mediterranean oaks (Q. humilis and Q. ilex), for synchrony in Q. rubra, and for both interannual variability and reproductive synchrony in S. aucuparia and P. pinea. Predation never selected for negative temporal autocorrelation of seed production. Predation by invertebrates appears to select for only some aspects of masting, most importantly high coefficient of variation, supporting individual-level benefits of the population-level phenomenon of mast seeding. Determining the selective benefits of masting is complex because of interactions with other seed predators, which may impose contradictory selective pressures.

When do Janzen-Connell effects matter? A phylogenetic meta-analysis of conspecific negative distance and density dependence experiments

The Janzen-Connell (J-C) hypothesis suggests that specialised natural enemies cause distance- or density-dependent mortality among host plants and is regarded as an important mechanism for species coexistence. However, there remains debate about whether this phenomenon is widespread and how variation is structured across taxa and life stages. We performed the largest meta-analysis of experimental studies conducted under natural settings to date. We found little evidence of distance-dependent or density-dependent mortality when grouping all types of manipulations. Our analysis also reveals very large variation in response among species, with 38.5% of species even showing positive responses to manipulations. However, we found a strong signal of distance-dependent mortality among seedlings but not seed experiments, which we attribute to (a) seedlings sharing susceptible tissues with adults (leaves, wood, roots), (b) seedling enemies having worse dispersal than seed enemies and (c) seedlings having fewer physical and chemical defences than seeds. Both density- and distance-dependent mortality showed large variation within genera and families, suggesting that J-C effects are not strongly phylogenetically conserved. There were no clear trends with latitude, rainfall or study duration. We conclude that J-C effects may not be as pervasive as widely thought. Understanding the variation in J-C effects provides opportunities for new discoveries that will refine our understanding of J-C effects and its role in species coexistence.

One side makes you taller: a mushroom–eating butterfly caterpillar (Lycaenidae) in Costa Rica

Electrostrymon denarius is the first mushroom-feeding butterfly caterpillar discovered in the New World. It belongs to the Calycopidina, a subtribe of lycaenid butterflies whose caterpillars eat detritus and seeds in the leaf litter. Electrostrymon denarius has not been reared previously, and we illustrate and briefly describe the biology and morphology of its caterpillar and pupa. The significance of this discovery is that it increases the range of organic leaf litter substrates that Calycopidina caterpillars will eat. Increased diet breadth may decrease the likelihood of species extinction.

Is Variation in Conspecific Negative Density Dependence Driving Tree Diversity Patterns at Large Scales?

Half a century ago, Janzen and Connell hypothesized that the high tree species diversity in tropical forests is maintained by specialized natural enemies. Along with other mechanisms, these can cause conspecific negative density dependence (CNDD) and thus maintain species diversity. Numerous studies have measured proxies of CNDD worldwide, but doubt about its relative importance remains. We find ample evidence for CNDD in local populations, but methodological limitations make it difficult to assess if CNDD scales up to control community diversity and thereby local and global biodiversity patterns. A combination of more robust statistical methods, new study designs, and eco-evolutionary models are needed to provide a more definite evaluation of the importance of CNDD for geographic variation in plant species diversity.

A global class reunion with multiple groups feasting on the declining insect smorgasbord

We report a detection of a surprising similarity in the diet of predators across distant phyla. Though just a first glimpse into the subject, our discovery contradicts traditional aspects of biology, as the earliest notions in ecology have linked the most severe competition of resources with evolutionary relatedness. We argue that our finding deserves more research, and propose a plan to reveal more information on the current biodiversity loss around the world. While doing so, we expand the recently proposed conservation roadmaps into a parallel study of global interaction networks.

Quantifying the relative importance of variation in predation and the environment for species coexistence

Coexistence and food web theory are two cornerstones of the long-standing effort to understand how species coexist. Although competition and predation are known to act simultaneously in communities, theory and empirical study of these processes continue to be developed largely independently. Here, we integrate modern coexistence theory and food web theory to simultaneously quantify the relative importance of predation and environmental fluctuations for species coexistence. We first examine coexistence in a theoretical, multitrophic model, adding complexity to the food web using machine learning approaches. We then apply our framework to a stochastic model of the rocky intertidal food web, partitioning empirical coexistence dynamics. We find the main effects of both environmental fluctuations and variation in predator abundances contribute substantially to species coexistence. Unexpectedly, their interaction tends to destabilise coexistence, leading to new insights about the role of bottom-up vs. top-down forces in both theory and the rocky intertidal ecosystem.