Louise Amy Ashton

Globally, deadwood contains approximately 72 Pg of carbon (C), with around 10.9 Pg C released to the atmosphere annually by decomposers1. This recycling of woody biomass is a crucial source of nutrients underpinning primary productivity in forest systems2, with the long-standing consensus that decay rates are predominantly driven by macroclimate8. However, recent studies suggest that biotic factors such as the composition of local tree or soil communities may play a more important role3–7. In a decomposition experiment across five major forest types in Europe, from the Mediterranean to Boreal forest biome, we show that around 80% of variation in deadwood decay rates occurred within rather than between forest types, and that saprotrophic fungi, protist, and nematode communities explained the highest proportion of variability in deadwood mass loss. Local-scale soil abiotic properties, including soil temperature, were the poorest predictors of decay. These results provide evidence that across a continental gradient, climate is not the dominant predictor of deadwood decay, and that the role of soil biota for rates of decomposition extends beyond the activity of the primary decomposers. Our findings challenge the classical paradigm of climatic control over decomposition by predicting that biotic factors primarily mediate deadwood decay, which are dependent on interactions in the soil microbial food web. Our new insights are pivotal for forecasting terrestrial recycling processes and in highlighting the importance of protecting soil biodiversity, as we show that decomposition strongly depends on the composition and structure of the soil biotic community.

Tropical forests harbour a large proportion of Earth’s insect biodiversity. Tropical forest structure produces layers of habitat from the cooler, wetter understorey to the hotter, drier canopy, which provide stratified resources for inhabitants. This gradient of biotic and abiotic factors results in vertically stratified insect communities, often with different assemblages in the understorey and canopy. Vertical distributions of insect taxa are shaped by their niche requirements, with narrower vertical ranges for species with more specialised life history strategies and abiotic requirements. Many studies of vertical stratification focus on single taxonomic orders, often overlooking less well-worked orders, such as Hemiptera, and comparisons of the responses of different taxa sampled at the same time under the same conditions are rare. Here we examine light-trapped samples of adult Lepidoptera (moths), Hemiptera: Auchenorrhyncha (leafhoppers and relatives) and Coleoptera (beetles) collected at 0 m, 10 m, 20 m and 30 m from the ground within a primary tropical forest in Daintree, Queensland, Australia. We found different assemblages of insects in the canopy (20–30 m above ground) and in the understorey (0–10 m) for moths and beetles, but not for Auchenorrhynchs. Species diversity of moths was higher in the canopy than in the understorey, while beetles showed the opposite pattern. In contrast, Auchenorrhyncha did not vary in species diversity between the canopy and the understorey. This may be because the resources used by moths are mostly higher in the canopy and vice versa for beetles. Auchenorrhycha are sap-sucking insects so, provided their host plants can be found throughout the vertical gradient, they might not face the resource availability pressure that drives stratification in moths and beetles. We suggest that future studies of vertical stratification in multiple taxa need to test for such drivers of diversity.

Artificial light at night (ALAN) is a growing threat to biodiversity and ecosystems globally. However, a limited number of studies have focused on the effect of ALAN in the tropical or subtropical regions, and the impact of ALAN on species interactions and ecological processes is particularly understudied. We introduced ALAN into light-naïve forest plots to examine whether ALAN affects herbivory rate and alters the growth and abundance of Nephila pilipes , a common orb-weaver spider. We found illuminated plots had a higher herbivory rate than control plots in the early wet season. The growth rate and abundance of the spider species, however, were not affected by ALAN. Our results indicate that ecological processes in tropical ecosystems, such as herbivory, are potentially sensitive to ALAN. Additionally, this study highlights the importance of a more mechanistic understanding of the sensitivities of tropical species interactions to ALAN and the possible complications caused by environmental variation.

There is ongoing debate about the vulnerability of arthropods to climate change^1,2. Long-term impacts of climate change on arthropod communities could manifest through short-term weather patterns³. Arthropods in the tropics are hyper-diverse^4,5 and contribute many crucial ecosystem functions^6,7, but are comparatively less studied than in temperate regions^1,8,9. Tropical forest arthropods and the functions that they provide may be vulnerable to intensified El Niño events under climate change^10,11,12. Here we perform time-series analysis of data from primary tropical forests, which reveal long-term declines in arthropod diversity and function that were linked to El Niño occurrence. In the Americas, species losses correlated with El Niño sensitivity, and abundant species fluctuated according to feeding traits and level of ecological specialization. Parallel declines in butterflies in Southeast Asia suggested that impacts spanned continents. Predicted arthropod diversity changes correlated with observed rates of invertebrate-mediated decomposition and leaf herbivory, which were oscillating and crashing, respectively, across the tropics. Our analyses suggest that an intensified El Niño immediately threatens tropical forest arthropods and the ecosystem functions that they provide. The broader consequences remain unknown, but such widespread changes could fundamentally alter tropical forest ecosystems¹³. Long-term monitoring of arthropod diversity and forest functioning across the tropics is paramount, as is researching the potential mechanisms that underly this novel threat.

Elevational gradients are widely studied to understand environmental variability and species distribution. Ants play vital roles in ecosystems and are frequently included in elevational biogeography studies. Despite their ecological importance and well-documented elevational patterns, little is known about their temporal variability across elevations. We surveyed ground and arboreal ants in austral summer, autumn, spring, and winter in a subtropical rainforest of Lamington National Park, Queensland, Australia. Given their physiological and microhabitat differences, ground and arboreal ants may exhibit distinct spatiotemporal patterns. Using litter extraction for ground ants and bark spraying for arboreal ants, we collected 14,916 individuals from 124 species. Species richness and abundance were lowest in austral winter, particularly for arboreal ants. Both richness and abundance declined with elevation, and this pattern remained consistent across seasons. While seasonal and elevational differences significantly influenced species composition, seasonal variation did not cause major shifts in the elevational distribution of ground or arboreal ants. A total of 43 species were identified as indicators of specific elevations, with species such as Notoncus capitatus and Colobostruma biconvexa being specialists of low elevations, and undescribed Monomorium and Discothyrea species being specialists of high elevations. In contrast, only two species were identified as seasonal indicators, which were undescribed Tapinoma and Anonychomyrma species, specialists of the warm season. Our findings suggest that ants reduce activity in winter but maintain stable elevational distributions regardless of season or microhabitat use, making their distributions a reliable indicator of their climatic niches.

The interactions between plants and insect herbivores play crucial roles in ecosystem functions and services. Ongoing climate change can affect these interactions through different mechanisms either directly or indirectly. In this review, we outline key ecological traits through which organisms respond to climate change. These include morphology, physiology, and chemistry for plants, and morphology, physiology, and behaviour for insects. We highlight how the responses of those traits to a changing climate might consequently affect herbivory. We propose key ecological questions that need to be addressed for each perspective of plant and insect traits, and we suggest novel approaches for answering these questions. Looking forwards, we outline fruitful areas for exploration of the ecological mechanisms underlying how plant–insect herbivore interactions might respond to climate changes from trait-based approaches.

The conservation status of invertebrates globally is uncertain1–5. In particular, information from primary tropical forests is limited3–5, and yet invertebrates are responsible for crucial processes in the ecosystem6,7 as well as being an essential food source for many vertebrates. There is currently significant debate as to whether invertebrate biodiversity is in long-term decline due to climate change4,8 or changing naturally alongside weather9,10. We demonstrate that both are true in primary tropical forests: intensified El Niño Southern Oscillation cycles under climate change11 are disrupting natural fluctuations in invertebrate diversity. We generalized species richness shifts for nine invertebrate Orders from 33 time series spanning primary forests in the Americas, Africa and Asia. The most speciose Orders were all in long-term decline, while others showed more violent fluctuations in diversity with ENSO extremes over time. El Niño appeared to drive strongest declines in those Orders which naturally increase in diversity during La Niña. In addition, we found our diversity generalizations correlated with tropical-scale reductions in rates of invertebrate driven leaf litter decomposition during El Niño events and steep leaf herbivory declines across 76 decomposition/herbivory studies. Our analyses suggest that increasingly fluctuating climate extremes immediately threaten primary forest invertebrates, their ecological functions and hence the survival of these forests. Understanding the mechanisms behind this novel threat is paramount, as is expanding future long-term monitoring of tropical invertebrate biodiversity.

Circadian rhythms are highly conserved across the tree of life, with light serving as the primary cue for the circadian timer. Photoperiod variation follows a latitudinal gradient, reflecting fluctuations in seasonality that increases towards the poles. As photoperiod variability intensifies at higher latitudes, organisms must develop mechanisms to maintain circadian timing during prolonged periods of light or darkness. Consequently, latitudinal gradients in photic sensitivity occur, as populations in northern latitudes have physiologically adapted to significant seasonal variations in day length. However, the rise of urbanization has introduced artificial light on a global scale, creating new photoperiods for organisms to navigate. This artificial extension of the natural photoperiod is now interacting with evolutionarily established circadian rhythms. Because photic sensitivity follows a latitudinal gradient, this may also inform biogeographic patterns of vulnerability to light pollution. We introduce the term "circadian histories" to describe an organism's evolutionary history of circadian entrainment, which may influence its response to novel light pollution.