Insect abundance patterns on vertebrate remains reveal carrion resource quality variation

Vulture Exclusion Halves Large Carcass Decomposition Rates and Doubles Fly Abundance

Carcass consumption by scavengers plays a critical role in wildlife and human health by providing services that maintain ecosystem functioning and potentially mitigate disease spreading. Vultures are particularly efficient scavengers, but their populations have sharply declined in Europe, Asia and Africa, raising concerns about similar declines in the comparatively less studied species of the Americas. While the effects of vulture absence on other vertebrate scavengers have been examined, the impact on invertebrate scavengers and their role in carrion decomposition remains unexplored. To determine the effects of vulture decline, specifically neotropical cathartid vultures, we experimentally excluded this functional group from domestic pig carcasses (Sus scrofa) in Costa Rica, under different habitat conditions (grassland and forest) and across seasons with the aim to assess the impact of vulture exclusion on carrion decomposition and insect abundance. Vulture exclusion halved carcass decomposition rates relative to control carcasses without exclusion. Accordingly, vulture abundance at control carcasses was positively correlated with carcass decomposition rate. Vulture exclusion doubled fly abundance at carcasses relative to controls but did not significantly impact dung beetle abundance at carcasses. These findings suggest that neotropical vultures are instrumental in rapid carrion decomposition, a service that invertebrates alone cannot fully compensate for, underscoring the potential ecological and public health risks associated with neotropical vulture declines and increased flies at carrion sites. Further research is needed to understand the broader implications of vulture loss on ecosystem services and zoonotic disease transmission in the Neotropics.

Effect of insect exclusion and microbial perturbation on piglet mass loss and total body score

Recent conceptual and empirical developments in decomposition research have highlighted the intricate dynamics within necrobiome communities and the roles of various decay drivers. Yet the interactions between these factors and their regulatory mechanisms remain relatively unexplored. A comprehensive understanding of this facet of decomposition science is important, given its broad applicability across ecological and forensic disciplines, and current lack of research which investigates the inter-dependencies between two critical components of the necrobiome (the microbiome and insect activity), and the consequences of this interdependency on mass loss and total body score. Here we investigated the relationships among these key aspects of the decay process. We experimentally manipulated these variables by physically excluding insects and chemically perturbing the external microbiome of piglet (Sus scrofa) carcasses and quantified the effects on mass loss and total body score, as well as insect pre-appearance interval and colonisation. We found that piglets in the insect excluded and microbially perturbed treatment groups exhibited a significant delay in reaching 50 + % of mass loss compared with control piglets with insect access and intact microbiome. However, only remains with insects excluded displayed a significantly slower rate of total mass loss throughout the majority of the experiment and remained a significantly higher mass at the endpoint of 11,000 accumulative degree hours. Additionally, all insect excluded and microbially perturbed treatment groups displayed significantly lower total body scores compared to control piglets at corresponding time points. We also observed a significant delay in insect pre-appearance interval and colonisation for piglets with perturbed microbiomes compared to control piglets. Our findings demonstrate the significance of interacting components of the necrobiome, and the power of manipulative experiments in revealing causal relationships between biota and decomposition rates. These considerations are paramount for developing accurate post-mortem interval estimations and a comprehensive understanding of ecological processes during decomposition.

The Most Attractive Is Not Always the Preferred: Lessons From Necrophagous Dung Beetle Assemblages in a Region of the Central Amazon

Resource attractiveness and preference is determinant to assess how biodiversity is structured in different ecosystems. Necrophagy is the alternative or complementary dietary habit of dung beetles, but a few studies have focused on evaluating how different carrion types attract different species. The goal of this study was to assess the effect of carrion type on attractiveness and preference of dung beetle taxonomic diversity in a region of Central Amazon. Pitfall traps baited with bovine spleen, chicken liver, and fish (freshwater sardine) were installed. Bait attractiveness was estimated through a sampling design that kept exclusively one food type in the field, while bait preference comprised a sampling design with more than one food type offered simultaneously in a concentrated area. We collected 3151 individuals from 24 dung beetle species. Bovine spleen was the most attractive bait in both food preference and food attractiveness experiments, being the only carrion type in which species demonstrated preference. Each carrion type attracted distinct dung beetle assemblages. This study demonstrates that Amazonian dung beetles prefer specific carrion types, which serves as a basis for future studies related to dung beetle diet.

Behavioral interactions are modulated by facilitation along a heterotrophic succession

Competition and facilitation drive ecological succession but are often hard to quantify. In this sense, behavioral data may be a key tool to analyze interaction networks, providing insights into temporal trends in facilitation and competition processes within animal heterotrophic succession. Here, we perform the first in-depth analysis of the factors driving temporal dynamics of carcass consumption by analyzing behavioral patterns (i.e., interactions) and community dynamics metrics (i.e., species richness, abundance, turnover, and diversity) in a Neotropical scavenger guild. For this purpose, we monitored goat carcasses using automatic cameras. From 573 reviewed videos, we registered 1784 intraspecific and 624 interspecific interactions, using intraspecific and interspecific aggressions (n = 2048) as a behavioral proxy of competition intensity. Our results show that resource availability shapes behavioral interactions between vultures, with a specific effect of the different species on behavioral and competition dynamics, showing the existence of a hierarchy between species. Furthermore, behavioral processes linked to carcass opening tended to be facilitative, related to moments of higher tolerance (i.e., lower aggressiveness), thus reducing competition intensity and also affecting community structure and dynamics. This novel framework demonstrates complex ephemeral successional processes characterized by a fluctuation in facilitation and competition intensity during the consumption of an unpredictable resource linked to key ecosystem processes.

Aggregation in an heterospecific population of blowfly larvae: social behaviour is impacted by species-specific thermal requirements and settlement order

Larvae of several blowfly species grow on carcasses and actively aggregate together. They face harsh developmental conditions resulting in a strong pressure to reduce development time: this is achieved either through thermoregulation or aggregation. We investigate how these two developmental strategies are modulated within heterospecific groups. In a first experiment, larvae of two species with different thermal requirements were deposited simultaneously on a thermal gradient. This resulted in the formation of two monospecific groups, each located at the species-specific thermal preferendum. However, when Calliphora vomitoria (Linnaeus) larvae were placed first, the later arriving Lucilia sericata (Meigen) larvae attracted the whole group to its own thermal preferendum. In the reverse experiment, half of the replicates resulted in single dense heterospecific groups observed at temperatures ranging from C. vomitoria to L. sericata preferendum. The other half of the replicates resulted in loose groups spread out on the thermal gradient. These results highlight the emergence of collective decisions ranging from thermal optimization to heterospecific aggregation at suboptimal temperatures. They demonstrate that species settlement order strongly affects self-organization processes and mixed-species group formation. We conclude that thermal optimization and heterospecific niche construction are two developmental strategies of carrion fly larvae. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

The ephemeral resource patch concept

Ephemeral resource patches (ERPs) - short lived resources including dung, carrion, temporary pools, rotting vegetation, decaying wood, and fungi - are found throughout every ecosystem. Their short-lived dynamics greatly enhance ecosystem heterogeneity and have shaped the evolutionary trajectories of a wide range of organisms - from bacteria to insects and amphibians. Despite this, there has been no attempt to distinguish ERPs clearly from other resource types, to identify their shared spatiotemporal characteristics, or to articulate their broad ecological and evolutionary influences on biotic communities. Here, we define ERPs as any distinct consumable resources which (i) are homogeneous (genetically, chemically, or structurally) relative to the surrounding matrix, (ii) host a discrete multitrophic community consisting of species that cannot replicate solely in any of the surrounding matrix, and (iii) cannot maintain a balance between depletion and renewal, which in turn, prevents multiple generations of consumers/users or reaching a community equilibrium. We outline the wide range of ERPs that fit these criteria, propose 12 spatiotemporal characteristics along which ERPs can vary, and synthesise a large body of literature that relates ERP dynamics to ecological and evolutionary theory. We draw this knowledge together and present a new unifying conceptual framework that incorporates how ERPs have shaped the adaptive trajectories of organisms, the structure of ecosystems, and how they can be integrated into biodiversity management and conservation. Future research should focus on how inter- and intra-resource variation occurs in nature - with a particular focus on resource × environment × genotype interactions. This will likely reveal novel adaptive strategies, aid the development of new eco-evolutionary theory, and greatly improve our understanding of the form and function of organisms and ecosystems.