Unexpectedly diverse forest dung beetle communities in degraded rain forest landscapes in Madagascar

Abstract

Tropical forests, which harbor high levels of biodiversity, are being lost at an alarming speed. Madagascar, a biodiversity hotspot, has lost more than half of its original forest cover. Most of the remaining forests are small fragments of primary and secondary forest with differing degrees of human impact. These forests, as well as coffee and fruit plantations, may be important in supporting the forest‐dependent biodiversity in Madagascar but this has been little studied. In Madagascar, dung beetles, which offer important ecosystem services, are largely restricted to forests. We examined the ability of fragmented and degraded forests to support dung beetle diversity, compared to the large areas of primary forest in eastern Madagascar. We found a general trend of a reduction of species with a loss of forest connectivity. In contrast, a higher level of forest disturbance was associated with higher species diversity. In several sites of low‐quality forest as many or more species were found as in less disturbed and primary forests. The average size of dung beetles was smaller in the lower quality localities than in the primary forests. These findings suggest that many forest dung beetles in Madagascar are better adapted to forest disturbance than earlier expected, although they require some level of connectivity to surrounding forest. Abstract in Malagasy is available with online material.

Recovery of dung beetle biodiversity and traits in a regenerating rainforest: a case study from Costa Rica's Osa Peninsula

“…Whereas contiguous secondary growth and plantation forests showed community compositions similar to that of old growth forests, open and fragmented habitats had degraded and impoverished levels of dung beetle biodiversity. Although Torppa et al (2020) found diverse communities of dung beetles in highly degraded landscapes of Madagascar when closed canopy forest was nearby, we did not, even though our grassland and forest strips were surrounded by contiguous high-quality habitat. Torppa et al (2020) discuss the reduction of mammals in the surrounding forests as a potential contributing factor, whereas at our site in Osa, informal communications with locals and site managers who acquired the property almost 20 years ago, suggest that many mammal species that were absent, like tapir, puma and white-lipped peccary, have now returned (confirmed by the use of camera trap surveys at the site).…”

“…Although Torppa et al . (2020) found diverse communities of dung beetles in highly degraded landscapes of Madagascar when closed canopy forest was nearby, we did not, even though our grassland and forest strips were surrounded by contiguous high‐quality habitat. Torppa et al .…”

“…secondary forest and agroforests) have similar community‐level attributes (species richness and abundance) to those found within old‐growth forests. In some cases, a high level of forest disturbance is associated with higher species diversity (Nichols et al ., 2007; Torppa et al ., 2020). Torppa (2020) found diverse communities of dung beetles in highly degraded landscapes, but only when closed canopy forest was relatively nearby.…”

Invertebrates and the complexity of tropical ecosystems

“…We touch on several such directions here. Well‐designed comparative approaches comparing ecological patterns across ecological gradients and boundaries produce new and more general insights (see Chatelain, Elias, Guilbert, & Soulier‐Perkins, ; Mottl, Fayle, Yombai, Novotný, & Klimeš, ; Rabl, Gottsberger, Brehm, Hofhansl, & Fiedler, ; Raine, Slade, & Lewis, , all available in this issue). Expanding attention into a wider spread of invertebrate taxa adds insights as a wider range of ecosystem functions is encompassed (see Chatelain et al, , Drinkwater, Williamson, Clare, & Rossiter, , Luke, and Phillips, Chung, Edgecombe, & Ellwood, , all available in this issue). Using the rapid response times of invertebrates in terrestrial ecosystems allows us to evaluate impacts of and recovery from environmental transformations due to natural and human actions (see Franca et al , Luke et al, , Stone, Shoo, Stork, Sheldon, & Catterall, , Torppa, Wirta, & Hanski, , all available in this issue). The availability of effectively limitless computing power potentially allows the enormous complexity of tropical food webs and distribution maps (see Scriven et al, , this issue) to be modeled realistically: Interpreting very complex model systems of course may be as challenging as contemplating the real thing (McLane, Semeniuk, Mcdermid, & Marceau, ). Aligning pattern and process: Does tropical biodiversity matter beyond its intrinsic value? Can ecosystem processes and service survive a massive decline in invertebrate species and density?…”

Tropical terrestrial invertebrates—Where to from here?

“…Although old‐growth forests should be prioritized due to their unmatched ability to support high levels of biodiversity, modified and degraded land should not be forgotten as they too provide suitable habitats for many species (Torppa, Wirta, & Hanski, , this issue). This is particularly relevant in areas where the proportion of primary habitats are diminished and where secondary or regenerating habitats provide refuge for many invertebrate species (Ewers et al, ).…”