The ecology of saprophagous macroarthropods (millipedes, woodlice) in the context of global change

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Abstract
Millipedes (Diplopoda) and woodlice (Crustacea, Isopoda), with a total of about 15000 described species worldwide, contribute substantially to invertebrate biodiversity. These saprophagous macroarthropods, which are key regulators of plant litter decomposition, play an important role in the functioning of terrestrial ecosystems in tropical and temperate areas. Herein we review current knowledge on the effects of climate, food quality and land cover on millipede and woodlouse species to explore their potential responses to global change. Essentially similar trends are observed in the two taxa. Experiments have shown that climate warming could result in higher rates of population growth and have positive effects on the abundance of some temperate species. This is consistent with signs of northward expansion in Europe, although the mechanisms of dispersal remain unclear. The generality of this finding is evaluated in relation to the life histories and geographical distributions of species. At low latitudes, interactions with more severe droughts are likely and could affect community composition. Elevated atmospheric CO₂ levels and changes in plant community composition are expected to alter leaf litter quality, a major determinant of macroarthropod fertility via the link with female adult body size. Although food quality changes have been shown to influence population growth rates significantly, it is proposed that the effects of warming will be probably more important during the coming decades. Land cover changes, mainly due to deforestation in the tropics and land abandonment in Europe, are critical to habitat specialists and could override any other effect of global change. Habitat destruction by man may be the main threat to macroarthropod species, many of which are narrow endemics. At the landscape scale, habitat heterogeneity could be a good option for conservation, even at the cost of some fragmentation. Two principal areas are identified which require further work: (i) the effects of climate change across broader geographic ranges, and on species with different ecologies and life histories; (ii) the effects of global change on both macroarthropods and their natural enemies (predators, parasites and pathogens), to improve predictions in field situations.