Papers by Freerk Molleman
International Journal of Primatology, 2015
Intestinal parasites may constitute an important evolutionary and ecological force. Our aim was t... more Intestinal parasites may constitute an important evolutionary and ecological force. Our aim was to identify social, physiological, and environmental factors that correlate with intestinal parasite infections in adult male gray-cheeked mangabeys (Lophocebus albigena). We analyzed 102 fecal samples collected over 19 months from 18 adult males for the incidence (proportions of samples with parasites) and intensity (total number of parasites per gram of feces) of infection of nematodes relative to social status, fecal glucocorticoid and testosterone metabolites, group size, and rainfall, all of which are factors that earlier studies suggested can be important mediators of parasite load. Parasite incidence was greater in immigrant males compared to low-and high-ranking males whereas parasite intensity was greater in immigrant males and low-ranking males compared to high-ranking males. Fecal samples with more parasites had higher concentrations of fecal glucocorticoid and testosterone metabolites than fecal samples with fewer parasites. As immigrant males had a greater incidence of parasites and higher concentrations of both metabolites than resident males, this profile appears to fit immigrant males best. We also found higher nematode intensities in mid-sized groups, and during periods with more rainfall. Our results suggest that it will be fruitful for future studies to explore the role of immigrant males as spreaders of intestinal parasites.
Dispersal limitation has been considered to decrease with body size in animals and to be an impor... more Dispersal limitation has been considered to decrease with body size in animals and to be an important factor limiting community assembly on spatially isolated patches. Here we hypothesize that for flightless bark-dwelling oribatid mites dispersal limitation onto young trees might increase with body size (due to a decrease in aerial dispersal capacities), and it might occur even within a spatially contiguous forest canopy. We suppressed dispersal limitation towards branches from young trees by physically connecting them to branches from old trees and analyzed the impacts on community composition, accounting for branch microhabitat variables. Suppression of dispersal limitation increased community evenness and mean body size of mites on branches from young trees. Across all species, large species body-size corresponds to an abundance increase after suppression of dispersal limitation. Consistently, on no-contact control branches, mite body-sizes were larger on branches from old compared to young trees. Our study suggests that colonization/performance trade-offs might affect community assembly even across seemingly contiguous habitats. Overall, a previously underappreciated factor selecting against large body size in flightless canopy-dwelling invertebrates might be that large bodies makes these invertebrates fall faster and disperse less, not more. Islands are places that are hard to reach and dispersal may hence limit the assembly of species communities on islands (we define community assembly as the processes controlling which species establish at which abundances in a community). Island biogeography usually focuses on oceanic islands or habitat islands of hectares in size and isolated by kilometres 1. However, dispersal limitation –the limitation in the ability of organisms to reach a given locality-might affect community assembly also at much smaller scales: Large organisms may be hosts for small, flightless organisms that live inside or on the host and are unable to migrate actively between hosts, even if these hosts are spatially proximate 2,3. Possible examples include macroparasites living inside social mammals 4 or mites living on the bark of forest trees 5. For such communities, individual hosts might act as islands, limiting coloniza-tion even across the short distances among hosts. Effects of such dispersal limitation on communities on hosts are particularly likely if hosts are young, because time for colonization was short, and because young hosts are small, harboring particularly small colonizer populations facing particularly high risks of extinction that would need to be compensated by particularly frequent recolonizations 3. Dispersal assembly of local communities on islands is often described by " neutral " models that treat dispersal as a random process in which differences between species are unimportant for the establishment success of species 6,7. However, dispersal limitation is to some extent deterministic as species differ in their capacity to disperse, and this capacity may be negatively traded off against performance such as competitiveness or stress tolerance 8–11. Specifically, for macroscopic animals, dispersal limitation is often considered to increase with a decrease in body size as smaller animals spend proportionally more energy for locomotion and have proportionally less energy at their disposal 12–14. However, in the case of flightless colonizers on hosts such as in many mite species, dispersal is often passive by floating through the air among hosts. Dispersal is hence not limited by available energy, but by
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Papers by Freerk Molleman