No abstract

Dung beetles relocate vertebrate feces under the soil surface, and this behavior has many ecological consequences. In tropical forests, for example, seeds defecated by mammals that are subsequently buried by dung beetles are less likely to suffer predation. While the effects of dung beetles on the fate of defecated seeds have been relatively well studied, their effect on seeds already buried in the soil has not. To contribute to fill this gap, we designed a study with three objectives: (a) Describe the vertical re-distribution of soil seeds that occurs due to dung beetle activity; (b) Determine if beetle activity favors establishment of seedlings from the soil seed bank; and (c) Determine if the effect of dung beetles is stronger in sites of recurrent mammal defecation. We carried out three complementary field experiments, one with artificial seeds (plastic beads) of three sizes buried at known depths, one with two species of seeds buried at those same depths, and one with the natural soil seed bank in sites of single vs. recurrent defecation. Buried beads were moved by dung beetles along the vertical axis, both upwards (9.5%) and downwards (11.5%); smaller beads were more frequently moved downwards while the contrary occurred for larger beads. Dung beetle activity caused an increase in seedling establishment, both from experimentally buried seeds and from the natural seed bank. Defecation recurrence had no effect on seedling establishment. We conclude that dung beetle activity affects seed bank dynamics with important consequences for seedling establishment in tropical forests.Abstract in Spanish is available with online material.

Dung beetles are secondary seed dispersers, incidentally moving many of the seeds defecated by mammals vertically (seed burial) and/or horizontally as they process and relocate dung. Although several studies have quantified this ecological function of dung beetles, very few have followed seed fate until seedling establishment, and most of these have focused on the effects of seed burial. We know very little about the effects of horizontal seed movement by dung beetles, though it is generally assumed that it will affect plant recruitment positively through diminishing seed clumping. The objective of our study was to assess the effects of dung beetle activity on the spatial distribution of seeds and seedlings, and on the probability of seedling establishment. In a tropical rainforest in Mexico we carried out two complementary field experiments for each of two tree species (Bursera simaruba and Poulsenia armata), using seeds experimentally imbedded in pig dung and recording their fate and spatial location over time. For both species, dung beetle activity reduced the spatial clumping of seeds and seedlings; however, it did not increase the probability of seedling establishment. We discuss the context- and species-specificity of the combined effects of horizontal and vertical dispersal of seeds by dung beetles, and the need to quantify long-term seedling fates to more accurately determine the effects of seed movement by dung beetles on plant recruitment.

Dung beetle activity causes many changes in the soil when they remove feces from the surface. In temperate grasslands and in greenhouse experiments, these changes have been found to positively affect established plants, but information about these effects under natural conditions in tropical forests is practically nonexistent. In a tropical rainforest (Los Tuxtlas, Mexico), we carried out field experiments with seedlings of six tree species (Brosimum alicastrum, Calophyllum brasiliense, Cymbopetalum baillonii, Diospyros digyna, Omphalea oleifera, and Poulsenia armata), to assess whether feces burial by dung beetles had any positive effect on them. We estimated foliar nitrogen and phosphorus, seedling survival, growth and resource allocation, under three treatment levels: (a) feces added and beetles active, (b) feces added and beetles excluded, and (c) no feces added (and consequently no beetles active). We analyzed data at two levels: community (all plant species together) and individual species. Dung beetle activity did not increase the concentration of foliar nutrients or seedling performance (survival, growth); in one species, it modified resource allocation. At the community level and for two species, dung beetle activity decreased the probability of seedlings growing in height. Our study provides evidence on how extrapolating the effects of dung beetle activity from other study systems into tropical forests can be problematic. More studies will be needed before we can have a clearer idea of the effects that feces burial by dung beetles have on established plants in tropical forests.

Se presenta el registro fotográfico de Puma yagouaroundi (yaguarundí) en el área de amortiguamiento de la Reserva de la Biosfera Zicuirán-Infiernillo. Las fotografías fueron tomadas con cámaras trampa instaladas de octubre de 2013 a octubre de 2014. Con esta evidencia se documenta la presencia de esta especie en la parte baja de la depresión del Balsas, y se sugiere que su distribución a lo largo de la sierra Madre del Sur y la zona costera de Michoacán podría tener conectividad hacia esta zona. Derechos Reservados © 2016 Universidad Nacional Autónoma de México, Instituto de Biología. Este es un artículo de acceso abierto distribuido bajo los términos de la Licencia Creative Commons CC BY-NC-ND 4.0.