Negative impacts of human land use on dung beetle functional diversity

Abstract

The loss of biodiversity caused by human activity is assumed to alter ecosystem functioning. However our understanding of the magnitude of the effect of these changes on functional diversity and their impact on the dynamics of ecological processes is still limited. We analyzed the functional diversity of copro-necrophagous beetles under different conditions of land use in three Mexican biosphere reserves. In Montes Azules pastures, forest fragments and continuous rainforest were analyzed, in Los Tuxtlas rainforest fragments of different sizes were analyzed and in Barranca de Metztitlán two types of xerophile scrub with different degrees of disturbance from grazing were analyzed. We assigned dung beetle species to functional groups based on food relocation, beetle size, daily activity period and food preferences, and as measures of functional diversity we used estimates based on multivariate methods. In Montes Azules functional richness was lower in the pastures than in continuous rainforest and rainforest fragments, but fragments and continuous forest include functionally redundant species. In small rainforest fragments (<5 ha) in Los Tuxtlas, dung beetle functional richness was lower than in large rainforest fragments (>20 ha). Functional evenness and functional dispersion did not vary among habitat types or fragment size in these reserves. In contrast, in Metztitlán, functional richness and functional dispersion were different among the vegetation types, but differences were not related to the degree of disturbance by grazing. More redundant species were found in submontane than in crassicaule scrub. For the first time, a decrease in the functional diversity in communities of copro-necrophagous beetles resulting from changes in land use is documented, the potential implications for ecosystem functioning are discussed and a series of variables that could improve the evaluation of functional diversity for this biological group is proposed.

Figure 1. Dendrogram of the species forming functional groups.

Functional groups were considered at an arbitrary Euclidian distance of 1.5 (dotted line). The branch length of these dendrograms was used to analyze dung beetle functional diversity (FD) in (A) the Montes Azules Biosphere Reserve, (B) the Los Tuxtlas Biosphere Reserve, and (C) the Barranca de Metztitlán Biosphere Reserve. The names of the functional groups are combinations of the following characteristics: S = small, L = Large, Pa = paracoprid, En = endocoprid, Te = telecoprid, D = diurnal, N = nocturnal, Ge = generalist, Co = coprophage, Ne = necrophage, and TS = trophic specialist.

Figure 2. Species richness and number of dung beetles per functional group.

The figure shows the communities from (A) Montes Azules, (B) Los Tuxtlas and (C) Barranca de Metztitlán. The names of the functional groups are combinations of the following characteristics: S = small, L = Large, Pa = paracoprid, En = endocoprid, Te = telecoprid, D = diurnal, N = nocturnal, Ge = generalist, Co = coprophage, Ne = necrophage, and TS = trophic specialist.

Figure 3. Mean values of functional diversity for the dung beetle communities under different habitat conditions.

(A) Montes Azules, (B) Los Tuxtlas and (C) Barranca de Metztitlán. Error bars are standard error. The value of FR_D (functional richness) is based on dendrogram length, FR_V (funcional richness) is a convex hull volume of functional space, FEve (functional evenness) is the regularity with wich the functional space is filled by species, weighteg by their abundance, and FDis (functional dispersion) is the mean distance of individual species to the centroid of all species in the community.

Figure 4. Functionally singular and redundant species in each local community.

The complete bar indicates the total number of species in each community, the white segment corresponds to the functionally singular species and the black segment to the redundant species. (A) Montes Azules, (B) Los Tuxtlas and (C) Barranca de Metztitlán.