The surrounding landscape influences the diversity of leaf-litter ants in riparian cloud forest remnants

Abstract

Riparian vegetation is a distinctive and ecologically important element of landscapes worldwide. However, the relative influence of the surrounding landscape on the conservation of the biodiversity of riparian remnants in human-modified tropical landscapes is poorly understood. We studied the surrounding landscape to evaluate its influence on leaf-litter-ant alpha and beta diversity in riparian remnants in the tropical montane cloud forest region of central Veracruz, Mexico. Sampling was carried out in 12 sites with riparian vegetation during both rainy (2011) and dry (2012) seasons. Ten leaf-litter samples were collected along a 100-m transect per site and processed with Berlese-Tullgren funnels and Winkler sacks. Using remotely-sensed and ground-collected data, we characterized the landscape around each site according to nine land cover types and computed metrics of landscape composition and configuration. We collected a total of 8,684 ant individuals belonging to 53 species, 22 genera, 11 tribes, and 7 subfamilies. Species richness and the diversity of Shannon and Simpson increased significantly in remnants immersed in landscapes with a high percentage of riparian land cover and a low percentage of land covers with areas reforested with Pinus, cattle pastures, and human settlements and infrastructure. The composition of ant assemblages was a function of the percentage of riparian land cover in the landscape. This study found evidence that leaf-litter ants, a highly specialized guild of arthropods, are mainly impacted by landscape composition and the configuration of the focal remnant. Maintaining or improving the surrounding landscape quality of riparian vegetation remnants can stimulate the movement of biodiversity among forest and riparian remnants and foster the provision of ecosystem services by these ecosystems. Effective outcomes may be achieved by considering scientific knowledge during the early stages of riparian policy formulation, in addition to integrating riparian management strategies with broader environmental planning instruments.

Fig 1. Location of the study sites in central Veracruz, Mexico.

The red circles represent 200-m-buffers around each remnant of riparian vegetation where leaf-litter ants were sampled. Blue lines are the tributaries of the Antigua River watershed. In the inset are indicated the location, in Mexico, of the study area (red square), the state of Veracruz (black polygon), and the location of Mexico (white polygon) between North and Central America. This map was generated by the first author (MAGM) using ArcGIS 10.2^® and vector data models available in the GIS website of the Mexican commission for the knowledge and use of biodiversity (CONABIO, http://www.conabio.gob.mx/informacion/gis/) under a CC BY license.

Fig 2. Landscape predictors included in the 95% confidence set of the models (gray bars) and in the ΔAICc < 2 set of the models (black bars) for explaining the abundance, species richness, Shannon, and Simpson diversity of leaf-litter ant assemblages associated with remnants of riparian vegetation in central Veracruz, Mexico.

The importance of each predictor is shown by the sum of Akaike weights (∑w_i, panels in the left side). Panels on the right side indicate the values of the averaged model parameter estimates (β) ± unconditional variance of information-theory-based model selection and multi-model inference. The sign (±) of parameter estimates represents a positive or negative effect of the predictor on the diversity measures. The goodness-of-fit of each multiple model is indicated in each panel as the percentage of deviance explained by each multiple model. The predictors are the percentage of riparian land cover (RL) and tropical montane cloud forest land cover (FL) within the surrounding landscape, the shape (SI) and width (WR) of the focal riparian remnant.

Fig 3. Landscape predictors included in the 95% confidence set of the models (gray bars) and in the ΔAICc < 2 set of the models (black bars) for explaining the compositional similarity indicated by Jaccard, Sørensen, and Morisita-Horn indices of leaf-litter ant assemblages associated with remnants of riparian vegetation in central Veracruz, Mexico.

The importance of each predictor is shown by the sum of Akaike weights (∑w_i, panels in the left side). Panels on the right side indicate the values of the averaged model parameter estimates (β) ± unconditional variance of information-theory-based model selection and multi-model inference. The sign (±) of parameter estimates represents a positive or negative effect of the predictor on the diversity measures. The goodness-of-fit of each multiple model is indicated in each panel as the percentage of total variation explained by each multiple model. The predictors are the percentage of riparian land cover (RL) and tropical montane cloud forest land cover (FL) within the surrounding landscape, the shape (SI) and width (WR) of the focal riparian remnant.