Patterns of vertebrate biodiversity in a tropical dry and mangrove forest matrix / Patrones de biodiversidad de vertebrados en una matriz de bosque seco tropical y manglar

Introduction: Tropical dry forests and mangroves, two of the world's most endangered ecosystems, each host a different set of environmental conditions which may support unique assemblages of species. However, few studies have looked at the unique vertebrate biodiversity in regions where both habitats occur side-by-side. Objective: To assess the vertebrate diversity and patterns of habitat usage in a mangrove and tropical dry forest matrix in an unprotected region of Northwestern Costa Rica. Methods: The study was conducted in a 7 km2 matrix of mangrove and tropical dry forests between Cabuyal and Zapotillal bays in Northwestern Costa Rica, south of Santa Rosa National Park. From September 2017 to March 2018, we used 13 automatic camera traps over 1 498 trap days to capture species utilizing the region and assess their patterns of habitat usage both spatially and temporally. Results: Seventy vertebrate species from 42 families in 27 orders were detected, including several globally threatened species. Over half of all species were detected in only one habitat, particularly amongst avian (78 %) and mammalian (42 %) species. Tropical dry forests hosted the greatest number of unique species and supported a greater percentage of herbivores than mangrove or edge habitats, which were dominated by carnivorous and omnivorous species. Mean detections per camera trap of all species increased significantly from the coldest and wettest month (Oct) to the hottest and driest months (Jan & Feb) in tropical dry forests. Sample-based rarefaction analysis revealed that survey length was sufficient to sample the tropical dry forest and edge habitats, though mangroves require further sampling. Conclusions: Taxa found to utilize different forest types may utilize each for different stages of their life cycle, moving between areas as environmental conditions change throughout the year. General patterns of global biodiversity favoring carnivore and omnivore usage of mangrove forests was confirmed in our study.

Introducción: Los bosques secos tropicales y los manglares, dos de los ecosistemas más amenazados del mundo, albergan cada uno un grupo de condiciones ambientales que pueden albergar conjuntos únicos de especies. Sin embargo, pocos estudios han analizado la biodiversidad única de vertebrados en regiones donde ambos hábitats se encuentran uno al lado del otro. Objetivo: Evaluar la diversidad de vertebrados y los patrones de uso del hábitat en una matriz de manglar y bosque seco tropical en una región no protegida del noroeste de Costa Rica. Métodos: El estudio se realizó en una matriz de 7 km2 de manglares y bosques secos tropicales en las bahías de Cabuyal y Zapotillal en el noroeste de Costa Rica, al sur del Parque Nacional Santa Rosa. De septiembre 2017 a marzo 2018, utilizamos 13 cámaras trampa automáticas durante 1 498 días trampa para capturar especies que utilizan la región y evaluar sus patrones de uso espacial y temporal del hábitat. Resultados: Se detectaron 70 especies de vertebrados de 42 familias y 27 órdenes, incluidas varias especies amenazadas a nivel mundial. Más de la mitad de todas las especies se encontraron en un solo hábitat, particularmente aves (78 %) y mamíferos (42 %). Los bosques secos tropicales albergan el mayor número de especies únicas y sustentan un mayor porcentaje de herbívoros que los hábitats de borde de manglares, que estaban dominados u hospedados por especies carnívoras y omnívoras. Las detecciones promedio por cámara trampa de todas las especies aumentaron significativamente desde el mes más frío y húmedo (octubre) hasta los meses más cálidos y secos (enero y febrero) en los bosques secos tropicales. El análisis de rarefacción basado en muestras reveló que la duración del estudio fue suficiente para muestrear los hábitats de bosque seco tropical y de borde, aunque los manglares requieren más muestreo. Conclusiones: Se encontró que los taxones pueden usar varios tipos de bosque en las diferentes etapas de su ciclo de vida, moviéndose entre áreas a medida que las condiciones ambientales cambian a lo largo del año. En nuestro estudio se confirmaron patrones generales de la biodiversidad global que favorecen el uso de los bosques de manglar por parte de carnívoros y omnívoros.

Using Unmanned Aerial Systems (UAS) to assay mangrove estuaries on the Pacific coast of Costa Rica.

Mangrove forests, one of the world's most endangered ecosystems, are also some of the most difficult to access. This is especially true along the Pacific coast of Costa Rica, where 99% of the country's mangroves occur. Unmanned Aerial Systems (UAS), or drones, have become a convenient tool for natural area assessment, and offer a solution to the problems of remote mangrove monitoring. This study is the first to use UAS to analyze the structure of a mangrove forests within Central America. Our goals were to (1) determine the forest structure of two estuaries in northwestern Costa Rica through traditional ground measurements, (2) assess the accuracy of UAS measurements of canopy height and percent coverage and (3) determine whether the normalized difference vegetation index (NDVI) could discriminate between the most abundant mangrove species. We flew a UAS equipped with a single NDVI sensor during the peak wet (Sept-Nov) and dry (Jan-Feb) seasons. The structure and species composition of the estuaries showed a possible transition between the wet mangroves of southern Costa Rica and the drier northern mangroves. UAS-derived measurements at 100 cm/pixel resolution of percent canopy coverage and maximum and mean canopy height were not statistically different from ground measurements (p > 0.05). However, there were differences in mean canopy height at 10 cm/pixel resolution (p = 0.043), indicating diminished returns in accuracy as resolution becomes extremely fine. Mean NDVI values of Avicennia germinans (most abundant species) changed significantly between seasons (p < 0.001). Mean NDVI of Rhizophora racemosa (second most abundant species) was significantly different from A. germinans and dry forest dominant plots during the dry season (p < 0.001), demonstrating NDVI's capability of discriminating mangrove species. This study provides the first structural assessment of the studied estuaries and a framework for future studies of mangroves using UAS.