Abstract:

Habitat loss and fragmentation are the main threats to biodiversity in tropical forests. Agroecosystems such as shaded cocoa plantations (SCP) provide refuge for tropical forest biota. However, it is poorly known whether the interspecific ecological interactions are also maintained in these transformed habitats. We evaluated the diversity, reproductive status and photosynthetic metabolism (CAM or C₃) of the epiphytic orchid community, and their interactions with host trees (phorophytes) in SCP compared to tropical rainforest (TRF).

In southeastern Mexico, three sites each in TRF and SCP were studied, with four 400 m2 plots established at each site to record all orchids and their phorophytes. We determined the reproductive (adult) or non-reproductive (juvenile) status of each orchid individual in relation to the presence or absence, respectively, of flowers/fruits (or remnants), and assigned the photosynthetic pathway of each orchid species based in literature. We used true diversity and ecological networks approaches to analyze orchid diversity and orchid–phorophyte interactions, respectively.

In total, 607 individuals belonging to 47 orchid species were recorded. Orchid diversity was higher in TRF (19 effective species) than in SCP (11 effective species) and only seven species were shared between the two habitats. CAM orchid species were more frequent in SCP (53%) than in TRF (14%). At the community level the proportion of non-reproductive and reproductive orchid species and the nested structure and specialization level of the TRF orchid–phorophyte network were maintained in SCP. However, only a subset of TRF epiphytic orchids remains in SCP, highlighting the importance of protecting TRF. Despite this difference, shaded agroecosystems such as SCP can maintain some of the diversity and functions of natural forests, since the SCP epiphytic orchid community, mainly composed of CAM species, and its phorophytes constitute a nested interaction network, which would confer robustness to disturbances.

Key words: agroecosystem, ecological networks, Mexico, photosynthetic pathway, tropical rainforest