Aura Mariela Alonso Rodríguez

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Oil palm expansion threatens tropical moth assemblages in southwestern Costa Rica

Oil palm is currently one of the most rapidly expanding crops throughout the tropics, yet little is known about its impacts on Neotropical biodiversity, especially for insect faunas. Responses of moth assemblages to land use change may substantially vary among taxa, depending on their functional traits and resource needs. In this study, geometrid and arctiine assemblages were surveyed in a tropical human dominated landscape of southwestern Costa Rica, where oil palm plantations have become the second commonest land cover after pastures. Moths were sampled during six months (Feb-Jul) with automatic funnel traps in four habitat types (interior and margin of old-growth forests, young secondary forests and oil palm plantations) inside a 30km² area. Geometrid and arctiine richness and diversity was high in the interior of old-growth forests as well as at forest margins and young secondary forests, but was severely reduced in oil palm plantations. Abundance patterns of both groups showed seasonality, with a decrease in abundance towards the wet season. Geometrid numbers were highest in the interior of old-growth forests and lowest in oil palm plantations, while arctiine numbers did not differ between habitats due to the presence of a few extremely common lichen moth species in oil palm plantations. Dominance values were highest in oil palm plantations, where one species of each group accounted for over 40% of total abundance. Species composition was distinct in the forest interior and oil palm plantation sites when compared to the other intermediately disturbed habitats. Vegetation structure was the strongest predictor for moth community composition, whereas microclimatic differences were hardly relevant. The results of this study confirm that tropical forest geometrid moths are more vulnerable to land use change and are more strongly bound to the interior of rain forests, showing higher potential as bioindicator species, while many arctiines are more adapted to thrive in disturbed habitats. Conservation strategies should focus not only on the protection of old-growth forest remnants, but also on the promotion of natural forest re-growth and structural complexity of degraded habitats. Although successional forests harbor different species composition than old-growth forests, they may ameliorate biodiversity loss in the face of continuous oil palm expansion, which may have severe repercussions on the structure of ecological food webs and provisioning of ecosystem services in human dominated landscapes.

Author: Aura Mariela Alonso Rodríguez

Supervisors: Bryan Finegan, Konrad Fiedler

Institution: Center for Tropical Agricultural Research and Education (CATIE),Turrialba, COSTA RICA

Study program: Master in Management and Conservation of Tropical Forests & Biodiversity