Lizards as a Lens for Understanding the Effects of Land Use Change
Keywords: Reptiles
Land Use Change
Oil palm
Costa Rica
Community Ecology
Monoculture
Polyculture
Microhabitats
Forest-dependent Species
Disturbance-tolerant Species
Anoles
Lizards
Text
Thesis

Humans consume more metric tons of oil palm (OP) than any other vegetable oil. Growing global demand is creating an OP boom in the Neotropics, where plantations cause deforestation, habitat fragmentation, and drive biodiversity loss. Considering the long-term volatility and consequences of OP plantations (OPPs), farmers increasingly appreciate the value of assessing the potential benefits of combining OP production with other foods and cash crops. Local farming families, who have guided the Iniciativa Osa y Golfito (INOGO) since its inception, view shifting away from plantation monocultures towards smallholder-run polycultures as a welcome change with socioecological benefits. This study, part of a grander INOGO effort, quantifies and details how smallholder OP polycultures and paired, adjacent monocultures affect species composition and diversity of Anolis lizards. I conducted over 400 hours of visual encounter surveys in eight pairs of family-owned OP farms, half-hectare monocultures bordering half-hectare polycultures (palm intermingled with cacao, bananas, and Laurel timber trees). The 192 farm surveys were split evenly between the rainy and dry seasons, day and night, and the two farming practices. I conducted additional surveys in four local primary and secondary forest sites, to compare anole community diversity with the two types of OP farms. Anole abundance was greatest in the rainy season and during diurnal surveys, while species richness was highest in the rainy season and during nocturnal surveys. In the farms, I recorded 1,656 anoles from seven species, 65% of which were in the polycultures. In the forests, I found 128 anoles across six species, two of which were unique to forested habitats. Although species richness does not significantly differ between habitat types, when assessing higher order Hill numbers, Shannon diversity (q=1) and Simpson diversity (q=2), a clear gradient of increasing biological diversity from monocultures to polycultures to forests is evident. This is likely because the polycultures restore vital forest microhabitats like leaf litter, low perching sites, and closed canopies, whereas the monocultures are shown to be more open and have greater grass coverage. Consequently, I find forest-reliant species, A. polylepis and A. osa, to be significantly more abundant in the polycultures, while the disturbance-tolerant A. limifrons is the lone abundant species in all monocultures. Additionally, this study details the first documented population of A. auratus in Costa Rica. I recorded 42 encounters with this species in one of the eight experimental farms, Salamá, and none across the other seven sites, indicating that Salamá could be a point of colonization for this lizard as it continually moves northward along an intensive agricultural corridor. The A. auratus is significantly more abundant in the Salamá monoculture than the paired polyculture, likely because the former more closely resembles its native savanna habitat. This introduced lizard is the only species to show a significant association with the monoculture treatment. Therefore, I postulate that conversion of plantations to polycultures via intermingling other high-value crops could reduce the spread of non-native, and potentially invasive, species better adapted to thrive in disturbed landscapes. I emphasize the importance of diversifying OP plantations to help species reliant upon forest-associated microhabitats like Anolis osa and Anolis polylepis. While I show that neither farm type has the potential to support truly forest-dependent species like Anolis aquaticus and Anolis capito, I assert that biologically enriched smallholder farms, through inclusion of vital microhabitats, higher crop diversity, and increased structural heterogeneity, offer better support for forest-associated lizards than their monoculture counterparts. Ultimately, both smallholder practices, monocultures and polycultures, are shown to harbor greater biodiversity than large-scale plantations previously surveyed in the same region. Given the expansion of OPPs in the tropics, my findings are of broad significance.