The effect of habitat type and month on variation in community structure of fruit and frugivorous Lepidoptera in a tropical lowland forest landscape
Date: 4 April 2022
Thesis or dissertation
University of Exeter
MSC by Research Biological Sciences
Tropical rainforests are one of the most diverse biomes on the planet and provide vital ecological services, including climate regulation through carbon sequestration. Borneo has incredibly high biodiversity that is under threat due to anthropogenic pressure, which leads to widespread deforestation due to mining, logging and the ...
Tropical rainforests are one of the most diverse biomes on the planet and provide vital ecological services, including climate regulation through carbon sequestration. Borneo has incredibly high biodiversity that is under threat due to anthropogenic pressure, which leads to widespread deforestation due to mining, logging and the conversion of land to plantations. Protecting this biodiversity, as well as documenting and monitoring it to inform conservation strategies, are of great priority. This study centres on the unprotected Rungan Forest Landscape in Central Kalimantan Province, Indonesian Borneo. This lowland forest is a mosaic of different habitats, including peat swamp forests (Low Pole), the sandy soil heath forest (Kerangas) and a transitional forest between the two (Mixed Swamp). Peatlands are relatively well studied and are known to be a key habitat for critically endangered species such as orangutans (Pongo pygmaeus) as well as storing large quantities of carbon. Lowland Kerangas habitats, on the other hand are less well studied and, unlike peat forest, are currently not represented in any protected areas, despite its potential to harbour a rich and unique biodiversity. High heterogeneity in the Rungan landscape is hypothesised to allow it to support higher biodiversity than expected from peat swamp or Kerangas by itself, due to habitat complementarity, but this has not yet been tested. Here, I investigate this by studying spatial and temporal variation in the community of frugivorous Lepidoptera and their fruit resources. Using ground fruit surveys and baited Lepidoptera traps, 17 plots of three different habitats (Kerangas, Mixed Swamp and Low Pole) were surveyed monthly for five consecutive months between April and August 2019. In chapter 2 I use this data to test whether there are significant differences in frugivorous Lepidoptera abundance, richness and diversity between the habitat types and months and whether this correlates with variation in fruit abundance, richness and diversity. I show that there are significant differences in: fruit abundance and diversity; butterfly abundance; and moth abundance and species richness. I also show that there was no correlation between Lepidoptera abundance, richness and diversity with fruit abundance, richness and diversity. In chapter 3 I use the same data set to test whether species composition of Lepidoptera and fruit differs between the habitats. Secondly, I test whether similarity in Lepidoptera species composition among sample sites correlates with similarity in fruit species composition among sample sites. Thirdly, I test for spatial correlation in species composition regardless of habitat. I show that species composition of Lepidoptera and fruit differs between the habitats and has a correlation between them. Finally I show there is spatial correlation within the study. Temporal variation in abundance, richness and diversity over the five study months indicates that further study is required to identify the drivers of this, for example seasonality, which may lead to asynchrony in resource availability among the habitats, providing a further source of complementarity. Further, it is noted that among Lepidoptera, the results are not always consistent between moths and butterflies and this raises questions about assumptions underlaying the use of ‘indicator taxa’, such as butterflies. Using this study as a baseline for community structures across several habitats and months, future surveys will be able to quickly detect any changes due to any external pressures like mining or fragmentation due to logging. Being able to quickly identify the effect of such threats on community structures can help guide protection measures. Together, the results indicate that the heterogeneous landscape could be leading to greater overall species diversity of the region, and therefore the principal of habitat complementarity stresses that all the habitats within the mosaic of the Rungan landscape should be protected.
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