Abundance and Diversity of Brazil Nut Pollinators and Orchid Bees in Secondary and Primary Forest Habitats in East Amazon
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Abundance and Diversity of Brazil nut pollinators and Orchid bees in Secondary and Primary forest habitats in East Amazon Sara Hellström Master thesis 30 credits Supervisor: Dr. Yann Clough Conservation Biology Dept. of Biology Faculty of Science Lund University 2017 Abstract The Brazil nut tree (Bertholletia excelsa) produces Brazil nuts, an economically important non-timber forest product. As land-conversion from forest to field increases throughout the Brazil nut tree’s range, many trees end up being the only remaining mature tree in open fields or in secondary forest. The Brazil nut tree is dependent on a variety of large bees for pollination and fruit set. It is therefore essential to investigate how landscape changes affects the tree’s pollination services. In order to see if abundance and composition of the pollinator community differs between degraded, secondary forest and older, continuous forests where Brazil nut is harvested, the Orchid bee (Euglossinae) community together with other known Brazil nut pollinators were sampled using fragrance baits. Data on average per-tree fruit yield was gathered and compared between landscape types, and production was compared with pollinator abundance. The study suggests that both orchid bee and other Brazil nut pollinator abundance is higher in degraded sites compared to primary forest sites, while species richness and composition remains unaffected. This may be due to a spike in pollen and nectar resources following slash-and-burn practices, leading to pollinators being more concentrated in degraded, secondary growth forests close to agricultural fields. There was no correlation between pollinator abundance and production. To further investigate how land conversion and fragmentation affects Brazil nut pollination services, direct observational studies of pollinators as well as studies on foraging ranges, pollen and nectar resource availability and nest prevalence are warranted. Contents Introduction ..................................................................................................................................................................... 1 Methods ........................................................................................................................................................................... 3 Study organisms ........................................................................................................................................................ 3 Study sites ................................................................................................................................................................... 5 Sampling method ...................................................................................................................................................... 7 Per-tree fruit count .................................................................................................................................................... 8 Statistical analysis ..................................................................................................................................................... 9 Results ............................................................................................................................................................................ 10 Orchid bee inventory .............................................................................................................................................. 10 Brazil nut pollinator abundance ........................................................................................................................... 11 Production ................................................................................................................................................................. 12 Discussion ..................................................................................................................................................................... 14 Acknowledgements ..................................................................................................................................................... 17 References ................................................................................................................................................................... 18 1 Introduction The Amazon rainforest has seen large areas subjected to logging and land conversion, leading to biodiversity loss and impacting local and global climate (Ochoa‐Quintero et al., 2015, Barlow et al., 2016). The livelihood of people in rural areas is often dependent on detrimental practices such as logging, clear-cutting for cattle grazing or mining. As an alternative source of income that entails less negative impact on forest ecosystems, collecting so-called Non-Timber Forest Products (NTFPs) are presented as an opportunity (Nepstad and Schwartzman, 1992, Clay, 1997). These are products such as fruits, nuts, reisins, leaves and bark that can be harvested directly from a mature forest without felling trees. For this reason, there has been an increased interest in promoting these products on international markets in order to provide a non-destructive means of income to forest holders. However, its long-term economic viability in the face of rapid modernization and global market fluctuations has been questioned (Terborgh and Peres, 2017, Arnold and Pérez, 2001). Nevertheless, as forest degradation increases, it is of great importance to investigate how this affects the productivity of NTFP species in order to guide optimal harvesting and management practices. One of the most economically important NTFPs in the Amazon region is Brazil nuts. The Brazil nut tree (Bertholletia excelsa Humboldt & Bomplant) is a signature species of the Amazon rainforest, often towering above the surrounding canopy. The edible seeds have been a food source for humans in the Amazon basin since prehistoric times, and there are indications of humans playing a role in dispersing the tree to its current range (Shepard and Ramirez, 2011). Today, the Brazil nut tree can be found in lowland tropical humid forest from eastern Brazil to the Andes in the west. The seed (called Brazil nut, Para nut, Amazon nut or castaña) is an important export product for Peru, Bolivia and Brazil, as well as a locally traded commodity providing a supplementary income for small-time farmers (Coslovsky, 2014). The majority of nuts are harvested directly from wild trees, making it a prime example of a NTFP (Clay, 1997). The long-term economic value to forest owners has made it a subject of much legislation, and the trees are legally protected in Brazil, Bolivia and Peru (Guariguata et al., 2010, Cronkleton et al., 2012). Timber extraction, both legal and illegal, is an integral part of forest use in most areas where Brazil nut harvesting takes place, and it has been shown that selective logging can be combined with Brazil nut harvesting without significant productivity loss (Rockwell et al., 2015) nor decreased sapling regeneration (Soriano et al., 2012). However, since Brazil nut trees are legally protected, they are often the only mature trees left after the rest of the forest has been logged or burned in favor of agriculture or cattle farming. Little research has been done on how these trees fare in 2 highly disturbed, fragmented landscapes. The Brazil nut tree is self-sterile, and fruit set is dependent on pollination by large bees. For pollinator-dependent species, isolation and fragmented populations will lead to reduced seed set due to pollen limitation (Ghazoul, 2005). Thus, for trees left in a fragmented landscape, the pollination services necessary for fruit set might be under threat. Neotropical bees populations tied to forest habitats are most likely affected by deforestation and agricultural intensification, though lack of knowledge on range, food sources and life cycle traits makes predictions difficult for many species (Freitas et al., 2009). In tropical regions, 98% of plant species are dependent on insect pollination (Ollerton et al., 2011) including most crop species. Yield is positively related to native wild bee species richness and abundance for important crops such as coffee (Klein et al., 2003), cashew (Freitas B. M. et al., 2014), and passion fruit (Yamamoto et al., 2012). Habitat fragmentation following deforestation threatens pollination services for many plant species, leading to decreased pollen deposit and fruit set (Rocha and Aguilar, 2001, Cunningham, 2000, Ghazoul, 2005) as well as increased inbreeding frequencies (Lamont et al., 1993). Since the Brazil nut tree has very large and heavy seed pods that rarely get dispersed over long distances, clustered groups of trees are predicted to be related (Mori and Prance, 1990). For this reason, pollinators capable of traveling long distances are essential for genetic mixing. A key family of pollinators for Brazil nut and many other low-density plant species in tropical environment are orchid bees (Euglossinae). They are capable of flying long distances, and regularly visit the same resources within their home range, making them important vectors for long-distance gene transfer (Janzen, 1971, Wikelski et al., 2010). A decrease in pollinator abundance and mobility could lead to lower rates of cross-individual pollen deposits, increasing inbreeding frequencies and thus pose a threat to the short-term productivity and long- term regeneration capabilities of Brazil nut