The Complex Responses of Social Stingless Bees (Apidae: Meliponini) to Tropical Deforestation
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Forest Ecology and Management 258 (2009) 1830–1837 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco The complex responses of social stingless bees (Apidae: Meliponini) to tropical deforestation Berry J. Brosi * Department of Biology, Stanford University, 385 Serra Mall, Stanford, CA 94305, USA ARTICLE INFO ABSTRACT Article history: Despite concern over a putative ‘‘global pollination crisis’’, we still have an incomplete understanding of Received 26 November 2008 how bee communities respond to land-use change. I studied the responses of social stingless (or Received in revised form 22 February 2009 ‘‘meliponine’’) bees (Hymenoptera: Apidae: Meliponini) to surrounding forest cover and floral resources Accepted 25 February 2009 in 35 sites in a largely deforested landscape in Costa Rica over three years, sampling bees with a standardized netting protocol. I recorded a diverse fauna of meliponines, comprised of 20 species and Keywords: nine genera. I found that meliponine species richness and abundance are strongly related to forest cover, Pollinator but not floral resource variables (blooming plant species richness and abundance). The effect of forest on Land-use change meliponine abundance, but not diversity, disappeared when the most common meliponine species, Deforestation Bee communities Trigona fulviventris (which comprised 45% of sampled individuals), was excluded from analyses. Biodiversity Meliponine community composition, by contrast, was related most strongly to plant species richness, only weakly to forest cover, and not related to blooming plant abundance. This work differs from past work in the same landscape, which did not find evidence of changes in species richness or abundance of meliponines and forest-related variables (distance to forest or forest fragment size), but did find shifts toward meliponine-dominated communities near forests, especially larger ones. The larger true sample size (i.e. number of sample sites) of the present work likely improved the statistical power to detect these relationships. While meliponines are forest dependent, I recorded some species in the smallest forest fragments in the landscape, and as a group they respond strongly to overall forest cover in the landscape (i.e. including both small and large patches of forest). Both of these observations support arguments for preserving even small fragments of forest in agricultural landscapes. Given the ecological and economic importance of meliponine bees, it is imperative that we better understand their long-term conservation needs in the changing tropical landscapes of the world. ß 2009 Elsevier B.V. All rights reserved. 1. Introduction 1992). All meliponine bees are eusocial, with perennial hives consisting of a single queen and thousands of workers. Meliponine Despite ongoing controversy over pollinator declines and a workers recruit foragers to rich sources of floral forage, thus concomitant increase in studies on the effects of anthropogenic allowing them to efficiently pollinate tropical plants whose environmental change on pollinators (e.g. Ghazoul, 2005; Steffan- blooming period is brief, including crops such as coffee (Klein Dewenter et al., 2005), we still do not have a comprehensive view et al., 2003a; Ricketts, 2004). This efficient exploitation of floral of how bee communities respond to land use change. This problem resources, along with their high densities, means that they are also is particularly acute in the tropics, where most tropical forest trees major players in the cycling of nutrients in tropical forests (Roubik, are animal-pollinated (Bawa, 1990), where pollination limitation is 1989: p. 354). most severe (Vamosi et al., 2006) and where land-use change is the This importance carries over to the human enterprise as well, largest driver of biodiversity loss (Sala et al., 2000). since meliponines contribute to the pollination of >60 tropical The meliponine, or social stingless, bees (Apidae: Meliponini) crops. They are the primary wild pollinators of coffee (Klein et al., are a critically important group of tropical bees. They are the most 2003b); and contribute to the effective pollination of avocado, diverse group of eusocial tropical bees (Michener, 2000: p. 779), sweet pepper, tomato, cucumber, strawberry, and rambutan (Slaa and may be the most abundant clade of bees on earth (Roubik, et al., 2006); as well as coconut, mango, macadamia nuts, chayote, carambola (‘‘star fruit’’), and achiote (Heard, 1999) among many other crops. These meliponine-mediated pollination services likely * Tel.: +1 650 450 3715; fax: +1 650 723 5920. contribute billions of dollars to tropical economies ever year E-mail address: [email protected]. (Kearns et al., 1998; Ricketts et al., 2004b; Klein et al., 2007). The 0378-1127/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2009.02.025 B.J. Brosi / Forest Ecology and Management 258 (2009) 1830–1837 1831 importance of meliponines as pollinators of tropical crops is likely bees (Brosi et al., 2007, 2008). With data from both studies and to increase given the ongoing problems of honey bees, including with restrictions I imposed on sites (detailed below), I used 35 sites Africanization (Schneider et al., 2004) and parasites and disease in the Las Cruces landscape in this analysis. The results presented (e.g. Oldroyd, 2007). here are distinct from those in Brosi et al. (2007, 2008) in that While the Maya and other indigenous peoples have managed analyses combine both datasets (though only including sites that meliponine bees for millennia (Chemas and Rico-Gray, 1991), and were sampled in a minimum of two full field seasons), along with some efforts have been made to modernize techniques and several new analyses. The sites used in Brosi et al. (2007) fell along promote the husbandry of meliponines, also known as ‘‘melipo- a gradient of distance to forest and were sampled in the rainy niculture’’ (Cortopassi-Laurino et al., 2006), wild colonies account season (July-September) of 2003 and in the dry season (February- for the vast majority of crop pollination activities that are May) of 2005. The sites from Brosi et al. (2008) were along a conducted by meliponines. Thus, nearly all meliponine pollination gradient of forest fragment size, with sample sites situated in activity can be considered a true ecosystem service, rather than a pastures at the edges of the forest fragments. These sites were managed human activity. sampled in the rainy season (June-September) of 2004, and the dry Given the central place of meliponine bees in provisioning season (February–May) of 2005, with the dry season samples being tropical crop pollination services, it is critically important to taken concurrently with those from Brosi et al. (2007). Sites ranged understand how they respond to ongoing land-use changes. This from 500 m to 13 km in geographic distance from one another and is particularly true given that studies of bee communities in Central from 900 to 1300 m in elevation above sea level. America and Southeast Asia have found that meliponine bees are strongly associated with native forest habitat (Klein et al., 2002; 2.3. Bee and plant sampling Ricketts, 2004; Brosi et al., 2007; Brosi et al., 2008). On one hand, this association with forest is not surprising given that many (but not all) In each site, two field team members netted bees in a meliponines are tree-cavity nesters that may rely on tropical forests 20 m  20 m square plot for a 15-minute period, focusing their for nesting habitats (Roubik, 1989). On the other hand, many efforts on flowering plants within the plot. The netting team caught meliponine species will forage and even nest in human-dominated bees in the order that they were seen, and thus would not pursue a habitats that have experienced high degrees of deforestation (Klein relatively rare species at the expense of a common species seen et al., 2002; Ricketts, 2004; Brosi et al., 2007, 2008). first. The netting trials were focused across all bees in the bee This tendency of meliponines to forage in human-dominated community; in the analyses presented here, we include only the habitats is a positive attribute when considering crop pollination— meliponine bees from these samples. We did not net bees in and also makes for a direct linkage between forest cover and conditions of fog, precipitation, or high winds. For more on the meliponine-mediated crop pollination. For example, Ricketts et al. sampling, see Brosi et al. (2007, 2008). Specimens were pinned, (2004a) found that two patches of tropical forest near a large coffee labeled, and identified to species using Roubik (1992). V. Gonzalez farm in southern Costa Rica supported meliponine bees which and I. Hinojosa, University of Kansas, evaluated and corrected contributed approximately $60,000 a year to the value of the coffee species determinations. Specimens are housed in the Biology harvest, through increases in both the quantity and quality of Department, Stanford University. coffee beans produced. Blooming plants were counted along 5 parallel 20 m transects In order to improve understanding the responses of meliponine in each site, counting and identifying all plants in bloom within bees to land use change, I sampled meliponines over 3 years in a 50 cm of either side of the transect line. See Brosi et al. (2007, 2008) largely deforested landscape in southern Costa Rica, along for more details on plant sampling. gradients of both distance to forest and also forest fragment size. I hypothesized that meliponines would be more diverse and 2.4. Data analysis abundant in sites with more forest cover surrounding them, and in sites with greater density and diversity of floral resources. I also I analyzed two responses (dependent variables) of meliponine hypothesized that meliponine species would respond differently to communities to landscape structure and plant resource avail- land use change, and that these differences would be reflected in ability: (1) the species richness and abundance of meliponines measures of community composition.