Insights from excrement: invasive gastropods shift diet to consume the coffee leaf rust and its mycoparasite

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154946/1/ecy2966.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154946/2/ecy2966_am.pd

The Community Ecology of Herbivore Regulation in an Agroecosystem: Lessons from Complex Systems

AbstractWhether an ecological community is controlled from above or below remains a popular framework that continues generating interesting research questions and takes on especially important meaning in agroecosystems. We describe the regulation from above of three coffee herbivores, a leaf herbivore (the green coffee scale, Coccus viridis), a seed predator (the coffee berry borer, Hypothenemus hampei), and a plant pathogen (the coffee rust disease, caused by Hemelia vastatrix) by various natural enemies, emphasizing the remarkable complexity involved. We emphasize the intersection of this classical question of ecology with the burgeoning field of complex systems, including references to chaos, critical transitions, hysteresis, basin or boundary collision, and spatial self-organization, all aimed at the applied question of pest control in the coffee agroecosystem

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies

Emergent Spatial Heterogeneity Structures the Assembly and Functioning of Ecological Communities: An Agroecological Perspective

Heterogeneity is a ubiquitous feature of ecosystems and perhaps an important contributing factor to the oft noted difficulties associated with making generalizations in community ecology. Our answers to questions regarding the origins and consequences of various types of heterogeneity in ecological systems have long been met with contingencies and context dependency, highlighting the need to continually revisit our organizing metaphors. The work presented in this dissertation is concerned with these metaphors and especially those associated with the ecological processes that generate spatial heterogeneity in ecosystems. In eleven case studies, we attempt to understand the generation and subsequent implications of spatial heterogeneity for the assembly and functioning of ecological communities in agroecosystems. We first address how ecological interactions create spatial pattern in Chapter 1 by presenting a novel demographic framework for understanding consumer-resource generated spatial patterns. We then explore how spatial heterogeneity influences ecological interactions in Chapter 2 and Chapter 3. Whereas in the former we ask how basic ecological interactions are influenced by dynamic patterns of heterogeneity in ecosystems, in the later we ask how changes in spatial structure influences pathogen epidemics. Chapter 4 then empirically explores how dispersal differentially alters community structure in leaf-litter metacommunities and Chapter 5 explores the use of coupled oscillators as a metaphor for ecological communities. These first five chapters represent an attempt to understand the feedbacks between ecological interactions that create spatial heterogeneity and how spatial heterogeneity structures ecological communities. The dissertation then shifts focus to a fungal pathogen of coffee, the coffee leaf rust, and uses its community of consumers as a model system to understand how spatial heterogeneity influences community structure and how community structure influences biological control of the pathogen. Chapter 6 gives a brief overview of the history and ecology of the pathogen and its community, and Chapters 7-9 explore the assembly and organization of these communities, highlighting their interactions with the pathogen as well as among themselves. Finally, Chapters 10 and 11 are concerned with the structure of interaction networks associated with the coffee leaf rust and the provisioning of top-down control of the coffee leaf rust pathogen in both Mexico and Puerto Rico. Taken together, this dissertation contributes to our understanding of how ecological communities create and are impacted by the heterogeneous environments they occupy. Furthermore, this work attempts to highlight the importance of such concepts in an agroecological context where questions of community structure and population regulation have the potential for practical significance.PHDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/175651/1/zhajianf_1.pd

Changes in species diversity of arboreal spiders in Mexican coffee agroecosystems: untangling the web of local and landscape influences driving diversity

Agricultural intensification is implicated as a major driver of global biodiversity loss. Local management and landscape scale factors both influence biodiversity in agricultural systems, but there are relatively few studies to date looking at how local and landscape scales influence biodiversity in tropical agroecosystems. Understanding what drives the diversity of groups of organisms such as spiders is important from a pragmatic point of view because of the important biocontrol services they offer to agriculture. Spiders in coffee are somewhat enigmatic because of their positive or lack of response to agricultural intensification. In this study, we provide the first analysis, to our knowledge, of the arboreal spiders in the shade trees of coffee plantations. In the Soconusco region of Chiapas, Mexico we sampled across 38 sites on 9 coffee plantations. Tree and canopy connectedness were found to positively influence overall arboreal spider richness and abundance. We found that different functional groups of spiders are responding to different local and landscape factors, but overall elevation was most important variable influencing arboreal spider diversity. Our study has practical management applications that suggest having shade grown coffee offers more suitable habitat for arboreal spiders due to a variety of the characteristics of the shade trees. Our results which show consistently more diverse arboreal spider communities in lower elevations are important in light of looming global climate change. As the range of suitable elevations for coffee cultivation shrinks promoting arboreal spider diversity will be important in sustaining the viability of coffee

High intermediary mutualist density provides consistent biological control in a tripartite mutualism

Understanding the ecology of mutualisms becomes a particularly important task when considering agroecosystems, as many ecosystem services are associated with mutualistic interactions. Here we report on experiments associated with an indirect pest control mutualism between the arboreal nesting ant Azteca sericeasur and coffee. This system is particularly interesting because the indirect Azteca-Coffea mutualism emerges from an Azteca-scale insect mutualism that takes place on the coffee plant. We describe this interaction structure as a mutualism-dependent mutualism and ask whether the density of intermediary mutualist (scale insects, Coccus) that benefits Azteca also influences the benefits provided to coffee plants. We found that indeed Azteca’s benefit to Coffea is consistent when Coccus density is high. Furthermore, we also found that at low Coccus density Azteca only benefits Coffea in the beginning of the rainy season, and this effect is likely due to the fact that Coccus produces less sugars with higher precipitation. We suggest a framework for thinking about context-dependency in agroecosystem mutualisms that may provide a more mechanistic way to tease apart the prevalent context-dependent results in ecological literature. Finally, we address some past recommendations as it pertains to the management of the Azteca-Coffea-Coccus complex in coffee agroecosystems

Mexico's Ants: Who are They and Where do They Live?

International audienc