The Competitive Structure of Communities: An Experimental Approach with Protozoa

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/119089/1/ecy1969503362.pd

On the Covariance of the Community Matrix

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/119085/1/ecy1972531187.pd

Biodiversity Conservation in Tropical Agroecosystems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74765/1/annals.1439.011.pd

On the resolution of chaos in population models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23901/1/0000144.pd

Choosing category size in a stage projection matrix

A basic problem associated with choosing category size in a stage projection matrix is described. “Errors of estimation” are large if the category size is chosen too small and “errors of distribution” are large if the category size is chosen too large. An approximate technique of balancing these two error types is suggested as a solution to this dilemma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47719/1/442_2004_Article_BF00344691.pd

Maximizing crop yield in alley crops

A simple graphical model is presented illustrating the balance between facilitation and competition necessary for maximizing crop yield in alley cropping systems. Three functions are composed into the decision function: (1) the percent increase in crop yield from facilitation resulting from prunings, (2) the amount of prunings resulting from different tree densities, and (3) the percent reduction in crop yield from competition from trees. The resulting function illustrates how the balance between facilitation and competition may provide a window of opportunity for the beneficial use of alley crops.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41765/1/10457_2004_Article_164135.pd

On the regional stabilization of locally unstable predator-prey relationships

The stabilizing effects of interhabitat migration and local population extinction are established by an analysis of the variable Pi, where Pi refers to the proportion of habitats occupied by species i. This is followed by an analysis of the qualitative nature of changes in regional and local factors and their influence on establishing stable or unstable conditions. It is seen that the appropriate balance between interhabitat migration and local population extinction is capable of stabilizing an otherwise unstable predator-prey interaction in a wide variety of situations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33812/1/0000068.pd

Post-Agricultural Succession in El PetÉn, Guatemala

We compared post-agricultural succession across the range of farming activities practiced in Guatemala's northern lowlands: agroforestry, swidden, ranching, and input-intensive monocultures. At 10 sites over 13 to 40 months we assessed the following characteristics of trees and shrubs that were>1 cm diameter at breast height: height, basal-area accumulation, recruitment of all individuals and fleshy-fruited individuals, and accumulation of all species and fleshy-fruited species. Succession, as measured by all these response variables except height, was dramatically faster on agroforestry and swidden sites than on pastures or input-intensive monocultures. Overall recruitment was faster for swiddens than for agroforests, but other response variables did not differ significantly between the two treatments. Regression results suggest that initial ground cover by herbs inhibited recruitment of woody colonists. The significant positive coefficient for initial basal area and the significant negative coefficient for distance from forest for accumulation of both fleshy-fruited individuals and species are probably explained by the behavioral responses of seed-dispersing animals. Our results suggest that the conservation strategy of discouraging swidden agriculture in favor of sedentary, input-intensive agriculture to relieve pressure on old-growth forest may be counterproductive over the long term.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75095/1/j.1523-1739.2003.01265.x.pd

Effects of Management Intensity and Season on Arboreal Ant Diversity and Abundance in Coffee Agroecosystems

Agricultural intensification decreases arthropod predator diversity, abundance and population stability, and may affect interactions between top predators and their arthropod prey – ultimately affecting ecosystem services. Coffee management intensification (reduction or removal of shade trees) reduces diversity of arthropod predators (ground-foraging ants). Because ants provide ecosystem services by controlling pests, influences of intensification on arboreal, coffee-foraging ant diversity and abundance are important. We here address how coffee intensification affects: (1) coffee-foraging ant diversity and abundance and (2) seasonal fluctuations in ant abundance. In each of four coffee sites of varying management intensity in Chiapas, Mexico, we sampled vegetation and using two methods, sampled ant diversity and abundance over two years. Sites significantly differed in vegetation and management intensity. Coffee-foraging ant diversity generally decreased with increasing management intensity (16–26% fewer species observed in the most intensively-managed site). Ant abundance was higher in the wet season. Management intensity, however, did not influence ant abundance or seasonal fluctuations in abundance. Our results highlight the importance of diverse agricultural systems in maintaining arthropod predator diversity, and point to one model system in which we may effectively test how diversity per se affects ecosystem services.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42427/1/10531_2004_Article_4247.pd

Conservation of biodiversity in coffee agroecosystems: a tri-taxa comparison in southern Mexico

We compare species richness of birds, fruit-feeding butterflies and ground-foraging ants along a coffee intensification gradient represented by a reduction in the number of species of shade trees and percentage of shade cover in coffee plantations. We sampled the three taxa in the same plots within the same period of time. Two sites were selected in the Soconusco region of the state of Chiapas, Mexico. Within each site four habitat types were selected and within each habitat type four points were randomly selected. The habitat types were forest, rustic coffee, diverse shade coffee, and intensive coffee (low density of shade). We found different responses of the three taxa along the intensification gradient. While ants and butterflies generally decrease in species richness with the decrease of shade cover, birds declined in one site but increased in the other. Ant species richness appears to be more resistant to habitat modification, while butterfly species richness appears to be more sensitive. Bird species richness was correlated with distance from forest fragments but not with habitat type, suggesting that scale and landscape structure may be important for more mobile taxa. For each of these taxa, the rustic plantation was the one that maintained species richness most similar to the forest. We found no correlation between the three taxa, suggesting that none of these taxa are good candidates as surrogates for each other. We discuss the implications of these results for the conservation of biodiversity in coffee plantations, in particular, the importance of distinguishing between different levels of shade, and the possibility that different taxa might be responding to habitat changes at different spatial scales.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42405/1/10531_2004_Article_5096977.pd