In food web studies, taxonomically unrelated predators are often grouped into trophic levels rega... more In food web studies, taxonomically unrelated predators are often grouped into trophic levels regardless of their relative importance on prey assemblages, multiple predator effects, or interactions such as omnivory. Ants and birds are important predators likely to differentially shape arthropod assemblages, but no studies have compared their effects on a shared prey base. In two separate studies, we excluded birds and ants from branches of a canopy tree (Inga micheliana) in a coffee farm in Mexico for 2 months in the dry and wet seasons of 2002. We investigated changes in arthropod densities with and without predation pressure from (1) birds and (2) ant assemblages dominated by one of two ant species (Azteca instabilis and Camponotus senex). We first analyzed individual effects of each predator (birds, Azteca instabilis, and C. senex) then used a per day effect metric to compare differences in effects across (birds vs ants) and within predator taxa (the two ant species). Individually, birds reduced densities of total and large arthropods and some arthropod orders (e.g., spiders, beetles, roaches) in both seasons. Azteca instabilis did not significantly affect arthropods (total, small, large or specific orders). Camponotus senex, however, tended to remove arthropods (total, small), especially in the dry season, and affected arthropod densities of some orders both positively and negatively. Predators greatly differed in their effects on Inga arthropods (for all, small, large, and individual orders of arthropods) both in sign (±) and magnitudes of effects. Birds had stronger negative effects on arthropods than ants and the two dominant ant species had stronger effects on arthropods in different seasons. Our results show that aggregating taxonomically related and unrelated predators into trophic levels without prior experimental data quantifying the sign and strengths of effects may lead to a misrepresentation of food web interactions.
Conservation biology : the journal of the Society for Conservation Biology, 2010
areas. Vegetatively complex coffee agroecosystems maintain species richness at larger distances f... more areas. Vegetatively complex coffee agroecosystems maintain species richness at larger distances from the forest. Epiphytes colonize canopy trees and provide resources for birds and insects and thus effects of agricultural production on epiphytes may affect other species. We compared diversity, composition, and vertical stratification of epiphytes in a forest fragment and in two coffee farms differing in management intensity in southern Mexico. We also examined spatial distribution of epiphytes with respect to the forest fragment to examine quality of the two agricultural matrix types for epiphyte conservation. We sampled vascular epiphytes in a forest fragment, a shade polyculture farm, and a shade monoculture farm at 100 m, 200 m, and 400 m from the forest. Epiphyte and orchid richness was greater in the forest than in the monoculture but richness was similar in the forest and polyculture farm. Epiphyte species composition differed with habitat type, but not with distance from the forest. In the forest, epiphytes were distributed throughout tree canopies, but in the farms, epiphytes were primarily found on trunks and larger branches. Epiphyte richness and species similarity to forest species declined with distance from the forest fragment in the monoculture, but richness and similarity to forest species did not decline with distance from forest in the polyculture. This suggests polyculture coffee has greater conservation value. In contrast, monoculture coffee is likely a sink habitat for epiphytes dispersing from forests into coffee. Coffee farms differ from forests in terms of the habitat they provide and species composition, thus protecting forest fragments is essential for epiphyte conservation. Nonetheless, in agricultural landscapes, vegetatively complex coffee farms may contribute to conservation of epiphytes more than other agricultural land uses.
In mid-elevation areas of Mesoamerica, Acacia pennatula commonly occurs in mixed woods with vario... more In mid-elevation areas of Mesoamerica, Acacia pennatula commonly occurs in mixed woods with various species of oak. During a 1-y study in Nicaragua, we found the abundance of birds in acacia was far higher than the representation of this species in the mix of trees, whether this is estimated by number of individual trees, canopy cover or foliage cover. This higher abundance was probably related to the fact that acacias supported approximately three to four times the abundance of arthropods that were found in oaks and twice the biomass. Although oak foliage supported fewer arthropods, relatively more of them were large (> 1 cm). The greater preponderance of small arthropods in acacias versus oaks was probably related to the small leaflet size of acacias. However, it is likely that the higher abundance of arthropods in acacias, particularly herbivorous species, was related to the higher nutritional content of the acacia foliage (crude protein, minerals, non-structural carbohydrates) and lower content of digestion-inhibiting compounds (structural carbohydrates, total phenolics, condensed tannins). The major defensive mechanisms of acacia are mechanical (thorns) or qualitative-defence chemicals (cyanogenic glucosides) that are apparently more effective against vertebrate than invertebrate herbivores. These observations support the hypothesis that the anti-herbivore defences of acacia are primarily directed against large mammalian herbivores, rendering the foliage highly palatable to arthropods.
Acacia pennatula groves in mid-elevation valleys of southern Mexico supported both the highest de... more Acacia pennatula groves in mid-elevation valleys of southern Mexico supported both the highest density and diversity of migratory birds compared to other habitats in the region. In addition, we found the highest numbers for over half of the common migratory species. Despite the high degree of leaf loss during the late winter, acacia groves do not experience greater declines in insectivorous migratory bird populations than other local habitats. Color-marked individuals of canopy species had a strong tendency to remain resident within a single acacia grove throughout the winter. Management of native acacias on subtropical rangelands for wood products, fodder, and soil improvement would probably directly and indirectly benefit migratory song bird populations. Neotropical acacia woodland is primarily associated with grazing land for livestock which might discourage some from considering acacia management a viable option for migratory bird conservation. However, acacias were probably widespread in recent geologic time under drier conditions with heavy browsing and seed dispersal by a now extinct megafauna. Two observations suggest a foraging advantage for acacia use: the higher density of migratory birds in acacia is a result of higher numbers of canopy insectivores; and acacias are selected by migrants when they occur in mixed habitat. We hypothesize that plant investment in mechanical defenses (thorns) reduces energy available for chemical defenses effective against insect herbivores.
ABSTRACT Background/Question/Methods Agricultural land-use is a strong driver of biodiversity los... more ABSTRACT Background/Question/Methods Agricultural land-use is a strong driver of biodiversity loss considering that around 40% of the terrestrial land surface is now covered by agriculture. Yet, some agricultural systems can maintain high levels of biodiversity, for example shade coffee plantations can maintain high species diversity. At the same time, maintaining natural habitats in agricultural landscapes can promote biodiversity within farms. Studies are beginning to reveal that different taxonomic groups respond to different factors. We measured the response of tree, spider, ant, parasitoid, bee, leafhopper, and bird biodiversity to variation in local coffee management factors and landscape scale factors in Chiapas, Mexico. In 2011 and 2012, we surveyed 38 sites across 9 plantations for different taxonomic groups and characterized sites for local and landscape factors. We then compared the responses of different taxonomic groups. Results/Conclusions The results suggest that different taxonomic groups respond to different agricultural factors. Spiders responded strongly to elevation, where there were more spiders at lower elevations. Tree canopy connectivity positively influenced both spider abundance and richness. Bird richness had a strong positive correlation with the diversity of habitat types in the surrounding landscape. Local factors were important in explaining tree species richness. Parasitoid, ant, bee, and leafhopper diversity responded to both local and landscape scale factors in contrasting ways. These results suggest that different taxonomic groups respond to different local and landscape coffee agricultural factors. Thus when considering conservation of biodiversity in agriculture, it is important to consider strategies at multiple scales.
Agroecology and conservation must overlap to protect biodiversity and farmer livelihoods. Coffee ... more Agroecology and conservation must overlap to protect biodiversity and farmer livelihoods. Coffee agroecosystems with complex shade canopies protect biodiversity. Yet, few have examined biodiversity in coffee agroecosystems in Asia relative to the Americas and many question whether coffee agroecosystems can play a similar role for conservation. We examined vegetation, ant and bird diversity, coffee yields and revenues, and harvest of alternative products in coffee farms and forests in SW Sumatra, Indonesia near Bukit Barisan Selatan National Park (BBS). BBS is among the last habitats for large mammals in Sumatra and >15,000 families illegally cultivate coffee inside of BBS. As a basis for informing management recommendations, we compared the conservation potential and economic outputs from farms inside and outside of BBS. Forests had higher canopy cover, canopy depth, tree height, epiphyte loads, and more emergent trees than coffee farms. Coffee farms inside BBS had more epiphytes and trees and fewer coffee plants than farms outside BBS. Tree, ant, and bird richness was significantly greater in forests than in coffee farms, and richness did not differ in coffee farms inside and outside of BBS. Species similarity of forest and coffee trees, ants, and birds was generally low (
Theobroma cacao plantings, when managed under the shade of rainforest trees, provide habitat for ... more Theobroma cacao plantings, when managed under the shade of rainforest trees, provide habitat for many resident and migratory bird species. We compared the bird diversity and community structure in organic cacao farms and nearby forest fragments throughout mainland Bocas del Toro, Panama. We used this dataset to ask the following questions: (1) How do bird communities using cacao habitat compare to communities of nearby forest fragments? (2) To what extent do Northern migratory birds use shaded cacao farms, and do communities of resident birds shift their abundances in cacao farms seasonally? (3) Do small scale changes in shade management of cacao farms affect bird diversity? Using fixed radius point counts and additional observations, we recorded 234 landbird species, with 102 species that were observed in both cacao and forest fragments, 86 species that were only observed in cacao farms, and 46 species that were restricted to forest fragments. Cacao farms were rich in canopy and edge species such as tanagers, flycatchers and migratory warblers, but understory insectivores were nearly absent from cacao farms. We observed 27 migratory species, with 18 species in cacao farms only, two species in forest only, and seven species that occurred in both habitats. In cacao farms, the diversity of birds was significantly greater where there was less intensive management of the canopy shade trees. Shade tree species richness was most important for explaining variance in bird diversity. Our study shows that shaded cacao farms in western Panama provide habitat for a wide variety of resident and migratory bird species. Considering current land use trends in the region, we suggest that action must be taken to prevent conversion away from shaded cacao farms to land uses with lower biodiversity conservation value.
Ants limit bird foraging success via interference or exploitative competition. We compared bird f... more Ants limit bird foraging success via interference or exploitative competition. We compared bird foraging (number and duration of visits, bird species visiting) on ant {Azteca instahilis)-infested and ant-free tropical trees {Inga micheliana and Alchornea latifolid). Ants did not affect the number of bird visits or the number of species visiting. Ant presence shortened visit duration (overall and for insectivores) only
In food web studies, taxonomically unrelated predators are often grouped into trophic levels rega... more In food web studies, taxonomically unrelated predators are often grouped into trophic levels regardless of their relative importance on prey assemblages, multiple predator effects, or interactions such as omnivory. Ants and birds are important predators likely to differentially shape arthropod assemblages, but no studies have compared their effects on a shared prey base. In two separate studies, we excluded birds and ants from branches of a canopy tree (Inga micheliana) in a coffee farm in Mexico for 2 months in the dry and wet seasons of 2002. We investigated changes in arthropod densities with and without predation pressure from (1) birds and (2) ant assemblages dominated by one of two ant species (Azteca instabilis and Camponotus senex). We first analyzed individual effects of each predator (birds, Azteca instabilis, and C. senex) then used a per day effect metric to compare differences in effects across (birds vs ants) and within predator taxa (the two ant species). Individually, birds reduced densities of total and large arthropods and some arthropod orders (e.g., spiders, beetles, roaches) in both seasons. Azteca instabilis did not significantly affect arthropods (total, small, large or specific orders). Camponotus senex, however, tended to remove arthropods (total, small), especially in the dry season, and affected arthropod densities of some orders both positively and negatively. Predators greatly differed in their effects on Inga arthropods (for all, small, large, and individual orders of arthropods) both in sign (±) and magnitudes of effects. Birds had stronger negative effects on arthropods than ants and the two dominant ant species had stronger effects on arthropods in different seasons. Our results show that aggregating taxonomically related and unrelated predators into trophic levels without prior experimental data quantifying the sign and strengths of effects may lead to a misrepresentation of food web interactions.
We studied the ecological distribution and foraging behavior of three species in the Black-throat... more We studied the ecological distribution and foraging behavior of three species in the Black-throated Green Warbler (Dendroica virens) species group in the Eastern Highlands of Chiapas, Mexico. The three species, Black-throated Green, Hermit (D. occidentalis) and ...
We surveyed birds in cacao (Theobroma cacao) plantations in the state of Tabasco, Mexico. The sha... more We surveyed birds in cacao (Theobroma cacao) plantations in the state of Tabasco, Mexico. The shade canopy was planted by farmers and consisted of approximately 60 species of trees with no single dominant species. Canopy height averaged 15 m and the structure was multi-storied. We conducted 220 ten minute, 25 m radius point counts for birds and detected 1550 individuals from 81 species. The average number of birds/point and the expected diversity in a fixed number of individuals within the cacao surveyed were well within the range of other lowland habitats, including agricultural sites, that we have surveyed previously in neighbouring Chiapas. In the Tabascan cacao, the migrant group was composed, in part, of forest species, and dimorphic species were represented primarily by males, which in other areas are known to dominate forest or forest-like habitats. In contrast to the composition of migrant species, we found few resident forest specialists in Tabascan cacao. Instead, the tropical resident group was composed of large-bodied generalist species that use small patches of trees in open habitats. These results (moderate diversity, low numbers of forest specialists) differ from the few studies completed in 'rustic' cacao systems located near large tracts of forest. The planted shade cacao agroecosystem -at least in the absence of nearby forest -may have a limited value for conserving lost tropical forest bird diversity, but it provides habitat for woodlandassociated migratory species. Our results also indicate that the planted shade cacao plantations supported few small omnivorous or frugivorous species, probably because cacao itself, as well as the dominant shade trees, produce primarily mammal or wind dispersed fruit and seeds.
® Bird Populations in Rustic and Planted Shade Coffee Plantations of Eastern Chiapas, Mexico Auth... more ® Bird Populations in Rustic and Planted Shade Coffee Plantations of Eastern Chiapas, Mexico Author(s): Russell Greenberg, Peter Bichier, John Sterling Source: Biotropica, Vol. 29, No. 4, (Dec, 1997), pp. 501-514 Published by: The Association for Tropical Biology and ...
Experimental work has established that vertebrates can have a large impact on the abundance of ar... more Experimental work has established that vertebrates can have a large impact on the abundance of arthropods in temperate forest and grasslands, as well as on tropical islands. The importance of vertebrate insectivory has only rarely been evaluated for mainland tropical ecosystems. In this study, we used exclosures to measure the impact of birds on arthropods in Guatemalan coffee plantations. Variation in shade management on coffee farms provides a gradient of similar habitats that vary in the complexity of vegetative structure and floristics. We hypothesized that shaded coffee plantations, which support a higher abundance of insectivorous birds, would experience relatively greater levels of predation than would the sun coffee farms. We found a reduction (64-80%) in the number of large (Ͼ 5 mm in length) but not small arthropods in both coffee types which was consistent across most taxonomic groups and ecological guilds. We also found a small but significant increase in the frequency of herbivore damage on leaves in the exclosures. This level of predation suggests that birds may help in reducing herbivore numbers and is also consistent with food limitation for birds in coffee agroecosystems. However, the presence of shade did not have an effect on levels of insectivory.
We studied the avifauna of sun and shade coffee plantations and associated mid-elevation habitats... more We studied the avifauna of sun and shade coffee plantations and associated mid-elevation habitats during the dry season of 1995. The three plantation types ( Inga , Gliricidia , and sun) showed high faunistic similarities with each other and were both distinct and depauperate compared to matorral and forest patch habitats. Of all the coffee plantation habitats, Inga shade had the highest diversity. Species associated with wooded vegetation were more common in shade plantations, particularly in Inga . A second census showed a decline in bird numbers that was more pronounced in sun and Gliricidia than in Inga plantations. Overall, differences between the plantation types were small and all coffee plantations were less diverse than traditional coffee farms previously studied in nearby Chiapas, México. The relatively low bird diversity was probably due to the low stature, low tree species diversity, and heavy pruning of the canopy. These features reflect management practices that are common throughout Latin America. The most common species of birds in all coffee plantation habitats were common second-growth or edge species; more specialized forest species were almost completely absent from plantations. Furthermore, many common matorral species were rare or absent from coffee plantations, even sun plantations with which matorral shares a similar superficial structure. Coffee plantations probably will only be important for avian diversity if a tall, taxonomically and structurally diverse canopy is maintained. We suggest this is most likely to occur on farms that are managed for a variety of products rather than those designated entirely for the production of coffee.
Coffee agroecosystetns are critical to the success of conservation efforts in Latin America becau... more Coffee agroecosystetns are critical to the success of conservation efforts in Latin America because of their ecological and economic importance. Coffee certification programs may offer one way to protect biodiversity and maintain farmer livelihoods. Established coffee certification programs fall into three distinct, but not mutually exclusive categories: organic, fair trade, and shade. The results of previous studies demonstrate that shade certification can benefit biodiversity, but it remains unclear whether a farmer's participation in any certification program can provide both ecological and economic benefits. To assess the value of coffee certification for conservation efforts in the region, we examined economic and ecological aspects of coffee production for eight coffee cooperatives in Chiapas, Mexico, that were certified organic, certified organic and fair trade, or uncertified. We compared vegetation and ant and bird diversity in coffee farms and forests, and interviewed farmers to determine coffee yield, gross revenue from coffee production, and area in coffee production. Although there are no shade-certified farms in the study region, we used vegetation data to determine whether cooperatives would qualify for shade certification. We found no differences in vegetation characteristics, ant or bird species richness, or fraction of forest fauna in farms based on certification. Farmers with organic and organic and fair-trade certification had more land under cultivation and in some cases higher revenue than uncertified farmers. Coffee production area did not vary among farm types. No cooperative passed shade-coffee certification standards because the plantations lacked vertical stratification, yet vegetation variables for shade certification significantly correlated with ant and bird diversity. Although farmers in the Chiapas highlands with organic and/or fair-trade certification may reap some economic benefits from their certification status, their farms may not protect as much biodiversity as shade-certified farms. Working toward triple certification (organic, fair trade, and shade) at the farm level may enhance biodiversity protection, increase benefits to farmers, and lead to more successful conservation strategies in coffee-growing regions.
Insectivorous birds reduce arthropod abundances and their damage to plants in some, but not all, ... more Insectivorous birds reduce arthropod abundances and their damage to plants in some, but not all, studies where predation by birds has been assessed. The variation in bird effects may be due to characteristics such as plant productivity or quality, habitat complexity, and/or species diversity of predator and prey assemblages. Since agroforestry systems vary in such characteristics, these systems provide a good starting point for understanding when and where we can expect predation by birds to be important. We analyze data from bird exclosure studies in forests and agroforestry systems to ask whether birds consistently reduce their arthropod prey base and whether bird predation differs between forests and agroforestry systems. Further, we focus on agroforestry systems to ask whether the magnitude of bird predation (1) differs between canopy trees and understory plants, (2) differs when migratory birds are present or absent, and (3) correlates with bird abundance and diversity. We found that, across all studies, birds reduce all arthropods, herbivores, carnivores, and plant damage. We observed no difference in the magnitude of bird effects between agroforestry systems and forests despite simplified habitat structure and plant diversity in agroforests. Within agroforestry systems, bird reduction of arthropods was greater in the canopy than the crop layer. Top-down effects of bird predation were especially strong during censuses when migratory birds were present in agroforestry systems. Importantly, the diversity of the predator assemblage correlated with the magnitude of predator effects; where the diversity of birds, especially migratory birds, was greater, birds reduced arthropod densities to a greater extent. We outline potential mechanisms for relationships between bird predator, insect prey, and habitat characteristics, and we suggest future studies using tropical agroforests as a model system to further test these areas of ecological theory.
Coffee agroecosystems with complex shade canopies provide refuges for biodiversity, and reduction... more Coffee agroecosystems with complex shade canopies provide refuges for biodiversity, and reductions in complexity cause biodiversity loss. However, no studies directly compare farms before and after a management shift. We surveyed birds before and after a drastic canopy reduction. We compared abundance and richness of all birds, migrants and residents, and bird guilds, and examined impacts on functional group richness for insect-feeding birds and abundance of two key insectivore groups. Finally, we used confidence inference trees to examine which vegetation variables best explained bird abundance and richness for all birds and different groups. We observed 113 bird species from over 7700 individuals. Surprisingly, there were no changes in cumulative bird richness in the cut and uncut areas; however, bird abundance and mean richness was 3-6 times higher in uncut areas. Abundance and richness of all birds, migrants, residents, and individual guilds was higher in shaded areas, as was functional group richness of insectivores and abundance of key insectivore species. Canopy cover and canopy depth best predicted bird abundance and richness. Birds prey on arthropods including coffee pests. Most coffee farmers eliminate shade trees to increase yields; however, management changes that negatively affect insect-feeding birds may indirectly affect the coffee crop.
It is commonly thought that diverse agroecosystems are less prone to pest outbreaks because they ... more It is commonly thought that diverse agroecosystems are less prone to pest outbreaks because they support a high diversity of natural enemies. The idea that diversity stabilizes functional properties of communities to environmental perturbation is formalized in the ecological literature as the ''insurance hypothesis.'' Recently this hypothesis has been examined theoretically and in microcosm experiments. However it has not been tested empirically in an agroecosystem. Here we provide a test of the insurance hypothesis by examining insect predation by birds in coffee farms with different levels of plant diversity. Lepidopteran larvae were placed in coffee plants, and larval disappearance rates were measured within and outside bird exclosures in two farms with distinct levels of shade. Significant differences were found associated with the exclosure treatment, indicating that birds can potentially prevent pest outbreaks. Furthermore, the effect was significant only for the farm with a high floristic diversity, providing partial evidence in support of the insurance hypothesis.
In food web studies, taxonomically unrelated predators are often grouped into trophic levels rega... more In food web studies, taxonomically unrelated predators are often grouped into trophic levels regardless of their relative importance on prey assemblages, multiple predator effects, or interactions such as omnivory. Ants and birds are important predators likely to differentially shape arthropod assemblages, but no studies have compared their effects on a shared prey base. In two separate studies, we excluded birds and ants from branches of a canopy tree (Inga micheliana) in a coffee farm in Mexico for 2 months in the dry and wet seasons of 2002. We investigated changes in arthropod densities with and without predation pressure from (1) birds and (2) ant assemblages dominated by one of two ant species (Azteca instabilis and Camponotus senex). We first analyzed individual effects of each predator (birds, Azteca instabilis, and C. senex) then used a per day effect metric to compare differences in effects across (birds vs ants) and within predator taxa (the two ant species). Individually, birds reduced densities of total and large arthropods and some arthropod orders (e.g., spiders, beetles, roaches) in both seasons. Azteca instabilis did not significantly affect arthropods (total, small, large or specific orders). Camponotus senex, however, tended to remove arthropods (total, small), especially in the dry season, and affected arthropod densities of some orders both positively and negatively. Predators greatly differed in their effects on Inga arthropods (for all, small, large, and individual orders of arthropods) both in sign (±) and magnitudes of effects. Birds had stronger negative effects on arthropods than ants and the two dominant ant species had stronger effects on arthropods in different seasons. Our results show that aggregating taxonomically related and unrelated predators into trophic levels without prior experimental data quantifying the sign and strengths of effects may lead to a misrepresentation of food web interactions.
Conservation biology : the journal of the Society for Conservation Biology, 2010
areas. Vegetatively complex coffee agroecosystems maintain species richness at larger distances f... more areas. Vegetatively complex coffee agroecosystems maintain species richness at larger distances from the forest. Epiphytes colonize canopy trees and provide resources for birds and insects and thus effects of agricultural production on epiphytes may affect other species. We compared diversity, composition, and vertical stratification of epiphytes in a forest fragment and in two coffee farms differing in management intensity in southern Mexico. We also examined spatial distribution of epiphytes with respect to the forest fragment to examine quality of the two agricultural matrix types for epiphyte conservation. We sampled vascular epiphytes in a forest fragment, a shade polyculture farm, and a shade monoculture farm at 100 m, 200 m, and 400 m from the forest. Epiphyte and orchid richness was greater in the forest than in the monoculture but richness was similar in the forest and polyculture farm. Epiphyte species composition differed with habitat type, but not with distance from the forest. In the forest, epiphytes were distributed throughout tree canopies, but in the farms, epiphytes were primarily found on trunks and larger branches. Epiphyte richness and species similarity to forest species declined with distance from the forest fragment in the monoculture, but richness and similarity to forest species did not decline with distance from forest in the polyculture. This suggests polyculture coffee has greater conservation value. In contrast, monoculture coffee is likely a sink habitat for epiphytes dispersing from forests into coffee. Coffee farms differ from forests in terms of the habitat they provide and species composition, thus protecting forest fragments is essential for epiphyte conservation. Nonetheless, in agricultural landscapes, vegetatively complex coffee farms may contribute to conservation of epiphytes more than other agricultural land uses.
In mid-elevation areas of Mesoamerica, Acacia pennatula commonly occurs in mixed woods with vario... more In mid-elevation areas of Mesoamerica, Acacia pennatula commonly occurs in mixed woods with various species of oak. During a 1-y study in Nicaragua, we found the abundance of birds in acacia was far higher than the representation of this species in the mix of trees, whether this is estimated by number of individual trees, canopy cover or foliage cover. This higher abundance was probably related to the fact that acacias supported approximately three to four times the abundance of arthropods that were found in oaks and twice the biomass. Although oak foliage supported fewer arthropods, relatively more of them were large (> 1 cm). The greater preponderance of small arthropods in acacias versus oaks was probably related to the small leaflet size of acacias. However, it is likely that the higher abundance of arthropods in acacias, particularly herbivorous species, was related to the higher nutritional content of the acacia foliage (crude protein, minerals, non-structural carbohydrates) and lower content of digestion-inhibiting compounds (structural carbohydrates, total phenolics, condensed tannins). The major defensive mechanisms of acacia are mechanical (thorns) or qualitative-defence chemicals (cyanogenic glucosides) that are apparently more effective against vertebrate than invertebrate herbivores. These observations support the hypothesis that the anti-herbivore defences of acacia are primarily directed against large mammalian herbivores, rendering the foliage highly palatable to arthropods.
Acacia pennatula groves in mid-elevation valleys of southern Mexico supported both the highest de... more Acacia pennatula groves in mid-elevation valleys of southern Mexico supported both the highest density and diversity of migratory birds compared to other habitats in the region. In addition, we found the highest numbers for over half of the common migratory species. Despite the high degree of leaf loss during the late winter, acacia groves do not experience greater declines in insectivorous migratory bird populations than other local habitats. Color-marked individuals of canopy species had a strong tendency to remain resident within a single acacia grove throughout the winter. Management of native acacias on subtropical rangelands for wood products, fodder, and soil improvement would probably directly and indirectly benefit migratory song bird populations. Neotropical acacia woodland is primarily associated with grazing land for livestock which might discourage some from considering acacia management a viable option for migratory bird conservation. However, acacias were probably widespread in recent geologic time under drier conditions with heavy browsing and seed dispersal by a now extinct megafauna. Two observations suggest a foraging advantage for acacia use: the higher density of migratory birds in acacia is a result of higher numbers of canopy insectivores; and acacias are selected by migrants when they occur in mixed habitat. We hypothesize that plant investment in mechanical defenses (thorns) reduces energy available for chemical defenses effective against insect herbivores.
ABSTRACT Background/Question/Methods Agricultural land-use is a strong driver of biodiversity los... more ABSTRACT Background/Question/Methods Agricultural land-use is a strong driver of biodiversity loss considering that around 40% of the terrestrial land surface is now covered by agriculture. Yet, some agricultural systems can maintain high levels of biodiversity, for example shade coffee plantations can maintain high species diversity. At the same time, maintaining natural habitats in agricultural landscapes can promote biodiversity within farms. Studies are beginning to reveal that different taxonomic groups respond to different factors. We measured the response of tree, spider, ant, parasitoid, bee, leafhopper, and bird biodiversity to variation in local coffee management factors and landscape scale factors in Chiapas, Mexico. In 2011 and 2012, we surveyed 38 sites across 9 plantations for different taxonomic groups and characterized sites for local and landscape factors. We then compared the responses of different taxonomic groups. Results/Conclusions The results suggest that different taxonomic groups respond to different agricultural factors. Spiders responded strongly to elevation, where there were more spiders at lower elevations. Tree canopy connectivity positively influenced both spider abundance and richness. Bird richness had a strong positive correlation with the diversity of habitat types in the surrounding landscape. Local factors were important in explaining tree species richness. Parasitoid, ant, bee, and leafhopper diversity responded to both local and landscape scale factors in contrasting ways. These results suggest that different taxonomic groups respond to different local and landscape coffee agricultural factors. Thus when considering conservation of biodiversity in agriculture, it is important to consider strategies at multiple scales.
Agroecology and conservation must overlap to protect biodiversity and farmer livelihoods. Coffee ... more Agroecology and conservation must overlap to protect biodiversity and farmer livelihoods. Coffee agroecosystems with complex shade canopies protect biodiversity. Yet, few have examined biodiversity in coffee agroecosystems in Asia relative to the Americas and many question whether coffee agroecosystems can play a similar role for conservation. We examined vegetation, ant and bird diversity, coffee yields and revenues, and harvest of alternative products in coffee farms and forests in SW Sumatra, Indonesia near Bukit Barisan Selatan National Park (BBS). BBS is among the last habitats for large mammals in Sumatra and >15,000 families illegally cultivate coffee inside of BBS. As a basis for informing management recommendations, we compared the conservation potential and economic outputs from farms inside and outside of BBS. Forests had higher canopy cover, canopy depth, tree height, epiphyte loads, and more emergent trees than coffee farms. Coffee farms inside BBS had more epiphytes and trees and fewer coffee plants than farms outside BBS. Tree, ant, and bird richness was significantly greater in forests than in coffee farms, and richness did not differ in coffee farms inside and outside of BBS. Species similarity of forest and coffee trees, ants, and birds was generally low (
Theobroma cacao plantings, when managed under the shade of rainforest trees, provide habitat for ... more Theobroma cacao plantings, when managed under the shade of rainforest trees, provide habitat for many resident and migratory bird species. We compared the bird diversity and community structure in organic cacao farms and nearby forest fragments throughout mainland Bocas del Toro, Panama. We used this dataset to ask the following questions: (1) How do bird communities using cacao habitat compare to communities of nearby forest fragments? (2) To what extent do Northern migratory birds use shaded cacao farms, and do communities of resident birds shift their abundances in cacao farms seasonally? (3) Do small scale changes in shade management of cacao farms affect bird diversity? Using fixed radius point counts and additional observations, we recorded 234 landbird species, with 102 species that were observed in both cacao and forest fragments, 86 species that were only observed in cacao farms, and 46 species that were restricted to forest fragments. Cacao farms were rich in canopy and edge species such as tanagers, flycatchers and migratory warblers, but understory insectivores were nearly absent from cacao farms. We observed 27 migratory species, with 18 species in cacao farms only, two species in forest only, and seven species that occurred in both habitats. In cacao farms, the diversity of birds was significantly greater where there was less intensive management of the canopy shade trees. Shade tree species richness was most important for explaining variance in bird diversity. Our study shows that shaded cacao farms in western Panama provide habitat for a wide variety of resident and migratory bird species. Considering current land use trends in the region, we suggest that action must be taken to prevent conversion away from shaded cacao farms to land uses with lower biodiversity conservation value.
Ants limit bird foraging success via interference or exploitative competition. We compared bird f... more Ants limit bird foraging success via interference or exploitative competition. We compared bird foraging (number and duration of visits, bird species visiting) on ant {Azteca instahilis)-infested and ant-free tropical trees {Inga micheliana and Alchornea latifolid). Ants did not affect the number of bird visits or the number of species visiting. Ant presence shortened visit duration (overall and for insectivores) only
In food web studies, taxonomically unrelated predators are often grouped into trophic levels rega... more In food web studies, taxonomically unrelated predators are often grouped into trophic levels regardless of their relative importance on prey assemblages, multiple predator effects, or interactions such as omnivory. Ants and birds are important predators likely to differentially shape arthropod assemblages, but no studies have compared their effects on a shared prey base. In two separate studies, we excluded birds and ants from branches of a canopy tree (Inga micheliana) in a coffee farm in Mexico for 2 months in the dry and wet seasons of 2002. We investigated changes in arthropod densities with and without predation pressure from (1) birds and (2) ant assemblages dominated by one of two ant species (Azteca instabilis and Camponotus senex). We first analyzed individual effects of each predator (birds, Azteca instabilis, and C. senex) then used a per day effect metric to compare differences in effects across (birds vs ants) and within predator taxa (the two ant species). Individually, birds reduced densities of total and large arthropods and some arthropod orders (e.g., spiders, beetles, roaches) in both seasons. Azteca instabilis did not significantly affect arthropods (total, small, large or specific orders). Camponotus senex, however, tended to remove arthropods (total, small), especially in the dry season, and affected arthropod densities of some orders both positively and negatively. Predators greatly differed in their effects on Inga arthropods (for all, small, large, and individual orders of arthropods) both in sign (±) and magnitudes of effects. Birds had stronger negative effects on arthropods than ants and the two dominant ant species had stronger effects on arthropods in different seasons. Our results show that aggregating taxonomically related and unrelated predators into trophic levels without prior experimental data quantifying the sign and strengths of effects may lead to a misrepresentation of food web interactions.
We studied the ecological distribution and foraging behavior of three species in the Black-throat... more We studied the ecological distribution and foraging behavior of three species in the Black-throated Green Warbler (Dendroica virens) species group in the Eastern Highlands of Chiapas, Mexico. The three species, Black-throated Green, Hermit (D. occidentalis) and ...
We surveyed birds in cacao (Theobroma cacao) plantations in the state of Tabasco, Mexico. The sha... more We surveyed birds in cacao (Theobroma cacao) plantations in the state of Tabasco, Mexico. The shade canopy was planted by farmers and consisted of approximately 60 species of trees with no single dominant species. Canopy height averaged 15 m and the structure was multi-storied. We conducted 220 ten minute, 25 m radius point counts for birds and detected 1550 individuals from 81 species. The average number of birds/point and the expected diversity in a fixed number of individuals within the cacao surveyed were well within the range of other lowland habitats, including agricultural sites, that we have surveyed previously in neighbouring Chiapas. In the Tabascan cacao, the migrant group was composed, in part, of forest species, and dimorphic species were represented primarily by males, which in other areas are known to dominate forest or forest-like habitats. In contrast to the composition of migrant species, we found few resident forest specialists in Tabascan cacao. Instead, the tropical resident group was composed of large-bodied generalist species that use small patches of trees in open habitats. These results (moderate diversity, low numbers of forest specialists) differ from the few studies completed in 'rustic' cacao systems located near large tracts of forest. The planted shade cacao agroecosystem -at least in the absence of nearby forest -may have a limited value for conserving lost tropical forest bird diversity, but it provides habitat for woodlandassociated migratory species. Our results also indicate that the planted shade cacao plantations supported few small omnivorous or frugivorous species, probably because cacao itself, as well as the dominant shade trees, produce primarily mammal or wind dispersed fruit and seeds.
® Bird Populations in Rustic and Planted Shade Coffee Plantations of Eastern Chiapas, Mexico Auth... more ® Bird Populations in Rustic and Planted Shade Coffee Plantations of Eastern Chiapas, Mexico Author(s): Russell Greenberg, Peter Bichier, John Sterling Source: Biotropica, Vol. 29, No. 4, (Dec, 1997), pp. 501-514 Published by: The Association for Tropical Biology and ...
Experimental work has established that vertebrates can have a large impact on the abundance of ar... more Experimental work has established that vertebrates can have a large impact on the abundance of arthropods in temperate forest and grasslands, as well as on tropical islands. The importance of vertebrate insectivory has only rarely been evaluated for mainland tropical ecosystems. In this study, we used exclosures to measure the impact of birds on arthropods in Guatemalan coffee plantations. Variation in shade management on coffee farms provides a gradient of similar habitats that vary in the complexity of vegetative structure and floristics. We hypothesized that shaded coffee plantations, which support a higher abundance of insectivorous birds, would experience relatively greater levels of predation than would the sun coffee farms. We found a reduction (64-80%) in the number of large (Ͼ 5 mm in length) but not small arthropods in both coffee types which was consistent across most taxonomic groups and ecological guilds. We also found a small but significant increase in the frequency of herbivore damage on leaves in the exclosures. This level of predation suggests that birds may help in reducing herbivore numbers and is also consistent with food limitation for birds in coffee agroecosystems. However, the presence of shade did not have an effect on levels of insectivory.
We studied the avifauna of sun and shade coffee plantations and associated mid-elevation habitats... more We studied the avifauna of sun and shade coffee plantations and associated mid-elevation habitats during the dry season of 1995. The three plantation types ( Inga , Gliricidia , and sun) showed high faunistic similarities with each other and were both distinct and depauperate compared to matorral and forest patch habitats. Of all the coffee plantation habitats, Inga shade had the highest diversity. Species associated with wooded vegetation were more common in shade plantations, particularly in Inga . A second census showed a decline in bird numbers that was more pronounced in sun and Gliricidia than in Inga plantations. Overall, differences between the plantation types were small and all coffee plantations were less diverse than traditional coffee farms previously studied in nearby Chiapas, México. The relatively low bird diversity was probably due to the low stature, low tree species diversity, and heavy pruning of the canopy. These features reflect management practices that are common throughout Latin America. The most common species of birds in all coffee plantation habitats were common second-growth or edge species; more specialized forest species were almost completely absent from plantations. Furthermore, many common matorral species were rare or absent from coffee plantations, even sun plantations with which matorral shares a similar superficial structure. Coffee plantations probably will only be important for avian diversity if a tall, taxonomically and structurally diverse canopy is maintained. We suggest this is most likely to occur on farms that are managed for a variety of products rather than those designated entirely for the production of coffee.
Coffee agroecosystetns are critical to the success of conservation efforts in Latin America becau... more Coffee agroecosystetns are critical to the success of conservation efforts in Latin America because of their ecological and economic importance. Coffee certification programs may offer one way to protect biodiversity and maintain farmer livelihoods. Established coffee certification programs fall into three distinct, but not mutually exclusive categories: organic, fair trade, and shade. The results of previous studies demonstrate that shade certification can benefit biodiversity, but it remains unclear whether a farmer's participation in any certification program can provide both ecological and economic benefits. To assess the value of coffee certification for conservation efforts in the region, we examined economic and ecological aspects of coffee production for eight coffee cooperatives in Chiapas, Mexico, that were certified organic, certified organic and fair trade, or uncertified. We compared vegetation and ant and bird diversity in coffee farms and forests, and interviewed farmers to determine coffee yield, gross revenue from coffee production, and area in coffee production. Although there are no shade-certified farms in the study region, we used vegetation data to determine whether cooperatives would qualify for shade certification. We found no differences in vegetation characteristics, ant or bird species richness, or fraction of forest fauna in farms based on certification. Farmers with organic and organic and fair-trade certification had more land under cultivation and in some cases higher revenue than uncertified farmers. Coffee production area did not vary among farm types. No cooperative passed shade-coffee certification standards because the plantations lacked vertical stratification, yet vegetation variables for shade certification significantly correlated with ant and bird diversity. Although farmers in the Chiapas highlands with organic and/or fair-trade certification may reap some economic benefits from their certification status, their farms may not protect as much biodiversity as shade-certified farms. Working toward triple certification (organic, fair trade, and shade) at the farm level may enhance biodiversity protection, increase benefits to farmers, and lead to more successful conservation strategies in coffee-growing regions.
Insectivorous birds reduce arthropod abundances and their damage to plants in some, but not all, ... more Insectivorous birds reduce arthropod abundances and their damage to plants in some, but not all, studies where predation by birds has been assessed. The variation in bird effects may be due to characteristics such as plant productivity or quality, habitat complexity, and/or species diversity of predator and prey assemblages. Since agroforestry systems vary in such characteristics, these systems provide a good starting point for understanding when and where we can expect predation by birds to be important. We analyze data from bird exclosure studies in forests and agroforestry systems to ask whether birds consistently reduce their arthropod prey base and whether bird predation differs between forests and agroforestry systems. Further, we focus on agroforestry systems to ask whether the magnitude of bird predation (1) differs between canopy trees and understory plants, (2) differs when migratory birds are present or absent, and (3) correlates with bird abundance and diversity. We found that, across all studies, birds reduce all arthropods, herbivores, carnivores, and plant damage. We observed no difference in the magnitude of bird effects between agroforestry systems and forests despite simplified habitat structure and plant diversity in agroforests. Within agroforestry systems, bird reduction of arthropods was greater in the canopy than the crop layer. Top-down effects of bird predation were especially strong during censuses when migratory birds were present in agroforestry systems. Importantly, the diversity of the predator assemblage correlated with the magnitude of predator effects; where the diversity of birds, especially migratory birds, was greater, birds reduced arthropod densities to a greater extent. We outline potential mechanisms for relationships between bird predator, insect prey, and habitat characteristics, and we suggest future studies using tropical agroforests as a model system to further test these areas of ecological theory.
Coffee agroecosystems with complex shade canopies provide refuges for biodiversity, and reduction... more Coffee agroecosystems with complex shade canopies provide refuges for biodiversity, and reductions in complexity cause biodiversity loss. However, no studies directly compare farms before and after a management shift. We surveyed birds before and after a drastic canopy reduction. We compared abundance and richness of all birds, migrants and residents, and bird guilds, and examined impacts on functional group richness for insect-feeding birds and abundance of two key insectivore groups. Finally, we used confidence inference trees to examine which vegetation variables best explained bird abundance and richness for all birds and different groups. We observed 113 bird species from over 7700 individuals. Surprisingly, there were no changes in cumulative bird richness in the cut and uncut areas; however, bird abundance and mean richness was 3-6 times higher in uncut areas. Abundance and richness of all birds, migrants, residents, and individual guilds was higher in shaded areas, as was functional group richness of insectivores and abundance of key insectivore species. Canopy cover and canopy depth best predicted bird abundance and richness. Birds prey on arthropods including coffee pests. Most coffee farmers eliminate shade trees to increase yields; however, management changes that negatively affect insect-feeding birds may indirectly affect the coffee crop.
It is commonly thought that diverse agroecosystems are less prone to pest outbreaks because they ... more It is commonly thought that diverse agroecosystems are less prone to pest outbreaks because they support a high diversity of natural enemies. The idea that diversity stabilizes functional properties of communities to environmental perturbation is formalized in the ecological literature as the ''insurance hypothesis.'' Recently this hypothesis has been examined theoretically and in microcosm experiments. However it has not been tested empirically in an agroecosystem. Here we provide a test of the insurance hypothesis by examining insect predation by birds in coffee farms with different levels of plant diversity. Lepidopteran larvae were placed in coffee plants, and larval disappearance rates were measured within and outside bird exclosures in two farms with distinct levels of shade. Significant differences were found associated with the exclosure treatment, indicating that birds can potentially prevent pest outbreaks. Furthermore, the effect was significant only for the farm with a high floristic diversity, providing partial evidence in support of the insurance hypothesis.
Uploads
Papers by Peter Bichier