Effect of landscape tree cover, sex and season on the bioaccumulation of persistent organochlorine pesticides in fruit bats of riparian corridors in eastern Mexico.

Riparian forests are recognized as important ecosystems for biodiversity conservation in transformed landscapes. Many animal species that use this type of vegetation facilitate its recovery through pollination and seed dispersal. In landscapes dominated by agrosystems and cattle ranching, persistent organochlorine pesticides (OCPs) in the riparian system may have an effect on the physiology and fitness of animals. In this study, we measured bioaccumulation of OCPs in the most abundant frugivorous bat, Sturnira hondurensis, from the upper part of La Antigua basin, Veracruz, Mexico and, from these data, estimated accumulation by the frugivorous bat community of riparian forests in contrasting, transformed (TL) and forested (FL) landscapes. Concentration of ΣDDT, Σdrines, Σclordano, ΣHCH, Σheptachlor and Σendosulfan was measured by gas-chromatography in 23 female and 33 male adult Sturnira captured during the dry and rainy seasons. Using censored data statistics, we found that the sex of the individual was significant for ΣHCH, and that interactions of landscape type (TL vs. FL) and season (dry vs. wet), and sex and season were significant for Σendosulfan and Σdrines, respectively. Mean ΣDDT (6.86 µg/g) and ΣHCH (28.22 µg/g) concentrations were lower than those reported for frugivorous bats in India but concentrations of Σdrines (13.86 µg/g) were higher than those reported in insectivorous bats. In our study sites, frugivorous bats are bioaccumulating higher amounts of OCPs in TL than in FL. We discuss the potential of this species as a bio-indicator of OCPs contamination in river basins.

Bat-fruit interactions are more specialized in shaded-coffee plantations than in tropical mountain cloud forest fragments.

Forest disturbance causes specialization of plant-frugivore networks and jeopardizes mutualistic interactions through reduction of ecological redundancy. To evaluate how simplification of a forest into an agroecosystem affects plant-disperser mutualistic interactions, we compared bat-fruit interaction indexes of specialization in tropical montane cloud forest fragments (TMCF) and shaded-coffee plantations (SCP). Bat-fruit interactions were surveyed by collection of bat fecal samples. Bat-fruit interactions were more specialized in SCP (mean H2 ' = 0.55) compared to TMCF fragments (mean H2 ' = 0.27), and were negatively correlated to bat abundance in SCP (R = -0.35). The number of shared plant species was higher in the TMCF fragments (mean = 1) compared to the SCP (mean = 0.51) and this was positively correlated to the abundance of frugivorous bats (R= 0.79). The higher specialization in SCP could be explained by lower bat abundance and lower diet overlap among bats. Coffee farmers and conservation policy makers must increase the proportion of land assigned to TMCF within agroecosystem landscapes in order to conserve frugivorous bats and their invaluable seed dispersal service.

Specialization clines in the pollination systems of agaves (Agavaceae) and columnar cacti (Cactaceae): A phylogenetically controlled meta-analysis.

The biogeography of plant-animal interactions is a novel topic on which many disciplines converge (e.g., reproductive biology, biogeography, and evolutionary biology). Narrative reviews have indicated that tropical columnar cacti and agaves have highly specialized pollination systems, while extratropical species have generalized systems. However, this dichotomy has never been quantitatively tested. We tested this hypothesis using traditional and phylogenetically informed meta-analysis. Three effect sizes were estimated from the literature: diurnal, nocturnal, and hand cross-pollination (an indicator of pollen limitation). Columnar cactus pollination systems ranged from purely bat-pollinated in the tropics to generalized pollination, with diurnal visitors as effective as nocturnal visitors in extratropical regions; even when phylogenetic relatedness among species is taken into account. Metaregressions identified a latitudinal increase in pollen limitation in columnar cacti, but this increase was not significant after correcting for phylogeny. The currently available data for agaves do not support any latitudinal trend. Nectar production of columnar cacti varied with latitude. Although this variation is positively correlated with pollination by diurnal visitors, it is influenced by phylogeny. The degree of specificity in the pollination systems of columnar cacti is heavily influenced by ecological factors and has a predictable geographic pattern.

Nurse plants vs. nurse objects: effects of woody plants and rocky cavities on the recruitment of the Pilosocereus leucocephalus columnar cactus.

BACKGROUND AND AIMS: Most studies on cactus recruitment have focused on the role of woody plants as seedling facilitators. Although the spatial association of cacti with objects had been described, the mechanisms underlying this association remain unknown. The aims of this study were to identify which mechanisms facilitate the establishment of a columnar cactus under the shade and protection of objects and to compare these mechanisms with those involved in plant-plant facilitation. METHODS: Three split-split-plot field experiments were conducted to compare the effects of two microhabitats (inside rocky cavities and beneath plant canopies) on seed removal, germination, seedling survivorship and dry weight. Flat, open spaces were used as the control. For each microhabitat, the effect of seed or seedling protection and substrate limitation were explored; aboveground microclimate and some soil properties were also characterized. KEY RESULTS: The permanence of superficial seeds was greater inside rocky cavities than beneath woody plant canopies or on flat, open areas. Germination was similar in cavities and beneath plant canopies, but significantly higher than on flat, open areas. Seedling survivorship was greater beneath plant canopies than inside cavities or on flat, open spaces. CONCLUSIONS: The mechanisms of plant facilitation are different from those of object facilitation. There are seed-seedling conflicts involved in the recruitment of P. leucocephalus: nurse plants favour mainly seedling survivorship by providing a suitable microenvironment, while nurse objects mainly favour seed permanence, by protecting them from predators.

Bat- and Bird-Generated Seed Rains at Isolated Trees in Pastures in a Tropical Rainforest.

Bats are abundant and effective seed dispersers inside the forest, but what happens when a forest is fragmented and transformed into pasture? The landscape at Los Tuxtlas, Mexico, originally rainforest, is greatly fragmented and covered with pastures. We analyzed the seed rains produced by frugivorous bats and birds under isolated trees in pastures in the fragmented landscape and the contribution of this process to vegetational recovery. We surveyed bats and obtained fecal samples under isolated trees in pastures. We also collected seed rain below the canopy of 10 isolated Ficus trees, separating nocturnally dispersed seeds from diurnally dispersed seeds. We caught 652 bats of 20 species; 83% of captures were frugivores. The most abundant species were Sturnira lilium (48%), Artibeus jamaicensis (18%), Carollia perspicillata (12%), and Dermanura tolteca (11%). Fecal samples contained seeds of 19 species in several families: Piperaceae (50%), Moraceae (25%), Solanaceae (12%), Cecropiaceae (10%), and others (3%). Sturnira lilium was the most important disperser bat in pastures. Seed rain was dominated by zoochorous species (89%). We found seed diversity between day and night seed captures to be comparable, but we found a significant interaction of disperser type ( bird or bat) with season. Seven plant species accounted for 79% of the seed rain: Piper auritum (23%), Ficus ( hemiepiphytic-strangler tree) spp. (17%), Cecropia obtusifolia (10%), P. amalago (10%), Ficus ( free-standing tree) spp. (8%), P. yzabalanum (6%), and Solanum rudepanum (5%). Bats and birds are important seed dispersers in pastures because they disperse seeds of pioneer and primary species (trees, shrubs, herbs, and epiphytes), connect forest fragments, and maintain plant diversity. Consequently, they might contribute to the recovery of woody vegetation in disturbed areas in tropical humid forests.

RESUMEN: Los murciélagos son abundantes y efectivos dispersores de semillas en la selva húmeda alta. Pero, ¿qué sucede cuando la selva es fragmentada y convertida en pastizales? El paisaje en Los Tuxtlas, México, cuya vegetación original era la de bosque lluvioso, está fuertemente fragmentado y dominado por pastizales. Analizamos la lluvia de semillas producida por murciélagos y aves frugívoras bajo árboles aislados en pastizales del paisaje fragmentado, y la contribución de este proceso a la recuperación de la vegetación. Capturamos murciélagos y obtuvimos muestras fecales bajo árboles aislados en pastizales. Colectamos la lluvia de semillas bajo 10 Ficus aislados, separando las semillas "nocturnas" de las "diurnas." Capturamos 652 murciélagos de 20 especies, el 83% de ellos fueron frugívoros. Las especies dominantes fueron: Sturnira lilium (48%), Artibeus jamaicensis (18%), Carollia perspicillata (12%), y Dermanura tolteca (11%). Las muestras fecales contenían semillas de 19 especies de varias familias: Piperaceae (50%), Moraceae (25%), Solanacea (12%), Cecropiaceae (10%), y otras (3%). Sturnira lilium resultó ser el murciélago dispersor más importante del pastizal. En la lluvia de semillas el 89% de las especies fueron zoócoras. No se encontró diferencia en la diversidad de semillas depositadas en la noche o en el día; sin embargo, hubo una interacción significativa del tipo de dispersor (ave o murciélago) con la época del año. Siete especies dominaron el 79% del total de la lluvia: Piper auritum (23%), Ficus ( hemiepífito-matapalo; 17%), Cecropia obtusifolia (10%), P. amalago (10%), Ficus (terrestre; 8%), P. yzabalanum (6%) y Solanum rudepanum (5%). Los murciélagos y las aves son importantes dispersores en pastizales ya que dispersan semillas de especies pioneras y primarias (árboles, arbustos, hierbas y epífitas); conectan remanentes de selva y mantienen la diversidad vegetal. Consecuentemente pueden promover la recuperación de la vegetación leñosa en áreas perturbadas de regiones tropicales húmedas.