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San Vito, Costa Rica

Stynoski J.L.,Organization for Tropical Studies | Shelton G.,Harvard University | Stynoski P.,University of Illinois at Urbana - Champaign
Biology Letters | Year: 2014

Parents defend their young in many ways, including provisioning chemical defences. Recent work in a poison frog system offers the first example of an animal that provisions its young with alkaloids after hatching or birth rather than before. But it is not yet known whether maternally derived alkaloids are an effective defence against offspring predators. We identified the predators of Oophaga pumilio tadpoles and conducted laboratory and field choice tests to determine whether predators are deterred by alkaloids in tadpoles. We found that snakes, spiders and beetle larvae are common predators of O. pumilio tadpoles. Snakes were not deterred by alkaloids in tadpoles. However, spiders were less likely to consume mother-fed O. pumilio tadpoles than either alkaloid-free tadpoles of the red-eyed treefrog, Agalychnis callidryas, or alkaloid-free O. pumilio tadpoles that had been hand-fed with A. callidryas eggs. Thus, maternally derived alkaloids reduce the risk of predation for tadpoles, but only against some predators. © 2014 The Author(s).

Norden N.,University of Los Andes, Colombia | Norden N.,University of Connecticut | Norden N.,Pontifical Xavierian University | Letcher S.G.,Organization for Tropical Studies | And 3 more authors.
Ecology | Year: 2012

To gain insight into the ecological processes driving community reassembly in disturbed ecosystems, we assessed the phylogenetic dispersion of early-and late-successional tree species occurring in lowland forests of northeastern Costa Rica. Early-successional species were more closely related than expected by chance, whereas late-successional species tended to be less closely related than expected by chance. Then, we evaluated temporal changes in the phylogenetic structure of seedling and tree assemblages in four 1-ha plots of secondary forests in this region. We found an increase in the phylogenetic evenness among tree individuals over time in all secondary tree assemblages, indicating that relatedness among tree individuals decreases as succession unfolds. This pattern was jointly promoted by recruitment and mortality processes, suggesting that increasing evenness was caused by the replacement of individuals of early-successional species from closely related lineages by late-successional species belonging to a wider diversity of lineages. Based on species occurrence, however, tree community reassembly did not show any significant phylogenetic trend over time. These results suggest that shifts in species abundance over succession have a greater impact on the phylogenetic structure of the community than the turnover of species. Seedling assemblages showed higher phylogenetic evenness than tree assemblages, suggesting that propagule colonization is an important process driving phylogenetic changes in species composition throughout succession. Overall, our findings showed that the phylogenetic structure of these successional communities varies at two temporal scales. At short timescales, decreased dominance by early-successional species over succession leads to increased evenness among tree individuals. At longer timescales, colonization processes result in increased phylogenetic evenness in seedling communities compared to tree communities, forecasting increasing phylogenetic evenness among adult individuals at late-successional stages. © 2012 by the Ecological Society of America.

Reid J.L.,University of California at Santa Cruz | Harris J.B.C.,University of Adelaide | Zahawi R.A.,Organization for Tropical Studies
Biotropica | Year: 2012

An important question for tropical forest restoration is whether degraded lands can be actively managed to attract birds. We censused birds and measured vegetation structure at 27 stations in young (6-9-yr old) actively and passively restored pasture and old growth forest at Las Cruces Biological Station in southern Costa Rica. During 481 10-min point counts, we detected a high diversity-186 species-of birds using the restoration area. Surprisingly, species richness and detection frequency did not differ among habitats, and proportional similarity of bird assemblages to old growth forest did not differ between restoration treatments. Bird detection frequency was instead explained by exotic grass cover and understory stem density-vegetation structures that were not strongly impacted by active restoration. The similarity of bird assemblages in actively and passively restored forest may be attributed to differential habitat preferences within and among feeding guilds, low structural contrast between treatments, or the effect of nucleation from actively restored plots into passively restored areas. Rapid recovery of vegetation in this recently restored site is likely due to its proximity to old growth forest and the lack of barriers to effective seed dispersal. Previous restoration studies in highly binary environments (i.e., open pasture vs. tree plantation) have found strong differences in bird abundance and richness. Our data contradict this trend, and suggest that tropical restoration ecologists should carefully consider: (1) when the benefits of active restoration outweigh the cost of implementation; and (2) which avian guilds should be used to measure restoration success given differential responses to habitat structure. © 2011 by The Association for Tropical Biology and Conservation.

Reid J.L.,University of California at Santa Cruz | Holste E.K.,Michigan State University | Zahawi R.A.,Organization for Tropical Studies
Biological Conservation | Year: 2013

Artificial roosts have been proposed as a tool for augmenting bat populations and catalyzing tropical forest regeneration. In the best case scenario, roosts would attract seed-carrying bats (Family Phyllostomidae) into degraded pastures and form nucleating patches of native vegetation. We tested this scenario by monitoring 48 artificial roosts in pastures and adjacent forest fragments in southern Costa Rica over 2. years. Half of the pasture roosts were exposed to direct sunlight and half were affixed to 4-m living stakes of Erythrina poeppigiana (Walp.) O.F. Cook that provided shade. After 2. years, 94% of roosts in forest and 40% of roosts in pasture had been used by bats at least once - primarily for nocturnal feeding. Maximum daily temperature inside of roosts was the best microclimatic predictor of bat visitation. We identified at least five species of bats that visited roosts, including two frugivores (Carollia and Glossophaga spp.). Bat-mediated seed dispersal increased with the number of frugivorous bat detections at roosts, but seedling recruitment did not increase with either bat detections or seed abundance over a 2-year period. Given that bats rarely used roosts in pastures, and bat visitation did not increase seedling recruitment, our data suggest that artificial bat roosts did not accelerate forest regeneration in abandoned, premontane pastures in southern Costa Rica. This method could be refined by investigating alternative roost designs, barriers to seedling recruitment below roosts, improvement of roost microclimatic conditions in pastures, and ability of bats to detect roosts in different habitats. © 2013 Elsevier Ltd.

Mendenhall C.D.,Stanford University | Archer H.M.,San Francisco State University | Archer H.M.,University of Colorado at Boulder | Brenes F.O.,Organization for Tropical Studies | And 2 more authors.
Conservation Letters | Year: 2013

Debate over balancing agricultural production and biodiversity conservation has generated two opposing strategies: a "land sparing" approach involving large-scale nature reserves, versus a "land sharing" approach where agricultural areas support wildlife through fine-scale conservation. As a result of this debate, studies focus almost exclusively on species diversity and food production, while ignoring other critical ecosystem processes such as disease dynamics. Here we quantify how tropical avian malaria in an abundant sedentary bird species responds at fine spatial scales in a "land sharing" system. We find the proportion and configuration of countryside forest elements within a radius of 400 m, proximity to the nearest river, and habitat type explains malaria prevalence across the region. We simulate "land sparing" and "land sharing" land use strategies and model malaria prevalence to find that land sharing mitigates malaria prevalence more effectively. With these analyses, we gain a better understanding of how biodiversity, ecosystem services, agricultural yield, and human well-being intersect in complex ecosystems. ©2012 Wiley Periodicals, Inc.

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