Organization for Tropical Studies

San Vito, Costa Rica

Organization for Tropical Studies

San Vito, Costa Rica
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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.

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.

Coetzee B.W.T.,Organization for Tropical Studies | Coetzee B.W.T.,University of Witwatersrand
Biodiversity and Conservation | Year: 2016

While protected areas are a key component of the global conservation strategy, quantitative demonstrations of their positive ecological performance, meaning the extent to which they conserve the biodiversity features they were designated for, is broadly lacking. This commentary presents the emerging field of impact of evaluation of protected areas, with a focus on establishing their ecological performance. It highlights recent advances in protected area evaluations and explores the challenges remaining in developing a more credible evidence base to demonstrate the biodiversity conservation benefits of protected areas. © 2016 Springer Science+Business Media Dordrecht

Holl K.D.,University of California at Santa Cruz | Zahawi R.A.,Organization for Tropical Studies | Cole R.J.,University of California at Santa Cruz | Ostertag R.,University of Hawaii at Hilo | Cordell S.,U.S. Department of Agriculture
Restoration Ecology | Year: 2011

Planting tree seedlings in small patches (islands) has been proposed as a method to facilitate forest recovery that is less expensive than planting large areas and better simulates the nucleation process of recovery. We planted seedlings of four tree species at 12 formerly agricultural sites in southern Costa Rica in two designs: plantation (entire 50 × 50 m area planted) and island (six patches of three sizes). We monitored seedling survival, height, and canopy area over 3 years. To elucidate mechanisms influencing survival and growth, we measured soil and foliar nutrients, soil compaction, and photosynthesis. Survival of all species was similar in the two planting designs. Seedling height and canopy area were greater in plantations than islands at most sites, and more seedlings in islands decreased in height due to damage incurred during plot maintenance. Survival, height, and canopy area were both site- and species-specific with the two N-fixing species (Inga edulis and Erythrina poeppigiana) greater than the other species (Terminalia amazonia and Vochysia guatemalensis). Foliar N was higher in Terminalia and Vochysia in sites where Inga growth was greater. Soil nutrients, however, explained a small amount of the large differences in growth across sites. Leaf mass per area was higher in islands, and P use efficiency was higher in plantations. Our results show advantages (good seedling survival, cheaper) and disadvantages (more seedling damage, slightly lower growth) to the island planting design. Our study highlights the importance of replicating restoration strategies at several sites to make widespread management recommendations. © 2010 Society for Ecological Restoration International.

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.

Stynoski J.L.,University of Miami | Torres-Mendoza Y.,John Carroll University | Sasa-Marin M.,Organization for Tropical Studies | Sasa-Marin M.,University of Costa Rica | Saporito R.A.,John Carroll University
Ecology | Year: 2014

Many organisms use chemical defenses to reduce predation risk. Aposematic dendrobatid frogs sequester alkaloid-based chemical defenses from a diet of arthropods, but research on these defenses has been limited to adults. Herein, we investigate chemical defense across development in a dendrobatid frog, Oophaga pumilio. This species displays complex parental care: at hatching, mothers transport tadpoles to phytotelmata, and then return to supply them with an obligate diet of nutritive eggs for about six weeks. We collected eggs, tadpoles, juveniles, and adults of O. pumilio, and detected alkaloids in all life stages. The quantity and number of alkaloids increased with frog and tadpole size. We did not detect alkaloids in the earliest stage of tadpoles, but alkaloids were detected as trace quantities in nutritive eggs and as small quantities in ovarian eggs. Tadpoles hand-reared with eggs of an alkaloid-free heterospecific frog did not contain alkaloids. Alkaloids that are sequestered from terrestrial arthropods were detected in both adults and phytotelm-dwelling tadpoles that feed solely on nutritive eggs, suggesting that this frog may be the first animal known to actively provision post-hatch offspring with chemical defenses. Finally, we provide experimental evidence that maternally derived alkaloids deter predation of tadpoles by a predatory arthropod. © 2014 by the Ecological Society of America.

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.

Belisle M.,Stanford University | Mendenhall C.D.,Stanford University | Oviedo Brenes F.,Organization for Tropical Studies | Fukami T.,Stanford University
Fungal Ecology | Year: 2014

Species of yeasts and other microfungi carried by pollinators are of general ecological interest because some of these microbial species can grow in floral nectar and affect plant-pollinator interactions. It is, however, not well understood how the composition of fungal species found on pollinators varies over space or time. The spatial and temporal distribution patterns in the microfungi found on the bills of hummingbirds and in the mouths of nectarivorous bats was investigated along a gradient of deforestation within a Costa Rican countryside landscape. The community composition of microfungi found on hummingbirds' bills and bats' mouths underwent substantial compositional turnover over a 2-month period and between 2yr. In contrast, fungal community composition was not significantly correlated with spatial distance, habitat type, species of hummingbirds, nor the forest dependency of the hummingbirds sampled for microfungi. These findings suggest that, in this landscape, fungal communities on a nectarivous vertebrate vector might be influenced primarily by temporal factors such as plant and flower phenology rather than spatial environmental heterogeneity. © 2014 Elsevier Ltd and The British Mycological Society.

Morrison E.B.,Michigan State University | Lindell C.A.,Michigan State University | Holl K.D.,University of California at Santa Cruz | Zahawi R.A.,Organization for Tropical Studies
Journal of Applied Ecology | Year: 2010

Active restoration to rehabilitate degraded tropical lands often involves planting tree seedlings, an effective but expensive approach if large areas are planted. Planting small patches of vegetation (tens to a few hundred square metres) has recently been suggested as a more economical restoration technique that mimics natural regeneration processes. However, few studies have examined the consequences of restoration patch size on animals, whose presence and activities are often key to successful ecosystem recovery. We examined the effects of patch size on the foraging behaviour of four resident tropical bird species in a replicated forest restoration experiment in southern Costa Rica. We also measured arthropod abundance and anti-predator vigilance behaviour to assess whether variation in food availability or predation risk could explain patch size effects on foraging behaviour. Prey attack rates were highest, and the effort required to find prey was lowest, in larger patches for three of the four bird species. Arthropod density was approximately twice as great in larger patches (>3500 m2) compared with smaller patches (<350 m2). Evidence for patch size differences in predation risk was more limited but risk may be higher in smaller patches. The results indicate that food availability is the primary mechanism driving patch size effects on foraging behaviour, with predation risk being an additional influence for some species in some years. Synthesis and applications. As demonstrated in this study, patches of tens to a few hundreds of metres squared are likely to provide fewer food resources and potentially less cover from predators for vertebrates that use woody habitat, compared with patches of a few thousand square metres. The more limited resources in smaller patches are likely to have short-term and, potentially, long-term consequences for the fitness of organisms. When considering restoration project design, the potential economic and other benefits of planting in smaller patches must be weighed with the potentially negative ecological effects on some taxonomic groups. To increase the probability that patches provide adequate habitat for the largest number of species, we recommend that when financial resources are available, patches of at least a few thousand square metres be planted. © 2009 The Authors. Journal compilation © 2009 British Ecological Society.

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