LIVE FENCES HAVE GREATER DIVERSITY OF BIRD ASSEMBLAGES THAN GALLERY FORESTS IN HUMAN-MODIFIED ECOSYSTEMS

Anthropogenic activities have led to changes in land use resulting in fragmented areas with a reduction of biodiversity and ecosystem services. Gallery forests and live fences are common elements in Neotropical agricultural landscapes that could contribute to the conservation of bird species and the services they provide. However, we need to better understand how different tree cover types influence bird assemblages in order to conserve biodiversity. I analysed the diversity of bird assemblages in space and time across two cover types in three agricultural-livestock farms in Guanacaste, Costa Rica. Bird assemblages were sampled during 2019 using transects, covering both the dry and rainy season. I estimated richness and relative abundance of bird assemblages at each tree cover type and site. To characterize vegetation structure, I calculated plant richness, diameter at breast height and tree height. Patterns in bird diversity changed at a spatial scale, whereas remained similar in time. Bird assemblages had consistently higher richness and abundance in live fence than in gallery forest in the three study sites. In addition, live fences resulted in a less structural complexity compared to gallery forest, as indicated by decreased plant richness and tree height. My results show that live fences play an important role for birds, allowing for more diverse avian assemblages in human-modified ecosystems. Although live fences are less structurally complex and may offer less suitable habitats for birds than gallery forests, they might provide complementary food resources and act as stepping-stones for both resident and migratory bird species. Thus, live fences may perform as corridors for birds increasing connectivity in rural landscapes, which make them an essential tool for bird conservation

Desarrollo de las piñeras en Costa Rica y sus impactos sobre ecosistemas naturales y agro-urbanos

Development of pineapple crops in Costa Rica and their impacts of natural and agro-urban ecosystems. In the early eighties pineapple production achieved international projection, at which time a new development model based on non-traditional exports in Costa Rica gathered strength due to new demands of the international market. From this, they entrenched a system of incentives and political and institutional framework to support the export of new products. By then the pineapple monoculture acquired an expansive character, covering large areas of land and employing high levels of agrochemicals. This caused a number of impacts on socio-economic, natural ecosystems and agro-urban systems. In Costa Rica, there have been impacts especially in the North, South and Caribbean zones and more recently has begun to spread also in the North Pacific. Some organizations have begun to venture into organic pineapple cultivation, characterized by a lesser extent in land use and the use of chemicals to a lesser extent and more controlled. This type of pineapple cultivation along with a series of measures to promote proper waste management of the fruit may help to reduce the negative effects on pineapple crops. However, because organic cultivation will not eradicate environmental problems, it would be practical to adjust production towards a diversification of activities, avoiding the typical impacts caused by any monoculture. A principios de los años ochenta, la producción de piña logró proyectarse internacionalmente, momento en el que un nuevo modelo de desarrollo basado en las exportaciones no tradicionales tomó impulso en Costa Rica, debido a las nuevas demandas del mercado internacional. A partir de esto, se afianzó un sistema de incentivos y un marco político e institucional de apoyo a la exportación de nuevos productos. Para ese entonces, el monocultivo de la piña adquirió un carácter expansivo, abarcando grandes extensiones de tierra y empleando altos niveles de agroquímicos. Esto desencadenó una serie de impactos tanto a nivel socio-económico como sobre los ecosistemas naturales y agro-urbanos. En Costa Rica, se han presentado impactos especialmente en las zonas Norte, Sur y Caribe y más recientemente el cultivo ha empezado a extenderse también en el Pacífico Norte. Algunas organizaciones han comenzado a incursionar en el cultivo de piña orgánica, caracterizada por una menor extensión en el uso del suelo y el uso de agroquímicos en menor medida y de manera más controlada. Esta modalidad del cultivo piña junto con una serie de medidas que favorezcan un adecuado manejo de los desechos de la fruta podrían contribuir a reducir los efectos negativos. No obstante, debido a que con los cultivos orgánicos no se ven erradicados los problemas ambientales, resulta conveniente orientar la producción hacia una diversificación de actividades, evitando los impactos típicos ocasionados por cualquier monocultivo. 

El uso de especies vegetales exóticas como una estrategia de restauración ecológica

El presente artículo describe el desarrollo de programas de reforestación en Costa Rica y el uso de especies vegetales exóticas para la recuperación de tierras degradadas en los trópicos. Se lleva a cabo un análisis de las ventajas y desventajas del uso de estas especies en programas de restauración ecológica

Restauración ecológica: perspectiva histórica e implicaciones éticas de una disciplina en crecimiento

Actualmente la restauración ecológica es uno de los campos de mayor crecimiento en ecología aplicada, ofrece nuevas ideas y oportunidades para la conservación de la biodiversidad y el manejo de los recursos naturales. La ecología de la restauración (la teoría) y la restauración ecológica (la práctica) buscan la recuperación de la estructura y función de un ecosistema acelerando los procesos ecológicos que tienen lugar. En el pasado, la restauración ecológica ha sido criticada, entre otras cosas por no considerar un énfasis adecuado sobre el desarrollo de una metodología estructurada típica de cualquier disciplina científica. A su vez, existen una serie de objeciones de tipo éticas y filosóficas en torno a esta disciplina, se plantea la duda de si es posible o no, realizar la recuperación de los ecosistemas que pretende llevarlos al estado prístino en que se encontraban previo a su deterioro o pérdida. El desarrollo humano consecuencia de un incremento poblacional acelerado, implica que el deterioro ambiental resulte posiblemente inevitable, aún cuando se intenta enmarcarlo dentro de un contexto de sostenibilidad. La restauración ecológica aunque difícil de alcanzar, debido a las características únicas e irrepetibles de los ecosistemas, representa hoy en día una alternativa para preservar la diversidad biológica y constituye el principal complemento de la biología de la conservación

Factores que afectan la Reserva Forestal Grecia (Alajuela, Costa Rica) disminuyendo su valor para la conservación de la biodiversidad

El presente artículo se elaboró como resultado del proyecto “Determinación del estado de conservación de la Reserva Forestal Grecia por medio de la comunidad vegetal y especies de aves para el análisis de estrategias de restauración ecológica”. Describe los principales factores que afectan actualmente a esta Reserva y que por lo tanto reducen su valor en la conservación de la biodiversidad. La información se obtuvo a partir de observaciones en el sitio, entrevistas a funcionarios de la Reserva y literatura científica, entre setiembre de 2008 y noviembre de 2009. Entre los principales factores que afectan a la Reserva se encuentran: avance de la frontera urbana, contaminación por actividades agropecuarias, introducción de especies forestales exóticas, captura y trasiego de vida silvestre, altos niveles de ruido, incendios forestales y captación de fuentes de agua

Efecto del cambio climático sobre las interacciones planta-animal y sus consecuencias sobre los ecosistemas

Las comunidades ecológicas están organizadas en redes complejas de interacción donde las especies se relacionan unas con otras a través de diferentes tipos de interacciones. Las interacciones mutuamente benéficas entre plantas y sus polinizadores y dispersores de semillas tienen una gran influencia en la dinámica de la comunidad y han contribuido a generar la biodiversidad sobre la Tierra. Además, las interacciones mutualistas planta-animal son claves en proveer funciones y servicios ecosistémicos. El cambio climático es una amenaza significativa para las especies y sus interacciones en las comunidades ecológicas, con el potencial de modificar funciones y servicios ecosistémicos claves como la polinización y la dispersión de semillas. Las interacciones mutualistas son especialmente vulnerables a ser afectadas por el cambio climático debido a su alta sensibilidad al desacople fenológico si las especies que interactúan no responden de manera similar a los cambios ambientales. En interacciones planta-polinizador y planta-dispersor de semilla, el desacople fenológico puede afectar a las plantas causando una reproducción reducida, mientras que los polinizadores y dispersores de semilla se ven afectados por una menor disponibilidad de alimento. La declinación de polinizadores y dispersores de semilla puede conducir a la pérdida de interacciones en las comunidades, lo cual puede a su vez onducir al colapso de las funciones y servicios ecosistémicos que mantienen. Estas consecuencias podrían ser particularmente severas en los trópicos, donde existe una alta dependencia de la polinización y dispersión de semilla por medio de animales

When cheating turns into a stabilizing mechanism of plant-pollinator communities.

Mutualistic interactions, such as plant-mycorrhizal or plant-pollinator interactions, are widespread in ecological communities and frequently exploited by cheaters, species that profit from interactions without providing benefits in return. Cheating usually negatively affects the fitness of the individuals that are cheated on, but the effects of cheating at the community level remains poorly understood. Here, we describe 2 different kinds of cheating in mutualistic networks and use a generalized Lotka-Volterra model to show that they have very different consequences for the persistence of the community. Conservative cheating, where a species cheats on its mutualistic partners to escape the cost of mutualistic interactions, negatively affects community persistence. In contrast, innovative cheating occurs with species with whom legitimate interactions are not possible, because of a physiological or morphological barrier. Innovative cheating can enhance community persistence under some conditions: when cheaters have few mutualistic partners, cheat at low or intermediate frequency and the cost associated with mutualism is not too high. Under these conditions, the negative effects of cheating on partner persistence are overcompensated at the community level by the positive feedback loops that arise in diverse mutualistic communities. Using an empirical dataset of plant-bird interactions (hummingbirds and flowerpiercers), we found that observed cheating patterns are highly consistent with theoretical cheating patterns found to increase community persistence. This result suggests that the cheating patterns observed in nature could contribute to promote species coexistence in mutualistic communities, instead of necessarily destabilizing them

Macroevolution of the plant–hummingbird pollination system

ABSTRACTPlant–hummingbird interactions are considered a classic example of coevolution, a process in which mutually dependent species influence each other's evolution. Plants depend on hummingbirds for pollination, whereas hummingbirds rely on nectar for food. As a step towards understanding coevolution, this review focuses on the macroevolutionary consequences of plant–hummingbird interactions, a relatively underexplored area in the current literature. We synthesize prior studies, illustrating the origins and dynamics of hummingbird pollination across different angiosperm clades previously pollinated by insects (mostly bees), bats, and passerine birds. In some cases, the crown age of hummingbirds pre‐dates the plants they pollinate. In other cases, plant groups transitioned to hummingbird pollination early in the establishment of this bird group in the Americas, with the build‐up of both diversities coinciding temporally, and hence suggesting co‐diversification. Determining what triggers shifts to and away from hummingbird pollination remains a major open challenge. The impact of hummingbirds on plant diversification is complex, with many tropical plant lineages experiencing increased diversification after acquiring flowers that attract hummingbirds, and others experiencing no change or even a decrease in diversification rates. This mixed evidence suggests that other extrinsic or intrinsic factors, such as local climate and isolation, are important covariables driving the diversification of plants adapted to hummingbird pollination. To guide future studies, we discuss the mechanisms and contexts under which hummingbirds, as a clade and as individual species (e.g. traits, foraging behaviour, degree of specialization), could influence plant evolution. We conclude by commenting on how macroevolutionary signals of the mutualism could relate to coevolution, highlighting the unbalanced focus on the plant side of the interaction, and advocating for the use of species‐level interaction data in macroevolutionary studies

The macroecology of phylogenetically structured hummingbird-plant networks

Aim To investigate the association between species richness, species' phylogenetic signal, insularity and historical and current climate with hummingbird-plant network structure. Location 54 communities along a c. 10,000 kilometer latitudinal gradient across the Americas (39ºN - 32ºS), ranging from sea level to c. 3700 m asl, located on the mainland and on islands, and covering a wide range of climate regimes. Methods We measured null-modeled corrected complementary specialization and bipartite modularity (compartmentalization) in networks of quantitative interactions between hummingbird and plant species. Using an ordinary least squares multi-model approach, we examined the influence of species richness, phylogenetic signal, insularity, and current and historical climate conditions on network structure. Results Phylogenetically-related species, especially plants, showed a tendency to interact with a similar array of partners. The spatial variation in network structure exhibited a constant association with species' phylogeny (R2=0.18-0.19). Species richness and environmental factors showed the strongest associations with network structure (R2=0.20-0.44; R2138 =0.32-0.45, respectively). Specifically, higher levels of complementary specialization and modularity were associated to species-rich communities and communities in which closely-related hummingbirds visited distinct sets of flowering species. On the mainland, warmer temperatures and higher historical temperature stability associated to higher levels of complementary specialization. Main conclusions Previous macroecological studies of interaction networks have highlighted the importance of environment and species richness in determining network structure. Here, for the first time, we report an association between species phylogenetic signal and network structure at macroecological scale. Specifically, null model corrected complementary specialization and modularity exhibited a positive association with species richness and a negative association with hummingbird phylogenetic signal, indicating that both high richness and high inter-specific competition among closely-related 150 hummingbirds exhibit important relationships with specialization in hummingbird-plant networks. Our results document how species richness, phylogenetic signal and climate associate with network structure in complex ways at macroecological scale