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Uso del ecotono bosque-sabana por la comunidad de Carnívoros terrestres en los Llanos Orientales de Colombia

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Germán Garrote at IBiCo - Instituto de Biología de la Conservación, Madrid, España
Germán Garrote
  • IBiCo - Instituto de Biología de la Conservación, Madrid, España
Javier Fernández-López at Institute for Game and Wildlife Research
Javier Fernández-López
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Nota breve Galemys, 27 : xx-, 2015
ISSN 1137-8700
e-ISSN 2254-8408
DOI: 10.7325/Galemys.2015.N3
1
El ecotono o transición entre dos tipos de hábitats,
da lugar a un biotopo con propiedades emergentes
únicas que dependen en gran medida de los dos
hábitats que separa y que, debido a su complejidad,
suele jugar un papel importante en la generación
de biodiversidad (Smith et al. 1997). En el caso de
los carnívoros, estos hábitats de transición pueden
resultar importantes, ya sea actuando como corredor
que conecta dos hábitats, propiciando un lugar
adecuado para la captura de presas (Larivière 2003,
May et al. 2010) o para sus desplazamientos diarios
(Svobodová et al. 2011). Por todo ello la conservación
de los ecotonos es relevante para la protección de
ciertas especies de carnívoros (González-Vázquez
2001, Fernández et al. 2003) y de esta forma asegurar
la continuación de los procesos ecológicos en los
que intervienen. Muchas poblaciones de carnívoros
han sufrido una importante disminución de sus
efectivos a nivel mundial como consecuencia de la
persecución humana, la destrucción del hábitat y su
fragmentación (Woodroffe 2000, Dirzo et al. 2014).
Los Llanos Orientales del Orinoco Colombiano
es una región eminentemente ganadera donde las
principales amenazas sobre el hábitat son de origen
antrópico: deforestación y quemas extensivas. Las
quemas afectan en gran medida a la estructura y
composición de la vegetación leñosa en el ecotono
bosque de galería-sabana (Garibello 2001),
pudiendo llegar a hacer desaparecer el gradiente
vegetal natural. En este área se concentra la mayor
concurrencia de fuegos extensivos de los Llanos
Colombianos (Romero-Ruiz 2010) y se ubica
dentro de la subregión Llanos de la Orinoquía,
clasificada con bajo nivel de “conocimiento sobre
los mamíferos medianos y grandes”, y nominada
como “Área prioritaria para la Conservación” (Lasso
et al. 2010). En este trabajo se analizó el uso del
ecotono bosque de galería-sabana por la comunidad
de carnívoros terrestres de la altillanura. Para ello
se evaluó la riqueza y uso de los principales tipos
de cobertura vegetal (bosque de rebalse, ecotono y
sabana) por cada una de las especies de carnívoros
terrestres presentes.
El trabajo de campo se desarrolló en la
Reserva Natural Bojonawi, (Puerto Carreño,
Departamento del Vichada, Colombia), en la
Reserva de la Biosfera El Tuparro (Fig.1). La
temperatura media es de 28°C y la precipitación
media anual de 2.176 mm, con dos periodos
climáticos definidos: estación seca (diciembre-
marzo) y estación lluviosa (abril-noviembre)
(IGAC 1996). Tiene una extensión de 1.200 ha
y aproximadamente el 65% de su superficie está
representada por sabanas, bosques de rebalse y
galería de entre 15 y 600 m de ancho a lo largo
de ríos y caños. Las sabanas constituyen el hábitat
más extenso de la reserva, con árboles y arbustos
dispersos. El bosque de rebalse, asociado al margen
del río Orinoco, permanece inundado durante la
época de lluvias, se caracteriza por no presentar
sotobosque y sus árboles pueden alcanzar los 25
m de altura. El ecotono ocupa una franja entre
la sabana y el bosque, aunque ha desaparecido en
algunos puntos debido al efecto de las quemas, y
en él se observa un gradiente descendente en altura
y densidad de arbolado, apareciendo también
cobertura arbustiva (Tadri 2011). Este estudio es el
primer trabajo de campo realizado sobre carnívoros
terrestres, por lo que no existe información previa
sobre este grupo en dicho territorio.
Uso del ecotono bosque-sabana por la comunidad de Carnívoros
terrestres en los Llanos Orientales de Colombia
Germán Garrote1* & Javier Fernández-López2,3
1. Fundación Omacha. C/ 84 Nº 21 - 64, Barrio El Polo, Bogotá D.C, Colombia
2. Real Jardín Botánico de Madrid-CSIC, Plaza de Murillo, 2, 28014 Madrid, España
3. Departamento de Zoología y Antropología Física, Facultad de Ciencias Biológicas, Universidad Complutense,
28040 Madrid, España
*Autor para correspondencia: gergarrote@gmail.com
Galemys 27, 2015
2
Durante los meses de enero a marzo de 2006 y
2007 se realizaron muestreos periódicos en busca
de indicios de carnívoros. Se realizaron transectos a
pie por caminos, veredas, caños y otros elementos
lineales del territorio, utilizados habitualmente
por los carnívoros en sus desplazamientos y
marcaje (Barea-Azcón et al. 2007). Se consideraron
únicamente las huellas como indicio de presencia de
la especie. Cuando se detecto un rastro compuesto
por una secuencia de huellas se consideró un único
registro. Se diseñó un itinerario de 2 km en cada
uno de los hábitats considerados (bosque galería,
ecotono y sabana) y se recorrió en tres ocasiones.
Además, se realizaron itinerarios no fijos en busca
de indicios en cada uno de los hábitats, hasta
completar un esfuerzo total de muestreo de 20 km
(6 km fijos + 14 km al azar) en cada hábitat, para
cubrir la mayor superficie posible de cada uno de
ellos. Se empleó la prueba de Chi cuadrado (c2)
con el fin de comprobar la desviación entre el
número de indicios observados y los esperados en
cada hábitat.
Se detectaron un total de 47 indicios (huellas/
rastros) de presencia de cuatro especies de carnívoros:
tres felinos (yaguar, Panthera onca; ocelote, Leopardus
pardalis y yaguarundi, Puma yagouaroundi) y un
cánido (Zorro cangrejero, Cerdocyon thous). Las
cuatro especies fueron detectadas tanto en el bosque
como en el ecotono, mientras que en la sabana sólo
se detectó al zorro cangrejero (Fig. 2). El hábitat
más utilizado por la comunidad de carnívoros fue el
ecotono (47,9% de los indicios detectados), seguido
del bosque (31,3%) y por último la sabana (20,8%).
Los carnívoros usaron significativamente más el
ecotono que la sabana (c2= 5,12, df=1, p= 0,023),
mientras que usaron por igual ecotono y bosque
(c2= 1,68, df= 1, p= 0,194). Los felinos presentes en
el área de estudio usaron en igual medida el ecotono
y el bosque (c2= 0,13, df=1, p= 0,715), mientras
que no fueron detectados en la sabana. El escaso
Figura 1. Localización de la Reserva Natural Bojonawi, y representación de los principales
hábitats del área de estudio.
Figura 2. Número de indicios
(huellas/rastros) encontrados en cada
tipo de hábitat para cada una de las
especies consideradas, para el total
de los carnívoros y para el total de
felinos.
G. Garrote & J. Fernández-López
3
número de indicios detectados para cada especie no
permitió la aplicación de análisis estadísticos, a pesar
de lo cual se encontraron marcados patrones de uso
de los diferentes hábitats. Se detectaron un mayor
número de indicios de P. onca y P. yagouaroundi en
ecotono que en bosque, mientras que se detectaron
más indicios de L. pardalis en bosque que en
ecotono. El único cánido presente, C. thous, prefirió
espacios abiertos como la sabana para desarrollar
su actividad, encontrándose con frecuencia en el
ecotono y ocasionalmente en el bosque.
A pesar de ser un hábitat escaso en este tipo de
ecosistemas, el ecotono presenta un elevado uso
por parte de la comunidad de carnívoros terrestres.
Estudios previos han encontrado similares patrones
de distribución de carnívoros en hábitats de borde
(Dijack & Thompson 2000, Svobodová et al.
2011). Esta información apunta a que el ecotono
podría jugar un papel importante en la ecología de
estas especies en los ecosistemas de sabana donde
los hábitats forestales son escasos. Nuestro diseño de
estudio no permite conocer las causas subyacentes
a la distribución de los carnívoros encontrada.
Futuras investigaciones deben profundizar en el
estudio de los mecanismos implicados en el uso de
ecotono por parte de los carnívoros que permitan
ponderar adecuadamente su importancia y evaluar
el efecto que su reducción o su pérdida puede causar
sobre cada especie.
Desde el punto de vista ecológico, el fuego es un
proceso implícito en la configuración y estructura
de las sabanas, y aunque estos eventos han tenido
históricamente causas naturales, actualmente los
incendios provocados en los Llanos Orientales
llegan a ser en torno al 80% (Romero-Ruiz 2010).
Las quemas recurrentes pueden constituir una
amenaza, tanto como la tala, si se toma en cuenta
que ciertas áreas de sabana podrían estar ocupadas
por bosque si no se diesen dichas perturbaciones
(Rial 2006). La reducción o pérdida del ecotono
en estos ecosistemas de sabana, donde el hábitat
forestal es tan escaso, implica un importante
descenso de la superficie de hábitat útil para los
carnívoros, siendo la comunidad de felinos la más
afectada al preferir notablemente los ambientes
forestales frente a los de menor cobertura
(Scognamillo et al. 2003, Zarza et al. 2007). En
el caso de la reserva Bojonawi, el ecotono ocupa
tan solo el 15% de la superficie forestal debido
al efecto histórico de las quemas. Esta superficie
podría ampliarse notablemente si se redujera el
impacto de las mismas. Mediante la aplicación
de simples medidas preventivas, como el uso de
fajas cortafuegos que limitaran el acceso de las
quemas a las zonas de ecotono, se podría alcanzar
un equilibrio entre la conservación de estas áreas
prioritarias para la conservación y el mantenimiento
de pastos para la actividad ganadera.
Agradecimientos
Este estudio fue realizado en el marco del proyecto
“Pi jiwi Orinoko” Fundación Omacha - Fundación
Horizonte Verde y Forest Conservation Agreement.
Agradecemos a la Fundación Omacha su apoyo durante
el desarrollo de este trabajo, especialmente a F. Trujillo,
M.C. Diazgranados, J.Terán “Don Jacinto”, “Lucho”
Trujillo, C. Gómez e I. Gómez. David Camps y un
revisor anónimo realizaron importantes aportes que
mejoraron la calidad el manuscrito.
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Associate editor was Jordi Ruiz-Olmo
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... Specifically, for the Colombian Llanos (Orinoco Region), information is almost completely absent, with not even basic approaches to its distribution, conflict or any other ecological or conservation-related aspects (González-Maya et al. 2019b). Yet, the Llanos region is one of the most important regions for conservation in the country (Garrote and Fernández-López 2015;Lasso et al. 2010), comprising nearly 30% of the total country terrestrial territory and maintains an important percentage of the country's natural coverage due to partial isolation from the densely populated areas (Etter et al. 2006a(Etter et al. , 2006bGarrote and Fernández-López 2015), and together with the Venezuelan llanos, constitutes the main tropical savannas in northern South America (Armenteras et al. 2005;Berrio et al. 2000). Furthermore, the region is considered one of the last frontiers for the conservation of Neotropical savannas, still retaining good conservation status and opportunities given its isolation and human history (Lasso et al. 2011;Romero-Ruiz et al. 2012); moreover, it is one of the most unique but least understood ecosystems in the country, especially in terms of its biodiversity and specifically its mammals' fauna (Correa-Gómez and Stevenson 2010;Pardo et al. 2018Pardo et al. , 2019Lasso et al. 2010). ...
... Our results indicate how pumas might selectively avoid proximity to towns, and as such human settlements encroach in these landscapes, we could expect larger effects over available habitats in the Llanos region. In terms of distance to rivers, in our study area rivers in general are largely associated with forests given the ecological conditions of the typical Llanos ecosystem (Armenteras et al. 2005;Correa-Gómez and Stevenson 2010;Garrote and Fernández-López 2015). This proximity to riparian corridors is likely related with refuge, prey availability and habitat quality in general, although studies in similar regions have indicated females might select open dry pastures more than expected, males do not show the same behavior (Farrell and Sunquist 1999;Scognamillo et al. 2003) however, also these and other studies have indicated that pumas tend to expend most of their time in closeness, proximity to large forest patches (Farrell and Sunquist 1999;Scognamillo et al. 2003) which in our study area are mostly related with riparian corridors, and tend to use more frequently river beds and riparian corridors during the dry season and for dispersal (Morrison et al. 2015;Nuñez-Perez and Miller 2019) because of water availability and plant cover (Beier 1995;Nuñez-Perez and Miller 2019). ...
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... Se instalaron 9 estaciones de fototrampeo en caminos y veredas, separadas entre sí una distancia de 1.071 ± 419 m, cubriendo de manera más homogénea posible las áreas forestales (bosque de rebalse y ecotono) de la reserva. Las cámaras fueron instaladas solo en áreas forestales para maximizar la probabilidad de captura de los ocelotes (Karanth & Nichols 1998), ya que estudios previos en la reserva demostraron que éstas son las áreas usadas preferentemente por la especie (Garrote & Fernández 2015). Cada estación de fototrampeo estaba compuesta por una única cámara, a excepción de una de ellas, en la cual se instalaron dos cámaras enfrentadas para obtener fotografías simultaneas de ambos flancos del animal. ...
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... Este paisaje está compuesto por bosques de galería y sabanas abiertas; no hay grandes extensiones de bosque continuo con cobertura densa (Romero et al. 2004) y esto implica una menor densidad y diversidad de pequeños mamíferos presa (Abreu et al. 2008). A su vez, esto implica una baja disponibilidad de hábitats forestales, que son los -preferidos‖ por los ocelotes (Garrote & Fernández-López 2015). En el caso particular del bosque del rebalse del Orinoco, el hecho de no tener sotobosque y permanecer inundado (al igual que las áreas de ecotono) durante toda la estación lluviosa, posiblemente este limitando la presencia de mamíferos terrestres forestales de mediano y pequeño tamaño. ...
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  • Apr 2007
  • BIODIVERS CONSERV
Reliable methods to estimate species richness are very important to managers and conservationists because they provide key data to make the right decisions in conservation programmes. In the case of carnivore mammals, traditional methods, such as direct count censuses, are not useful since these animals are usually scarce, elusive and nocturnal. Difficulties in carnivore sampling are compounded when monitoring programmes are developed at large spatial scales, where high economic costs and field efforts are necessary to achieve reliable richness or abundance estimates. These problems have highlighted the need to find more effective carnivore survey methods, especially in regions with high rates of landscape change, such as the Mediterranean basin. The present study, performed in a typical Mediterranean area, was the first in Europe to test simultaneously the relative efficiencies of four broad-applied sampling methods to detect carnivore species at large spatial scales. Sign surveys based on scat detection, scent stations, camera-trapping and live-trapping were investigated. We compared efficiencies using biological parameters and by considering both the logistic and economic costs of each method. Overall, scent stations and sign surveys were the most efficient methods both in economic and logistic terms. In addition, the use of scent stations may be necessary to detect species rarely detected by scats. Detailed and extensive training programmes for conducting sign surveys and scent stations may overcome perceived problems thus enhancing the widespread use of both methods. Our results are applicable not only to other Mediterranean areas, but also to other habitats and regions of the world. More research into the suitability of these and other methods in relation to different landscapes, seasons and species is required.
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Identifying breeding habitat for the Iberian lynx: Inferences from a fine-scale spatial analysis
Article
Full-text available
  • Jan 1310
Empirical landscape habitat models are valuable tools for addressing species conservation issues in heterogeneous landscapes. These have been particularly useful for animal populations requiring extensive areas, like large mammalian carnivores. Although models are scale-dependent, they are often based exclusively on coarse-grained information on landscape structure and species distribution. However, accurate discrimination and qual-ity assessment of breeding habitats may require more detailed information on both indi-viduals' habitat use and landscape patterns. Here, we modeled breeding habitat for the Iberian lynx (Lynx pardinus), an endangered specialist of Mediterranean native ecosystems, in a human-dominated landscape. For this, we used radiotelemetry data on breeding individuals and fine-grained landscape variables obtained over an areal extent encompassing an entire lynx metapopulation. In addition, we restricted the study domain to areas of potential presence within this extent based on previous habitat analyses. This fine-scale landscape analysis and design aimed to test wheth-er it was possible to obtain detailed inferences on breeding habitat distribution and quality within more coarsely defined habitats that only indicate where the species can be found. Landscape composition factors (i.e., fine-grain variables of landscape pattern within ter-ritories) and context factors (variables on geographical location of territories) were com-bined in different candidate habitat models. These reflected various hypotheses involving territory presence and size, including vegetation structure characteristics, landscape het-erogeneity and complexity, favorable prey habitat, and human disturbance. The best ap-proximating model for territory presence included only one landscape composition variable, namely, density of ecotones between scrubland and pastureland, which favored presence. For this model, classification accuracy was 80% in 94% of cross-validation tests per-formed. The best approximating model for territory size explained 65% of the variation in size and included also density of ecotones, plus mean coverage of tall shrubs within ter-ritories; both correlated negatively with size. We show how these predictors are also related to prey density and suggest that this low-hierarchical-level relationship between the prey and patterns of the landscape can be interpreted as a likely mechanism explaining breeding habitat distribution and quality at a higher level. Our approach shows the potential of fine-scale landscape analysis to understand patterns of breeder abundance, and to better manage population viability of threatened species in human-populated areas.
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Edge Effects, Predator Movements, and the Travel-Lane Paradox
Article
  • Mar 2003
High predation rates on bird nests located near habitat edges are often explained by the presumed use of edges as "travel lanes" by mammalian predators. Through repetitious and indiscriminate citing, the travel-lane concept has become dogma. I review the empirical evidence of use of habitat edges by mammals that are commonly identified as predators of bird eggs. I argue that 1) earlier works did not provide evidence that predators used edges as travel lanes, 2) strong empirical evidence that mammalian predators use edges as travel lanes is lacking, and 3) increased use of edges by predators, if it occurs, may result from several alternate processes such as greater foraging efficiency near edges or simply greater predator density or diversity. Furthermore, I caution that use of narrow and linear habitats such as fencelines and roadways by foraging or travelling predators does not constitute "edge use" because these habitats are too narrow to include habitat interior. Until further work confirms or refutes the use of edges by predators, caution is warranted before referring to edges acting as travel lanes for mammalian predators.
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Landscape and Edge Effects on the Distribution of Mammalian Predators in Missouri
Article
  • Jan 2000
Raccoons (Procyon lotor), opossums (Didelphis virginiana), and striped skunks (Mephitis mephitis) are predators of forest songbird eggs and nestlings. We examined the relative abundance of these predators at landscape and local scales to better understand predation risks. At the landscape scale, we examined the relationship between detection rates of raccoons, opossums, and striped skunks on 25 scent-station routes distributed across Missouri and surrounding landscape characteristics. Raccoon abundance was related to latitude, stream density, and mean patch size of agricultural lands. Opossum abundance was related to stream density, contagion, mean nearest-neighbor distance between forest patches, and latitude. Striped skunk abundance was not related to landscape characteristics we examined. At a local scale, we used sooted-plate scent stations to compare the relative abundance of raccoons and opossums in forest interiors to forests adjacent to agricultural fields, roads, clearcuts, and streams. Raccoons were more-abundant in forest edges adjacent to agricultural fields and streams. Opossum abundance varied greatly among years and there was no consistent edge effect on abundance. Local features such as proximity to some types of edge as well as large-scale factors such as landscape patterns in land. use may affect predator abundance and potentially songbird-nest predation rates.
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Coexistence of jaguar (Panthera onca) and puma (Puma concolor) in a mosaic landscape in the Venezuelan IIanos
Article
Jaguar Panthera onca and puma Puma concolor are sympatric throughout the jaguar's distribution. Although several studies have focused on the interactions between these two predators, the ecological and behavioural factors that promote their coexistence remain unclear. The goal of this study was to identify those factors that facilitate the coexistence of these cats in a mosaic landscape in the Venezuelan llanos. The study was conducted from January 1996 until November 1998. Five jaguars and six pumas were captured and radio-collared. A high degree of spatial overlap was observed between jaguars and pumas, which may be related to the abundance and distribution of prey species. At a fine scale, there was little overlap of puma locations with jaguar locations. Both species were more active at night than during daytime, but seasonal differences were detected in the activity levels of these predators. Major segregation was found in food habits. Jaguars selected for large prey and pumas for medium-sized prey. Jaguars selected for capybara Hydrochaeris hydrochaeris and collared peccary Tayassu tajacu and consumed caiman Caiman crocodilus and white-tailed deer Odocoileus virginianus less than expected. Pumas selected just for collared peccary and also killed caiman less than expected. It is suggested that the abundance of medium-sized prey is an ecological factor that is facilitating the coexistence of jaguar and puma in the study area. Habitat heterogeneity may be another influential factor leading to the coexistence. Seasonal differences in activity levels probably reflect differences in the size and species of prey taken by these cats.
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Predators and people: Using human densities to interpret declines of large carnivores
Article
The current extinction crisis is caused primarily by human impacts upon wild populations. Large carnivores are especially sensitive to human activity; because their requirements often conflict with those of local people, predators have been actively persecuted in most regions of the world. In this paper, the impact of people upon predators is analysed by relating local carnivore extinctions to past and projected human population densities. There are strong associations between high human density and the loss of carnivore populations from a region. Interspecific variation in ability to survive at high human densities probably reflects species' ability to adapt to human-modified habitats. However, regional and temporal variation in individual species' sensitivity to human density is more likely to reflect the activities of local people than the phenotypes of local carnivores. Local culture, government policy and international trade all influence human attitudes to predators and, therefore, the impact of people upon carnivore populations. The importance of these factors may mean that extinction risks for carnivores will continue to increase, even though human population growth is projected to deccelerate during the new millennium. This points to an urgent need for techniques to resolve conflicts between people and predators at either the local or landscape level.
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Surveying carnivores at large spatial scales: a comparison of four broad-applied methods
Chapter
  • Sep 2007
Reliable methods to estimate species richness are very important to managers and conservationists because they provide key data to make the right decisions in conservation programmes. In the case of carnivore mammals, traditional methods, such as direct count censuses, are not useful since these animals are usually scarce, elusive and nocturnal. Difficulties in carnivore sampling are compounded when monitoring programmes are developed at large spatial scales, where high economic costs and field efforts are necessary to achieve reliable richness or abundance estimates. These problems have highlighted the need to find more effective carnivore survey methods, especially in regions with high rates of landscape change, such as the Mediterranean basin. The present study, performed in a typical Mediterranean area, was the first in Europe to test simultaneously the relative efficiencies of four broad-applied sampling methods to detect carnivore species at large spatial scales. Sign surveys based on scat detection, scent stations, camera-trapping and live-trapping were investigated. We compared efficiencies using biological parameters and by considering both the logistic and economic costs of each method. Overall, scent stations and sign surveys were the most efficient methods both in economic and logistic terms. In addition, the use of scent stations may be necessary to detect species rarely detected by scats. Detailed and extensive training programmes for conducting sign surveys and scent stations may overcome perceived problems thus enhancing the widespread use of both methods. Our results are applicable not only to other Mediterranean areas, but also to other habitats and regions of the world. More research into the suitability of these and other methods in relation to different landscapes, seasons and species is required.
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