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Sample size and appropriate design of fruit and seed traps in tropical forests

Published online by Cambridge University Press:  01 January 2008

Pablo R. Stevenson  and
Ivonne N. Vargas
Pablo R. Stevenson*
Affiliation:
CIEM, Departamento de Ciencias Biológicas, Universidad de los Andes. Cr. 1a No. 18A-10. Bogotá, Colombia
Ivonne N. Vargas
Affiliation:
CIEM, Departamento de Ciencias Biológicas, Universidad de los Andes. Cr. 1a No. 18A-10. Bogotá, Colombia
*
1Corresponding author. Email: pstevens@uniandes.edu.co
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Abstract:

Studies of seed dispersal and fruit production often use fruit traps. Different trap designs may give dissimilar estimates; however, prior to this study there has been no tropical forest field comparison of trap designs. Likewise, there are no recommendations about the number of traps required to assess ecological parameters, such as fruit production, mass and number of seeds dispersed, and number of plant species producing fruits. We compared the effectiveness of five trap designs in terms of fruit/seed bouncing out of traps, wind effects, area effects and seed removal by predators. These studies took place in Colombia in two tropical rain forests and in laboratory conditions. We found that 300 traps (0.085 m2 each) were not enough to obtain stable estimates in two out of four parameters (number of species and dispersed seeds). All estimates were highly variable when using fewer than 100 traps. All trap designs evaluated (mesh on PVC frame, hanging mesh, basin and funnel traps) prevent seed removal by predators, in sharp contrast with removal from the ground. Mesh traps were less affected by bouncing effects than plastic traps, and this factor was a large source of bias among estimates from different traps. Since up to 68% of dry mass may bounce out, it is important to consider adequate trap designs and to be careful when comparing studies using different methodologies. Small traps received fewer seeds per area, however area affects were not evident when bouncing effects were controlled for. We recommend the use of mesh traps on PVC frames, although hanging mesh traps are a good option in tropical forests without strong winds.

Resumen:

Los estudios de dispersión de semillas y producción de frutos frecuentemente utilizan trampas. Diferentes diseños de trampa pueden aportar estimativos distintos, pero esto no ha sido evaluado en bosques tropicales y tampoco hay recomendaciones sobre el número de trampas requerido para cuantificar producción de frutos, biomasa y número de semillas dispersadas, y número de especies de plantas representadas. Comparamos la efectividad de 5 diseños, en términos de efectos de rebote, área de recolección y remoción por viento y por animales. Estos estudios se hicieron en Colombia en dos bosques húmedos tropicales y en condiciones de laboratorio. Trescientas trampas de 0.085 m2 no fueron suficientes para conseguir estimativos estables en dos de los cuatro parámetros evaluados (número de especies y de semillas dispersadas). Encontramos que todos los estimativos son muy variables cuando se usan menos de 100 trampas. Todos los diseños de trampa (malla con estructura de PVC, malla colgante, platón y embudo) evitan de manera similar la remoción por parte de animales, en contraste con la alta remoción en el suelo. Las trampas de malla fueron menos afectadas por efectos de rebote que las trampas de plástico, y estas diferencias alteran substancialmente los estimativos de producción. Ya que hasta un 68% de la masa seca puede rebotar, es importante considerar cuales son los mejores diseños de trampa y ser cuidadoso en el momento de comparar estudios que usan diferentes métodos. Encontramos menos semillas por unidad de área en trampas pequeñas, pero el efecto de área de recolección no fue significativo al tener en cuenta los efectos de rebote. Recomendamos el uso de trampas de malla con estructura de PVC para estudios en bosques tropicales, aunque las trampas de malla colgante son una buena opción en lugares sin vientos fuertes.

Keywords

Biased estimatesCaparúfruit productionfruit trapsmethodologyseed dispersaltrap designTinigua National Park
Type
Research Article
Information
Journal of Tropical Ecology , Volume 24 , Issue 1 , January 2008 , pp. 95 - 105
Copyright
Copyright © Cambridge University Press 2008

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