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Ben Gurion University of the Negev (2012)

Spillover of agriculturally subsidized arthropods to adjacent natural arid habitats : effects on community structure

Hochman-Adler Valeria

Titre : Spillover of agriculturally subsidized arthropods to adjacent natural arid habitats : effects on community structure

Auteur : Hochman-Adler Valeria

Université de soutenance : Ben Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2012

Spillover of arthropods from agricultural areas may affect the dynamics of food webs in adjacent natural habitats. I studied the occurrence of pest spillover from agricultural fields into surrounding non-crop habitat, its timing with respect to the cropping season, the degree of spillover at increasing distance from the crop, and its effects on the desert arthropod community in the hyper-arid Arava Valley, Israel. My working hypotheses were that pests will move from ephemeral high productivity habitats into low productivity habitats, and that spillover of pests will alter the structure of the recipient desert arthropod community. The Arava Valley provides a unique opportunity for studying pest spillover effects, as the arable land is surrounded by desert habitat, forming productive “islands” in a desert matrix. Particularly, I was interested in four main questions : 1) Is there pest spillover from crops into adjacent desert habitat, and does it decrease along a gradient of increasing distance from agricultural fields ? 2) If spillover occurs, can pests survive and reproduce in desert habitats ? This is relevant as pests may subsidize desert predators, scavengers, or both. 3) Are pests consumed by desert predators, and do they influence predator intraguild interactions ? and 4) Are there changes in species composition in the desert arthropod community as a consequence of pest spillover ? I investigated these questions by studying the abundance and dispersal of crop pests from agricultural areas into adjacent desert habitats, and their interactions with natural-habitat species. First, I monitored pest occurrence over the crop cycle in desert habitats and in home gardens in villages near agricultural areas. Second, I tested pest persistence and reproduction on desert plants. Third, I conducted lab experiments to investigate interactions between pests and desert predators, and to test some of the pathways by which spillover of pests might influence the desert arthropod community. Finally, I sampled the desert arthropod communities along a gradient of increasing distance from agricultural fields. This study attempted to improve our understanding of the effects of agricultural pests on natural ecosystem biodiversity in an extreme desert environment. I showed that pests spill over into adjacent natural habitats, and survive on some desert plant species within these habitats. In addition, these pests are consumed by common desert predator species under lab conditions, suggesting that they could subsidize desert communities. Results showed differences in composition between the communities nearest the crop area and those at the greatest distance, but the changes were not related to distance from the crop area. Predator abundance decreased with distance from the crop area, suggesting that predators may respond to the pest subsidy. Few other studies have shown such weak impact of subsidies of agricultural herbivores on natural habitats. In this study, prey spillover effects were noticeable on one group of predators (spiders), but not on the desert arthropod community overall. More studies over a longer time period and with greater temporal resolution should be conducted to examine the ecological consequences of both prey and predator spillover effects from agricultural areas to adjacent natural habitats.

Mots clés : Agricultural pests — Israel — Arabah Valley - Arid regions agriculture — Arthropoda — Habitat (Ecology) — Case studies — Arthropod populations — Effect of habitat modification on — Israel — Arabah Valley

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Page publiée le 12 novembre 2016, mise à jour le 21 novembre 2018