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| Minimum Area of Suitable Habitat (MASH) and Minimun Viable Population (MVP) were two
important aspects in Population Viability Analysis (PVA). MASH for a viable population can be estimated in several ways. The density-area method estimated MASH as the smallest area in which population can survival for a long time and variation was below 0.05. We used a variant of density-area method to study MASH for aphids, parasitoids, and hyperparasitoids in Northwest of China, where wheat was a main crop in agriculture. The variant was based on the premise that individuals within populations were likely to occur at usually high densities variation when confined to small areas and it
estimated MASH as the smallest area beyond which density plateaus. For all 72 sites, aphids,
parasitoids and hyperparasitoids occurred in all sites because wheat fields were highly homogeneous. We found that a consistant inverse density-area relationship was present over smaller areas, but different species had different function, especially in different trophic level. MASH of M. avenae, S. graminum, A. avenae, A. gifuensis, A. sp.1 and P. aphidis estimated from density-area relationship were
260, 240, 510, 490, 950, and 990m2 respectially. Results of inverse proportion function according to which MASH of M. avenae, S. graminum, A. avenae, A. gifuensis, A. sp.1 and P. aphidis were 310, 286, 543, 492, 952, and 1003 m2 respectially were similar to that of density-area relationship. We concluded that a negative density-area relationship may be an inevitable consequence of agricultural intensification and farmland fragmentation. We also concluded that different species may have different MASH requirement in agricultural landscape according to body size, migration, trophic level,
and habitat quality, which could interpret the phenomenon that highest percent parasitism was always in 800-1000 m2 wheat fields which exceeded MASH of parasitoids and suppressed activity of hyperparasitoids . Finally, we concluded that the value of any MASH as a pest control tool was compromised in Conservation Biological Control (CBC). |
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| Keywords:Minimum Amount of Suitable Habitat (MASH);Population viability Analysis (PVA);Parasitoid;Hyperparasitoid; Landscape;Conservation biological control (CBC) |
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