Responses of Etiella zinckenella to habitat fragmentation of Caraganas in desert steppe in Ningxia, China

Habitat fragmentation is a common cause for which species becomes threatened or endangered. Existence of viable habitat is critical to the survival of any species, so habitat fragmentation is the main reason for the changes in distribution and abundance of organisms, and is usually considered to have negative effect on the abundance, species richness and population of organisms in a specific landscape. But this effect may also depend on whether some species could use one or more types of habitat in a specific landscape. Because of its well resistance to stress, Caragana is one of predominant shrub in desert region for forest planting and desert preventing, which plays a critical role in desert control and ecosystem stabilization. Baijitan National Nature Reserve, located in Lingwu County, Ningxia Hui Autonomous Region, China, is typical of desert nature reserve in which the Caragana spp., Oxytropisaciphylla and other desert plants are protected. The Caragana woodlands in this region show a pattern of dots, patches and strips separated by natural and cultivated forest, thereby leading to a typical fragmented landscape. Etiellazinckenella (Lepidoptera, Pyralidae) is one of seed pests of Caragana. In order to illuminate the responses of E. zinckenella to the habitat fragmentation of Caraganas woodlands, the present study focused on the effects of habitat area, habitat fragmentation, as well as matrix composition on the population density and damage ratio of E. zinckenella in desert steppe. From May 2008 to June 2009, by using parallel jump sampling method, 13 Caragana woodland patches representing four landscapes from Baijitan National Nature Reserve were investigated and totally 15,117 pods were inspected. Then, the landscape fragmentation indices, population density and damage ratio of E. zinckenella in Caragana woodlands were calculated. The statistic analysis of the data indicated that the four landscapes have a significant difference in the population density and damage ratio of E. zinckenella; and in the same landscape, the neighbor patches also have a significant difference in the damage ratios of E. zinckenella. E. zinckenella seems to prefer some species of Caragana, for instance, the damage ratio of E. zinckenella to Caragana microphylla is found the highest, followed by the damage ratio to Caraganadavazamcidamage, while the damage ratio to Caraganakorshinskii is found the lowest. The coverage of Caragana is found positively related to the damage ratio of E. zinckenella with hinge damage ratio in high coverage of Caragana forest. The regression analysis shows that the latitude (R_s = 0.5724), longitude (R_s = 0.5577), altitude (R_s = 0.4614) and patch area (R = 0.3012) were not significantly associated with population density and damage ratio of E. zinckenella. However, the population density and damage ratio of E. zinckenella decreased with the increasing in patch area. The landscape patch fragmentation index (R = 0.91129) and the patch density index (R = 0.89864) show a positive correlation with damage ratio. The fragmentation shape index (R = ?0.89675) and inside habitat area fragmentation index (R = ?0.77646) show a negative correlation with the damage ratio. As a result, the population of E. zinckenella was suppressed by the landscape fragmentation, but the patch isolation and complementary resources in the landscape matrix may also have a positive impact on the population density of E. zinckenella.