Abstract: We studied the impact of habitat quality factors on the metapopulation structure and distribution, and thus the persistence of two species of melitaeine butterflies, Melitaea phoebe and Euphydryas aurinia, on a metapopulation scale in Chicheng County, Hebei Province, China. These two species coexist in a network of discrete habitat patches within a range of 10 km², larvae feeding on their specific host plants Stemmacantha uniflora (Compositae) and Scabiosa tschiliensis (Dipsacaceae) respectively. However, their nectar resources are almost the same during the adult flight period. The main flight period for E. aurinia is about one month earlier than M. phoebe, with an overlap of only about seven days. The host plants of these two melitaeine butterflies also have a great impact on their occurrence, but act in different ways. Density of the host plant has a great effect on the occurrence of M. phoebe, whereas the height of the host plant is important for E. aurinia. The abundance and distribution of nectar resources are positively correlated to the abundance and distribution of the two butterfly species. The vegetation diversity, evenness, and cover correlate negatively with the occurrence of E. aurinia, but not related to M. phoebe, while the vegetation height has a positive effect on the two butterfly species. We have also considered and discussed the impact of slope aspect, gradient, and irradiation of the habitat patches. Therefore, when discussing the factors affecting metapopulation structure and dynamics, we should pay attention not only to the patch size and Isolation but also the quality differences among patches. Four major points can be well concluded: 1) The specificity of larval host plants and the time segregation of adult feeding permit the co-existence of the two species in this small and patchy system. 2) The nectar resource is a major limiting factor and prone to being affected by weather stochasticity. The fluctuations in nectar resources can explain the dynamic rises and falls of these butterfly metapopulations from 1998 to 2000. 3) The differences between flight and food searching ability of the two butterfly species, as well as the differences between the features and spatial distribution of the two host plants species determined the different metapopulation structures of the two butterfly species. These results supported one of our former conjectures that E. aurinia is a classical metapopulation, and M. Phoebe is a source-sink metapopulation. 4) It is the spatial pattern and quality of the habitat patches (as determined by other factors, e.g., topographic features) interacting with the insects' behavior (e.g., plant preference and flight behavior) that determined the metapopulation structure and distribution of these two butterfly species.

Key words: Melitaeine butterflies, Melitaea phoebe, Euphydryas aurinia, metapopulation, habitat quality, host plant, nectar resources