Trophic niche, age structure and seasonality in Dolichopoda cave crickets

Shifts in feeding habits are expected to occur during adaptation to cave life. Dolichopoda cave crickets inhabit both natural and artificial caves showing differences in population size, fecundity, phenology and age structure. Compared to artificial caves, typically holding a seasonal age structure, populations from natural caves maintain a constantly heterogeneous age structure. Faecal content analysis of 605 individuals from 24 natural and artificial cave populations, enabled us to characterize their trophic niche and to investigate its variation. The results of multivariate analyses and measures of niche breadth and niche overlap outlined differences in trophic resource exploitation between natural and artificial cave populations. Seasonal variation in diet occurred in both types of caves, and it was greater in artificial cave populations. However, within any season, differences in feeding habits between individuals were much greater in natural caves resulting in a wider heterogeneity in trophic resources exploitation. Such heterogeneity appears to be mainly due to differences in diet between individuals of different developmental stages. In fact, in a sample of 15 populations we found a positive, statistical significant correlation between niche breadth and heterogeneity in age structure. These data are discussed in a broader evolutionary context in order to understand the role of limited resources availability in shaping and maintaining heterogeneity in age structure of Dolichopoda populations.