Reproductive performance of Helianthemum caput-felis along its fragmented distribution in the Mediterranean coasts

Plant's reproductive success is determined by intrinsic characteristics of the reproductive system of the species, as well as by extrinsic abiotic and biotic factors. Reproductive traits can vary along different gradients (e.g. ecological, geographical, etc.) and several studies revealed that the most favourable conditions (i.e. greater densities, fitness and genetic diversity) will be found at the core of a plant distribution range than in marginal or isolated populations. In this study the phenological and reproductive traits of several fragmented populations of Helianthemum caput-felis Boiss. (Cistaceae), a perennial Mediterranean plant were investigated. Six populations, covering the entire distribution range of the species were studied over two years (2013–2014). The phenology and reproductive outputs were analysed considering ecological and climatic factors, and human trampling intensity by fitting Generalised Linear Mixed Models (GLMMs). The results indicated that geomorphology, substrate, slope and human trampling intensity affected the reproductive traits of H. caput-felis. An ecological gradient, mainly linked by the interaction of temperature and precipitation regimes could explain this finding. Plants growing at the eastern edge of the distribution range (Sardinia; geographically marginal) produced more fruits than those growing in the other populations. Conversely, plants growing in arid substrate showed a negative correlation with fruit production and viable fruits. The reproductive outputs of the populations located in the core of the distribution range (Cabo Roig and Moraira; ecologically marginal) were lower than those of the other populations. On the other hand an ecological gradient dominated by the precipitation and temperature regimes was detected. In addition, a positive effect of the high and moderate level of human trampling on the reproductive output was found. Further studies, based in particular on the habitat fragmentation, are needed to understand the complex interactions that govern the reproductive output of H. caput-felis in the Mediterranean region.