Herbivory and plant competition effects on the population dynamics of Naufraga balearica, a threatened narrow endemic species of the Balearic Islands

Abstract

Naufraga balearica is a caespitose member of the Umbelliferae and is endemic to Majorca. We conducted a 12-year study in which permanent plots were monitored (each plot was divided into 100 cells) to assess (1) the natural population dynamics, (2) goat herbivory (1998–2003) and (3) plant competition. Using photographs and a G-test of independence, we analysed the frequency of cells in which a species was present and, for each annual transition, the frequency of cells where the species was stable, decreased or increased for each species and treatment (plots open to herbivores vs. closed plots). The natural dynamics of this threatened species showed a clear decline at the study site. Dactylis glomerata and Erodium reichardii were the species that appeared to have the greatest effect on the presence of N. balearica, especially in the closed plots. The competition effect of neighbouring species was not homogeneous throughout the 11 annual transitions analysed, suggesting that other factors affect the dynamics of the threatened species. Some herbivory pressure is beneficial to N. balearica because the species fluctuates more in the opened plots and the behaviour of the goats helps to control competing species, permitting the establishment of N. balearica.

Keywords:

• Plant-animal interactions
• herbivory pressure
• competing species
• caespitose plant
• rare species

Acknowledgements

We thank Dr. John D. Thompson (Centre d'Ecologie Fonctionnelle et Evolutive, CNRS, Montpellier) for statistical advice and for his comments on the draft of the manuscript. We also thank José María Castro and Antoni Mateu for their collaboration in the fieldwork. For this research, J. Cursach received a grant from the Conselleria d'Economia, Hisenda i Innovació del Govern de les Illes Balears.