1. THE RELATIONSHIP BETWEEN MACULINEA ALCON (DENIS & SCHIFFERMÜLLER) AND SELECTED HABITAT VARIABLES: A MULTIVARIATE APPROACH
Soares, P.1, Crespi, A.2, Torres, L.1, Arnaldo, P.1
1 Departamento de Protecção de Plantas, Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, Vila Real, Portugal.
2 Departamento de Engenharia Biológica e Ambiental, Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, Vila Real, Portugal.
Introduction
The blue alcon, Maculinea alcon (Denis & Schiffermüller), is one of the most endangered butterflies in Europe (Munguira & Martin 1999) and its population is in decline, with localised extinctions in many countries (Wynhoff 1998; Van Swaay &Warren 1999). The most important factors that lead to decline are biotope losses, fragmentation of habits in biotope remnants and worsening habitat quality, especially in wet and poor nutrient biotopes (Maes & Van Dyck 2001). In Portugal, M. alcon is the only representative of its genus, being one of the rarest of our native butterflies. This paper reports a multivariate analysis of the relationship between the blue alcon and selected habitat variables aimed at determining biotope preferences.
Material and Methods
The study was conducted in a wetland located in the Alvão Natural Park. Three habitats were distinguished in terms of covering vegetation: Habitat A, grass cover > 60%; Habitat B, ferns cover > 40% and Habitat C, shrub cover > 50%. For data collection, 20 plots of 16 m2 (total area of about 320 m2) were marked out at each habitat and the following parameters were registered: number of gentians (NG), density of gentians (DG), number of stems by plant (NS), number of flower buds per plant (NB), and plant height (Alt). Oviposition of M. alcon was recorded by counting the number of eggs per gentian (NE) within each plot, the number of gentians with eggs (NGE), the number of eggs per stem (NES) and the density of egg batches (DE). For ant assemblage, the number of nests (N) was noted within the selected plots. To group the three habitats under examination, a cluster analysis was performed. To analyze the relationship between the habitat variables and Maculinea occurrence, Classified PCA and CDA were performed. Finally, to establish the variability of each parameter, the boxplot representation was employed.
Results
The classification analysis suggests that there is no apparent correlation between DG, NG, NB, N and NE. In contrast, Alt is the only floristic parameter correlated with the Maculinea butterflies, NE and N (Fig. 1). CDA procedure yielded three plant size classes: Class1 - less than 20 cm high; Class 2 – between 20 cm and 25 cm high and Class3 – higher than 25 cm (Fig. 2).
Fig. 1- PCA representation for the entire set of selected variables.
Fig. 4 - CDA of the structural matrix organized per habitat, and mean plots for the most discriminate variables (NG, NE, Alt, NB and N) per type of habitat
Fig. 2 - CDA analysis for the entire matrix classified into three size classes: less than 20 cm (Class 1), between 20 cm and 25 cm (Class 2) and higher than 25 cm (Class 3) - has revealed the most discriminate classification of the data collected (F=16,691, p-level=0,000).
Fig. 3 - Narrow variability for N, NE and Alt indicates a high significance for mean comparisons
The relationship between floristic and faunistic parameters and the structure of the habitat shown in the CDA plots of the Fig.4. This data allows us to conclude that NG is the most discriminate variable. Based on these results, contrasting behavioural patterns have been detected between NG and NE, Alt and N.
The boxplot of Fig.3 demonstrates the very limited variability existing for N, NE and Alt, in contrast with that found for NG and NB. This implies that the results obtained per habitat for the former groups of variables (i.e., N, NE and Alt) will expose less dispersion and, consequently, more significance.
Discussion
The vegetational structure has revealed the importance of determining NG and Alt of G. pneumonanthe. Here, three different structures of wetlands were selected, in a bid to determine the most appropriate habitat for supporting M. alcon individuals. The results obtained highlight low correlations between NB, N and NE. Positive correlations were observed, however, for Alt, N and NE. While these results are in perfect agreement with those of Van Dyck et al. (2000), they contrast with those of other authors (Dolek et al. 1998; Nowicki et al. 2005). Moreover, negative correlations were derived for NG and NE, as shown by F. Kéry et al. (2001), who suggested positive relationships between population size and NE, for G. cruciata and M. rebeli. These results will be decisive for future conservation tasks.
References
Munguira M L & Martin J (1999) Action Plan for Maculinea Butterflies in Europe. Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention), Nature and Environment, 97, Strasburg: Council of Europe Publishing.
Maes D & Van Dyck H (2001) Butterfly diversity loss in Flanders (north Belgium): Europe’s worst case scenario? Biological Conservation 99:
Van Swaay C A M &Warren M S (1999) Red Data Book of European Butterflies (Rhophalocera). Nature and Environment, 99. Council of Europe Publishing, Strasbourg.
Wynhoff I (1998) The recent distribution of the European Maculinea species. J. Insect Conservation, 2: