A Rocha Portugal Observatory Report 2009-2010

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34 A Rocha Portugal Observatory Report 2009-2010 The following figures and tables aid a general comparison of species diversity in the Alvor Estuary area. Figures 4 and 5 show an overview of the total number of species and individuals recorded along transects in 1991, 2004 and 2009. Figure 4 Number of species recorded along transects in 1991, 2004 and 2009. Discussion Comparison with previous studies - 1991, 2004 and 2009 Figure 5 Number of individuals recorded along transects in 1991, 2004 and 2009, with the exception of P. Cecilia. From the outset, it was recognised that the results from this study would not be directly comparable to those from previous studies undertaken in the vicinity (Gardiner, 1992, Hayden & Carpenter 2005). Gardiner (1992) stated that the numbers recorded along the transects do not necessarily provide a realistic indication of butterfly species abundance on the rest of the Quinta. It was therefore to be expected that the species diversity and abundance of butterflies on the survey sites in Abicada and Mexilhoeira Grande would be different to those in Quinta da Rocha. It is important to remember that due to the different recording technique used in this study (see Methods) the relative number of species and individuals are likely to be higher in 2009 than in 2004 and 1991. There were a number of notable differences regarding the species identified across the surveys, as summarised in Table 4 below. An overview of species data from the three surveys within the comparable months (June-August) is provided in Table 1 of Appendix 3. Pieris brassicae (Large White) and Lasiommata megera (Wall Brown), for example, were not recorded in the 2009 survey. It is unlikely that these species were overlooked, but there is the possibility that this was the case with Pontia daplidice (Bath White) and Thymelicus lineola (Essex Skipper). Many of the skippers and whites were able to be caught and positively identified, however, many others were not and they were assumed to be the commoner species of their respective groups. This may be an explanation for the apparent disappearance of the latter two species in the locality.
Table 4 Differences of species recorded during the surveys Species Common name Presence 1991 (1 st Jun – 17 th Aug) Pontia daplidice Pieris brassicae Lasiommata megera Pyronia cecilia Thymelicus lineola Thymelicus acteon Bath white Recorded weekly in Quinta da Rocha Large white Present throughout – 134 records (all transects) Wall brown Recorded weekly in Quinta da Rocha Southern gatekeeper A Rocha Portugal Observatory Report 2009-2010 35 Present throughout – 149 records (all transects) Essex skipper Present until 22 nd Lulworth skipper June –107 records (all transects) Present until 6 th July – 47 records (all transects) Presence 2004 (1 st Jun – 17 th Aug) Present in July – 8 records (4 transects) Present until 6 th July– 23 records (5 transects) Sporadic records – 9 records (3 transects) Present throughout – 185 records (8 transects) Present until 29 th June - 14 records (4 transects) Present until 22 nd June – 15 records (4 transects) Presence 2009 (2 nd Jun – 19 th Aug) Not recorded Not recorded during the survey, 4 casual records on Quinta da Rocha Not recorded Present throughout - 280 records within 4 transects Not recorded Present until 30 th June – 60 records (4 transects) Seven of the species mentioned in the discussion (those underlined in the paragraphs below) are listed in the European Butterfly Indicator for Grassland species (Van Swaay and Van Strien, 2010), six of them reported to be in decline on a European scale. The status of Lasiommata megera (Wall Brown) being in “Steep decline” is most concerning and, although the results of the European Butterfly Indicator are mainly based on data collected in other countries, it suggests that the absence of this species in this 2009 survey could be analogous to the general trend in Europe. The structure, composition and abundance of vegetation within the survey areas are likely to have a major impact on the butterfly fauna. The vegetation on the Abicada peninsula is rather uniform when compared to that of the previous surveys undertaken on the Quinta da Rocha. It might, therefore, be expected that the number and diversity of butterflies would be less in this survey whilst acknowledging that many other variables may also apply. Other than extensive grazing, the majority of the Abicada headland had largely been agriculturally abandoned. The vegetation in the vicinity of the transects was mainly dry grassland with scattered fig, carob and olive trees (Transects A2, A3, M1). Unsurprisingly, the butterfly species that feed 2 on diverse grasses were the most numerous in those transects (Pyronia cecilia, Thymelicus acteon), along with other grassland species 3 that feed on various Fabaceae (Polyommatus icarus, Colias croceus), various Geraniaceae (Aricia cramera), various Malvaceae (Carcharodus tripolina), Phlomis purpurea (Muschampia proto) and Rumex acetosella (Lycaena phlaeas). Coenonympha pamphilus (Small Heath), have previously been observed on Quinta da Rocha but was never recorded in very high numbers. Maniola jurtina (Meadow 2 Feeding refers to the food plant of the caterpillars and not to the nectar source used by the adults 3 Butterfly species having grassland as their main habitat (Van Swaay and Van Strien, 2010) Trend ↘ ↘ ↘ ↗ ↘ ↗
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