Galapagos Islands: Increase in Introduced Plant Species and Invasive Species Distribution, Study notes of Plant Taxonomy and Evolution

Download Galapagos Islands: Increase in Introduced Plant Species and Invasive Species Distribution and more Study notes Plant Taxonomy and Evolution in PDF only on Docsity! 0 100 200 300 400 500 600 700 800 1535 1585 1635 1685 1735 1785 1835 1885 1935 1985 N u m b er o f i n tr o d u ce d p la n t sp ec ie s re co rd ed Year Galapagos Report 2006 - 2007 133 BIODIVERSITY AND BIOPHYSICAL RESOURSES Increase in the number of introduced plant species in Galapagos Alan Tyea, Rachel Atkinsona & Víctor Carriónb aCharles Darwin Foundation , bGalapagos National Park Year Cumulative number of introduced species1 Reference 1535 0 1807 2 Porter 18224 1837 23 Hooker 1847 5 1853 35 Andersson 1858 6 1899 65 Robinson 1902 7 1906 85 Stewart 19118 1970 166 Wiggins & Porter 19719 1986 271 Lawesson et al . 1987 10 1990 364 Mauchamp 19971 1995 404 Mauchamp 19971 1999 437 2000 453 2003 486 2006 748 CDF database: records to end of 1999 CDF database: records to end of 2000 CDF database: records to end of 2003 CDF database: records to end of 2006 Mauchamp1 charted the rise in the number of intro- duced vascular plant species (flowering plants and ferns) in the Galapagos Islands up to 1997. Since that time the number of introduced plants has continued to rise2. However, a more comprehensive analysis3 indi- cates that the rise in number of identified introduced plant species since the 1980s is not only due to recent introductions but also, in large part, due to an increase in interest in invasive plants and their impact on natural ecosystems, and thus the recent identification of species that were introduced in the past. The present report summarizes the previous data and brings the 1Excludes doubtfully native species3. The figures in this column sometimes differ from those quoted by the author cited (and from those cited in Tye2), owing to reclassification or re-identification of some species, and to the addition of species reported by prior authors, some of which were overlooked by later authors. Figure 1. The cumulative number of introduced vascular plant species registered in Galapagos Table 1. Reports of introduced plant species in Galapagos. total number of introduced plant species known in Galapagos up to date. It also briefly examines the distribution of invasive plants on different islands. Data from Tye3 and the more recent records in the Database of the Galapagos Flora of the Charles Darwin Foundation (CDF) are presented in Table 1 and Figure 1. The recent records are largely a result of exhaustive surveys of the towns and agricultural areas of the four inhabited islands, which attempted to record all intro- duced plants on every parcel of land. Source: CDF Database Note Santiago Bartolomé Rábida Pinzón Baltra Fernandina Isabela Floreana Española San Cristóbal Santa Cruz Santa Fe Puerto Ayora INHABITED ZONES Introduced plants 502 420 197 412 Santa Cruz Isabela Floreana San Cristóbal The true rate of introduction-naturalization in Galapagos has been linear, although the graph may show exponential growth3. And despite the implemen- tation of quarantine controls in 1998, the rate is not yet declining. The number of cultivated species appears to have increased exponentially in recent years, but this is not necessarily due to an increase in introduction rate. Property owners interviewed as part of the study indicated that many of the recently registered species were brought to the islands many years ago but only recently recorded by botanists. The most aggressive invasive plant species are concen- trated in the inhabited islands (Table 2) and have not been introduced to the majority of the uninhabited islands. However, Santiago is an uninhabited island with several highly-invasive plant species. Following goat and pig eradication on Santiago, several invasive species, including Hill Blackberry (Rubus niveus), are spreading and there is an intensive effort by the Galapagos National Park and the CDF to eradicate them. A few of the most invasive species are still only found in small numbers in some of the inhabited islands. Two examples are the Curse of India (Lantana camara) in Isabela and Hemp Agave (Furcraea hexapetala) in Floreana. Eradication programs have recently been initiated to eliminate these species before they become a serious problem as they have on other islands in the archipelago. The apparent rate of increase is obviously affected by increased scientific interest in recent years in the intro- duction process, as well as increased sampling effort. Although the earliest botanists included cultivated species4,5,8, Wiggins & Porter9 did not. They only included naturalized species (introduced species that have become successfully established in the wild). Thus, the jump in numbers presented by Lawesson et al.10 was partly due to the re-inclusion of cultivated species. All major studies since Lawesson et al.10 have included both cultivated and naturalized species. The increases reported since 1987 were primarily due to surveys that were carried out specifically to record introduced plants. The large increase in 20012 was due to initial inaccurate estimates of an exhaustive survey of the agricultural zone of Santa Cruz. The figures are corrected in Table 1 and Fig. 1. The recent large increase up to 2006 resulted from the inclusion of the more complete analysis of this survey and from surveys of Puerto Ayora and of the towns and agricultural areas on Floreana and Isabela (Fig. 2). The field survey on San Cristóbal is complete but the results have not yet been fully analysed; new species from this survey have not been included in Table 1 and Fig. 1. After including the results from San Cristóbal, we expect the total list of introduced vascu- lar plants in Galapagos to be between 800 and 900 species, nearly twice that of the native flora (500 species). The list of introduced vascular plant species recorded in Galapagos has reached 748, many more than the 500 species of native flora. Source: CDF Database Galapagos Report 2006 - 2007134 BIODIVERSITY AND BIOPHYSICAL RESOURSES Figure 2. Map of the recent introduced plant surveys of the inhabited zones of Galapagos* Note: *Numbers in this figure are provisional.