Beyond Cladistics: The Branching of a Paradigm

6. Island Hot Spots: The Challenge of Climate Change

91 SI X David Bramwell ISLAND HOT SPOTS The Challenge of Climate Change Biodiversity hot spots hold especially high numbers of endemic species, yet their combined area of remaining habitat covers only 2.3 percent of the Earth’s land surface. Each hot spot faces extreme threats and has already lost at least 70 percent of its original natural vegetation. Over 50 percent of the world’s plant species and 42 percent of all terrestrial vertebrate species are endemic to the thirty-four biodiversity hot spots (Conservation International Web site 2008). Islands are of particular importance in a biodiversity conservation context as they cover about 5 percent of the Earth’s land surface but have more than 35 percent of the world’s vascular plants including about fifty thousand endemics. At the same time, about 15 percent of the world’s mammals, amphibians, and birds are exclusively insular in distribution, and 35 percent of all threatened birds are island endemics In fact, of the thirty-four biodiversity hot spots defined by Myers et al. (2000) and refined by Conservation International in 2005, fourteen are islands or island archipelagos or have an important insular component, and six others include offshore islands within their limits. These include such hot spots as New Zealand, Polynesia/Micronesia, Madagascar and the Indian Ocean islands, the Caribbean Islands, the Philippines (with over seven thousand islands), the Mediterranean Basin including Macaronesia (the hot spot was recently expanded to include the Azores Beyond Cladistics: The Branching of a Paradigm, edited by David M. Williams and Sandra Knapp.Copyright byTheRegentsoftheUniversityofCalifornia.Allrightsofreproduction in any form reserved. 92 / BOTANY and Cape Verde Islands), the Valdivian forests of Chile now including the Juan Fernández Islands, and the Galápagos Islands included in the Tumbes/Chocó continental hot spot, among others. It seems, however, to make little sense to subordinate these last three archipelagos to mere appendices of continental hot spots especially as their high endemicity means that they generally have little in common with the adjacent continents in terms of their unique biodiversity. Island organisms have always been especially vulnerable to human activities, from the extinction of flightless birds such as the dodo through overhunting, the destruction of natural vegetation for agricultural exploitation (e.g., the sugar cane industries in the Canaries and Mauritius), urban development especially for tourism, or the more subtle threat of competition from invasive, introduced alien species. Since human arrival on islands, the native species have always been up against it. And now, because of human-induced climate change they face further threatening challenges including a rise in sea level of, according to recent estimates, between 2 and 15 meters in the next 100 years (Geo-Arizona Web site 2007). Although generally the lowest islands are not rich in endemic biodiversity, it is still a pity to lose them! Apart, however, from being covered by water, we have to ask the question, What makes insular organisms and, in the context of this chapter, insular plants so vulnerable? CARLQUIST’S ISLAND SYNDROME Over 35 years ago,Sherwin Carlquist,in his book Island Biology (Carlquist 1974) defined a series of characteristics common to many organisms from islands throughout the world as the island syndrome. This syndrome includes such phenomena as woodiness and longevity in generally herbaceous groups of plants and gigantism in animals, reduction of dispersal capacity through enlarged seeds, diminished efficiency of dispersal mechanisms such as a depauperate pappus in plants of the Asteraceae , and the loss of flight capacity in birds and insects. The obvious tendency for island plants to be poor competitors in the face of invasive species is also considered to be one of the syndrome’s characteristics. The island syndrome includes adaptation to narrow, specific ecological niches through what Carlquist considered to be an irreversible specialization leading to a major ecological shift from the original colonizer, including the need to adapt to new pollinators especially as many islands I SLAND HOT SPOT S / 93 do not have rich pollinating insect faunas. Spencer Barratt, in an important review of reproductive biology of island plants, cites as examples the depauperate insect fauna of the Hawaii archipelago with only six moth species, two butterflies, and two bumblebees, and the Galápagos Islands with only one pollinating bee (Barratt 1998). The strong trend to obligate outcrossing through dioicy and gynodioicy , the so-called escape from homozygosity, also seems to qualify as part of the island syndrome...