The West Indies as a laboratory of biogeography and evolution

Abstract

Islands have long provided material and inspiration for the study of evolution and ecology. The West Indies are complex historically and geographically, providing a rich backdrop for the analysis of colonization, diversification and extinction of species. They are sufficiently isolated to sustain endemic forms and close enough to sources of colonists to develop a dynamic interaction with surrounding continental regions. The Greater Antilles comprise old fragments of continental crust, some very large; the Lesser Antilles are a more recent volcanic island arc, and the low-lying Bahama Islands are scattered on a shallow oceanic platform. Dating of island lineages using molecular methods indicates over-water dispersal of most inhabitants of the West Indies, although direct connections with what is now southern Mexico in the Early Tertiary, and subsequent land bridges or stepping stone islands linking to Central and South America might also have facilitated colonization. Species-area relationships within the West Indies suggest a strong role for endemic radiations and extinction in shaping patterns of diversity. Diversification is promoted by opportunities for allopatric divergence between islands, or within the large islands of the Greater Antilles, with a classic example provided by the Anolis lizards. The timing of colonization events using molecular clocks permits analysis of colonization-extinction dynamics by means of species accumulation curves. These indicate low rates of colonization and extinction for reptiles and amphibians in the Greater Antilles, with estimated average persistence times of lineages in the West Indies exceeding 30 Myr. Even though individual island populations of birds might persist an average of 2 Myr on larger islands in the Lesser Antilles, recolonization from within the archipelago appears to maintain avian lineages within the island chain indefinitely. Birds of the Lesser Antilles also provide evidence of a mass extinction event within the past million years, emphasizing the time-heterogeneity of historical processes. Geographical dynamics are matched by ecological changes in the distribution of species within islands over time resulting from adaptive radiation and shifts in habitat, often following repeatable patterns. Although extinction is relatively infrequent under natural conditions, changes in island environments as a result of human activities have exterminated many populations and othersespecially old, endemic species-remain vulnerable. Conservation efforts are strengthened by recognition of aesthetic, cultural and scientific values of the unique flora and fauna of the West Indies.

Frontier mutualism: coevolutionary patterns at the northern range limit of the leaf-cutter ant–fungus symbiosis

“…Cuba, as part of the proto-Greater Antilles, moved through the gap between North and South America at the end of the Cretaceous (over 60 Myr ago) and may have temporarily abutted what is now Southern Mexico [17,56]. Since the early Tertiary, however, Cuba is thought to have remained separate from the mainland and without temporary land-bridges during changes in sea levels [17,56].…”

“…Cuba, as part of the proto-Greater Antilles, moved through the gap between North and South America at the end of the Cretaceous (over 60 Myr ago) and may have temporarily abutted what is now Southern Mexico [17,56]. Since the early Tertiary, however, Cuba is thought to have remained separate from the mainland and without temporary land-bridges during changes in sea levels [17,56]. In the absence of gene flow across the ocean between mainland and Cuba, the Attamyces populations in Cuba, therefore, should have become genetically differentiated from the mainland populations, a prediction that is not supported by the observed population-genetic patterns (figure 1).…”

“…In the Northern Hemisphere, Atta texana reaches 338 N latitude in north-central Texas and northeastern Louisiana [15; this study] and Acromyrmex versicolor reaches almost 368 N latitude in northwestern Arizona [16]. It is unknown whether leaf-cutter ants dispersed into the North American continent before or after the closing of the Isthmus of Panama approximately 1-3 Myr ago [17]. However, leafcutter ants must have reached their current latitudinal limit in the southern USA sometime during the past 10 000 years following the most recent Pleistocene glaciation.…”

Are islands the end of the colonization road?

“…For example, frogs and lizards relocate by rafting [41,42]. Colonization of the West Indies by reptiles and amphibians from continental areas of the Caribbean Basin has been infrequent, at intervals of perhaps 0.75 My judging from age distributions of island lineages [43,44]. Many of the recolonizers, including some birds, have not dispersed further within island archipelagos, even though a member of the clade was able to colonize a continental landmass.…”

The flower plants introduced in the Lesser Antilles: Martinique’s example (general summary of the key data and ecosystem impacts

“…As a result, there are as many factorial constraints as there are island systems. To this fact we add the intra-island complexity that can still generate subdivisions (in terms of factorial sub-spaces) defining the large potential floristic, physiognomic and landscape groups, repeatedly described in the literature [32][33][34][35][36][37][38][39][40].…”