Conceptual and empirical advances in Neotropical biodiversity research

Abstract

The unparalleled biodiversity found in the American tropics (the Neotropics) has attracted the attention of naturalists for centuries. Despite major advances in recent years in our understanding of the origin and diversification of many Neotropical taxa and biotic regions, many questions remain to be answered. Additional biological and geological data are still needed, as well as methodological advances that are capable of bridging these research fields. In this review, aimed primarily at advanced students and early-career scientists, we introduce the concept of "trans-disciplinary biogeography," which refers to the integration of data from multiple areas of research in biology (e.g., community ecology, phylogeography, systematics, historical biogeography) and Earth and the physical sciences (e.g., geology, climatology, palaeontology), as a means to reconstruct the giant puzzle of Neotropical biodiversity and evolution in space and time. We caution against extrapolating results derived from the study of one or a few taxa to convey general scenarios of Neotropical evolution and landscape formation. We urge more coordination and integration of data and ideas among disciplines, transcending their traditional boundaries, as a basis for advancing tomorrow's ground-breaking research. Our review highlights the great opportunities for studying the Neotropical biota to understand the evolution of life.

Keywords: Biodiversity; Biogeography; Biotic diversification; Community ecology; Landscape evolution; Phylogenetics; Phylogeny; Phylogeography; Scale; Tropics.

Figure 1. The giant Neotropical puzzle.

Map of the Neotropical region, spanning from Central Mexico to central Argentina (red dashed line) and including all Caribbean Islands. The figure shows examples of the large diversity of Neotropical habitats and the taxa that inhabit those habitats. We also outline a few of the many topics in Neotropical biodiversity that can be studied in the “trans-disciplinary biogeographic approach” advocated here. (A) Eastern slopes of the Bolivian Andes, where the Amazonian and Andean biotas meet; (B) Patagonian mountains of southern Chile, which despite being in the temperate zone of South America is home to many Neotropical-derived lineages; (C) Iguazu waterfalls, where increased humidity create gallery forests within the South American open diagonal; (D) Southern grasslands of the Pampas, a naturally open habitat now largely influenced by human activity; (E) One of the ca. 338 known species of hummingbirds, a conspicuous clade currently restricted to the American continent and particularly diverse in the Andes; (F) Epidendrum ibaguense, a widespread species in the orchid family in which many new Neotropical species are discovered each year; (G) An unidentified fly in the inselbergs of southern French Guiana, where basaltic rocks emerge several hundred meters above the surrounding Amazonian rainforest; (H) The large dogtooth characin fish Hydrolycus scomberoides, exemplifying the world’s richest ichthyofauna in the Amazon drainage basin; (I) Ameerega flavopicta, a rock-dwelling frog species adapted to a region of high seasonality of precipitation; (J) A columnar cactus of central Mexico, near the northwestern limits of the Neotropical region where low-canopy forests and succulent vegetation build vegetation mosaics across the landscape. Map generated through the remote-sensing ESA GlobCover 2009 project and colored by biome assignments (©ESA 2010 and UCLouvain; http://due.esrin.esa.int/page_globcover.php). Photo credits: A–G, I and J: A.A.; H: J.A.

Figure 2. Taxonomic sampling across the world’s tropics.

Density maps for geo-referenced species occurrences available from the Global Biodiversity Information Facility for (A) Mammals, (B) Amphibians, (C) Fishes, (D) Vascular plants between the Tropics of Cancer and Capricorn (23.5°S–23.5°N), showing the main spatial biases of taxonomic sampling. All datasets were cleaned for automatically detectable errors using SpeciesGeoCoder (Töpel et al., 2016). The figure is shown on a cylindrical equal area projection with standard parallels of 11.75°S and 11.75°N. The width of each cell is consistently 1°, while the height of each cell is 1° at the standard parallels, slightly lower at the equator and slightly higher at the Tropics of Cancer and Capricorn. Colors indicate 10-based logarithm of the number of records.

Figure 3. The complex topography and geology of South America.

This map highlights the topographic differences across the continent, including the Precambrian and Paleozoic upland shields, and the Andean cordilleras and structural arches that uplifted during the Cretaceous and Cenozoic. The Sub-Andean foreland basin constituted the main drainage axis of South America for most of the past 100 million years, serving as the main arena of evolutionary diversification for the mega-diverse biota of lowland Amazonia. Uplift of structural arches during the Paleogene and Neogene resulted in the formation of the modern continental drainage configuration. Base map created by Paulo Petry from the Shuttle Radar Topography Mission with elevations in meters. Note that the scale exaggerates differences at lower elevations. Adapted from Albert, Petry & Reis (2011).

Figure 4. Heat map summarizing the current (right upper boxes) and potential (left bottom boxes) interactions across the biodiversity disciplines in the Neotropics.

The X- and Y-axes indicate the typical taxonomic and temporal scales covered by each discipline, respectively. The white text in each box provides some short examples of why the disciplines are not yet successfully integrated, and some of the key benefits that will be gained by a further integration. See text for a discussion.

Figure 5. Main evolutionary and ecological processes contributing to the formation of species richness.

The regional species pool (light gray box) is defined as the sum of all the local species assemblages (darker gray box). Black arrows indicate processes that increase species richness, red arrows processes that reduce species richness. Note the hierarchical organization of processes resulting in species richness, with evolutionary processes occurring over regional to continental spatiotemporal scales and ecological processes occurring over local scales. Speciation and dispersal contribute new species to the regional pool, while extinction removes species. Dispersal mediated by abiotic habitat filtering and biotic facilitation (Kraft & Ackerly, 2014) increase the richness of local assemblages by enhancing establishment of species preadapted to local conditions, or aiding in the establishment of other species. Biotic interactions such as predation and competition may serve to reduce local richness. Diagram modified from Schluter & Ricklefs (1993) and Albert, Val & Hoorn (in press).