Frontiers of Biogeography

Recent reviews have highlighted the dominance of vertebrates and plants in macroecological and biogeographical publications while invertebrates are underrepresented despite their global ecological relevance and vast diversity. We argue that although the study of invertebrate biogeography and macroecology has data limitations and thus lags behind in global research coverage, it has left a strong mark on the development of the discipline and has continuing potential to significantly shape its future. First, we detail how historical collecting and identification impediments caused decelerated progress at the macro-scale. Second, we show the quantitative impact of early invertebrate studies in contrast to lowered current representation. Third, we discuss ways in which authors, editors, and reviewers may foster invertebrate studies in macroecology. These include an honest appreciation of the value of study replication, of understudied but diverse taxa, and of the ecological traits that make invertebrates unique in comparison to vertebrates (e.g., wider array of life cycles, symbioses, and ecological niches), as well as the expanded potential for experimentation and manipulation.

Vast amounts of Primary Biodiversity Data exist online (~10⁹ records, each documenting an individual species at a point in space and time). These data hold immense but unrealized promise for science and society, including use in biogeographic research addressing issues such as zoonotic diseases, invasive species, threatened species and habitats, and climate change. Ongoing and envisioned changes in biodiversity informatics involving data providers, aggregators, and users should catalyze improvements to allow efficient use of such data for diverse analyses. We discuss relevant issues from the perspective of modeling species distributions, currently the most common use of Primary Biodiversity Data. Key cross-cutting principles for progress include harnessing feedback from users and increasing incentives for improving data quality. Critical challenges include: (1) establishing individual and collective stable unique identifiers across all of biodiversity science, (2) highlighting issues regarding data quality and representativeness, and (3) improving feedback mechanisms. Such changes should lead to ever-better data and increased utility and impact, including greater data integration with various research areas within and beyond biogeography (e.g., population demography, biotic interactions, physiology, and genetics). Building on existing pilot functionalities, biodiversity informatics could see transformative changes over the coming decade via a combination of community consensus building, coordinated efforts to justify and secure funding, and technical innovations.

Ongoing work shows that species richness patterns on volcanic oceanic islands are shaped by surface area changes driven by longer time scale (>1 ka) geological processes and natural sea level fluctuations. A key question is: what are the rates and magnitudes of the forces driving spatial changes on volcanic oceanic islands which in turn affect evolutionary and biogeographic processes? We quantified the rates of surface-area changes of a whole island resulting from both volcanogenic flows and sea level change over the last glacial-interglacial (GI) cycle (120 ka) for the volcanically active island of Terceira, (Azores, Macaronesia, Portugal). Volcanogenic activity led to incidental but long-lasting surface area expansions by the formation of a new volcanic cone and lava-deltas, whereas sea level changes led to both contractions and expansions of area. The total surface area of Terceira decreased by as much as 24% per time step due to changing sea levels and increased by 37% per time step due to volcanism per time step of 10 ka. However, while sea levels nearly continuously changed the total surface area, volcanic activity only impacted total surface area during two time steps over the past 120 ka. The surface area of the coastal and lowland region (here defined as area <300 m) was affected by sea level change (average change of 11% / 10 ka for 120–0 ka) and intra-volcanic change (average change of 17% / 10 ka for 120–0 ka). We discuss the biogeographic implications of the quantified dynamics, and we argue that surface area change is mainly driven by volcanic processes in the early stages of the island’s life cycle, while during the later stages, area change becomes increasingly affected by sea level dynamics. Both environmental processes may therefore affect biota differently during the life cycle of volcanic oceanic islands.

Understanding the influence of geographic features on the evolutionary history and population structure of a species can assist wildlife managers in delimiting genetic units (GUs) for conservation and management. Landscape features including mountains, low elevation depressions, and even roads can influence connectivity and gene flow among Agassiz’s desert tortoise (Gopherus agassizii) populations. Substantial changes in the landscape of the American Southwest occurred during the last six million years (including the formation of the Gulf of California and the lower Colorado River), which shaped the distribution and genetic structuring of tortoise populations. The area northwest of the Gulf of California is occupied by the Salton Trough, including the Coachella Valley at its northern end. Much of this area is below sea level and unsuitable as tortoise habitat, thus forming a potential barrier for gene flow. We assessed genetic relationships among three tortoise populations separated by the Coachella Valley. Two adjacent populations were on the east side of the valley in the foothills of the Cottonwood and Orocopia mountains separated by Interstate 10. The third population, Mesa, was located about 87 km away in the foothills of the San Bernardino Mountains at the far northwestern tip of the valley. The Cottonwood and Orocopia localities showed genetic affiliation with the adjacent Colorado Desert GU immediately to the east, and the Mesa population exhibited affiliation with both the Southern Mojave and Colorado Desert GUs, despite having a greater geographic distance (0.5x–1.5x greater) to the Colorado Desert GU. The genetic affiliation with the Colorado Desert GU suggests that the boundary for that GU needs to be substantially extended to the west to include the desert tortoise populations around the Coachella Valley. Their inclusion in the Colorado Desert GU may benefit these often overlooked populations when recovery actions are considered.

The Atacama Desert harbors a unique arid-adapted flora with a high degree of endemism, the origin of which is poorly understood. In the Atacama Desert, Zygophyllaceae is represented by five endemic species: one member of Zygophylloideae: Fagonia chilensis; and four members of Larreoideae: Bulnesia chilensis and Porlieria chilensis, the only representatives in the Atacama Desert of genera with disjunct distributions between Argentina, Peru and Chile; and monotypic endemic genera Metharme lanata and Pintoa chilensis. Zygophyllaceae are thus a particularly suitable group for studying the historical assembly of the Atacama Desert flora as each of these species may represent independent biogeographical events. We made use of published as well as original plastid DNA sequences (rbcL, trnL-trnF & trnS-trnG) to reevaluate the phylogenetic relationships of the Atacama Zygophyllaceae. Bayesian divergence time estimates as implemented in BEAST2 and ancestral area reconstruction with the Dispersal Extinction Cladogenesis approach using BioGeoBEARS were applied to infer ancestral ranges. We compiled the most complete data set of Larreoideae to date with 25 of 28 species. Bulnesia rivas-martinezii from Bolivia forms a clade with Pintoa chilensis from the Atacama Desert, rendering the genus Bulnesia paraphyletic. Most representatives of Zygophyllaceae colonized the Atacama Desert during the Miocene, and only Fagonia dispersed more recently. The colonization history of the Atacama Desert in South America is reflected by three individual distribution patterns or floristic elements. The presence of Bulnesia, Pintoa, and Metharme is best explained by Andean vicariance, while the southern Atacama Desert representative, Porlieria chilensis, has a continuous distribution into central Chile from where it probably dispersed further north. The only South American Fagonia species (F. chilensis) likely colonized the Chilean-Peruvian Coastal Desert via long distance dispersal from North America.

Advances in high throughput genomic approaches are enabling the accurate appraisal of movements of diverse species, previously considered intractable. The impact of long-distance dispersal and distribution changes on species interactions (such as host-parasite interactions) is of particular importance as attempts are made to project how ecosystems will shift under environmental change. The sub-Antarctic region, comprising isolated islands separated by hundreds to thousands of kilometres of open ocean, presents an ideal model system for studying long-distance dispersal, distribution, and ecosystem change. Here we used genomic methods to determine the extent of movement of penguin ticks (Ixodes uriae) among different host species, and among penguin colonies at small (within an island) and large (among islands separated by >6000 km) scales, in the sub-Antarctic region. Our results suggest that I. uriae ticks may be readily shared between distantly related penguin species with similar phenology, but indicate that – as inferred by previous research – ticks are less likely to be shared between flighted and non-flighted sea- birds. We also find evidence for small-scale movements of penguin ticks with their hosts, but no evidence for movements between islands separated by thousands of kilometers of open ocean. These inferred limitations to penguin tick movement could be the result of restricted host movements or the inability of penguin ticks to survive extended trips at sea. Our findings help elucidate parasite-host dynamics, with implications for host health and persistence in a region experiencing rapid environmental change.

Speciation is thought to be predominantly driven by the geographical separation of populations of the ancestral species. Yet, in the marine realm, there is substantial biological diversity despite a lack of pronounced geographical barriers. Here, we investigate this paradox by considering the biogeography of marine mammals: cetaceans (whales and dolphins) and pinnipeds (seals and sea lions). We test for associations between past evolutionary diversification and current geographical distributions, after accounting for the potential effects of current environmental conditions. In general, cetacean lineages are widely dispersed and show few signs of geographically driven speciation, albeit with some notable exceptions. Pinnipeds, by contrast, show a more mixed pattern, with true seals (phocids) tending to be dispersed, whereas eared seals (otariids) are more geographically clustered. Both cetaceans and pinnipeds show strong evidence for environmental clustering of their phylogenetic lineages in relation to factors such as sea temperature, the extent of sea ice, and nitrate concentrations. Overall, current marine mammal biogeography is not indicative of geographical speciation mechanisms, with environmental factors being more important determinants of current species distributions. However, geographical isolation appears to have played a role in some important taxa, with evidence from the fossil record showing good support for these cases.

The beautiful Rockhopper penguin colonies of Murrell Island (Falkland Islands). You can learn about the dispersal of ticks (Ixodes uriae) in penguin colonies of these sub-antaractic islands in an article by Moon, Chown and Fraser in this issue of Frontiers of Biogeography. Picture by Katherine L. Moon.