Jonathan P. Price

Oceanic island biogeography through the lens of the general dynamic model: Assessment and prospect

The general dynamic model of oceanic island biogeography (GDM) has added a new dimension to theoretical island biogeography in recognizing that geological processes are key drivers of the evolutionary processes of diversification and extinction within remote islands. It provides a dynamic and essentially non‐equilibrium framework generating novel predictions for emergent diversity properties of oceanic islands and archipelagos. Its publication in 2008 coincided with, and spurred on, renewed attention to the dynamics of remote islands. We review progress, both in testing the GDMs predictions and in developing and enhancing ecological–evolutionary understanding of oceanic island systems through the lens of the GDM. In particular, we focus on four main themes: (i) macroecological tests using a space‐for‐time rationale; (ii) extensions of theory to islands following different patterns of ontogeny; (iii) the implications of GDM dynamics for lineage diversification and trait evolution; and (iv) the potential for downscaling GDM dynamics to local‐scale ecological patterns and processes within islands. We also consider the implications of the GDM for understanding patterns of non‐native species diversity. We demonstrate the vitality of the field of island biogeography by identifying a range of potentially productive lines for future research.

Modeling Hawaiian Ecosystem Degradation due to Invasive Plants under Current and Future Climates

Occupation of native ecosystems by invasive plant species alters their structure and/or function. In Hawaii, a subset of introduced plants is regarded as extremely harmful due to competitive ability, ecosystem modification, and biogeochemical habitat degradation. By controlling this subset of highly invasive ecosystem modifiers, conservation managers could significantly reduce native ecosystem degradation. To assess the invasibility of vulnerable native ecosystems, we selected a proxy subset of these invasive plants and developed robust ensemble species distribution models to define their respective potential distributions. The combinations of all species models using both binary and continuous habitat suitability projections resulted in estimates of species richness and diversity that were subsequently used to define an invasibility metric. The invasibility metric was defined from species distribution models with <0.7 niche overlap (Warrens I) and relatively discriminative distributions (Area Under the Curve >0.8; True Skill Statistic >0.75) as evaluated per species. Invasibility was further projected onto a 2100 Hawaii regional climate change scenario to assess the change in potential habitat degradation. The distribution defined by the invasibility metric delineates areas of known and potential invasibility under current climate conditions and, when projected into the future, estimates potential reductions in native ecosystem extent due to climate-driven invasive incursion. We have provided the code used to develop these metrics to facilitate their wider use (Code S1). This work will help determine the vulnerability of native-dominated ecosystems to the combined threats of climate change and invasive species, and thus help prioritize ecosystem and species management actions.

Natural history, biogeography, and endangerment of Hawaiian dry forest trees

We describe the floristic composition of Hawaiian dry forest trees and identify natural history characteristics and biogeographic variables that are associated with risk of endangerment. Hawaiian dry forests are comprised of 109 tree species in 29 families, with 90% of all species endemic, 10% indigenous, and 37% single-island endemics. Forty-five percent of Hawaiian dry forest taxa are at risk of endangerment. Dry forest taxa at risk have a significantly larger range size compared to taxa from other Hawaiian forest types. Dispersal mechanism was a significant predictor of a species occurrence in dry forest compared to other forest types based on logistic regressions clustered by lineage. Among dry forest taxa, hermaphroditic breeding systems, autochorous dispersal mechanisms, conspicuous flowers, and dry fruit were all more likely to be at risk of endangerment. When analyses were clustered by lineage using logistic regressions, only dispersal mechanism and flower size were significant predictors of risk and taxa with autochorous dispersal and conspicuous flowers were more likely to be at risk. The Big Island, Maui, Oahu, and Kauai all have remarkably similar numbers of dry forest taxa (63–65 species) and dry forest taxa at risk of endangerment. However, Big Island and Kauai have the highest number and percentage of single-island endemics. These results demonstrate patterns of endangerment specific to Hawaiian dry forests, the high levels of endangerment in this forest type, and the importance of prioritizing conservation in dry forest regions.

Overview of Habitat History in Subtropical Oceanic Island Summit Ecosystems

Abstract Summit ecosystems of oceanic islands constitute one of the most ephemeral and isolated ecosystems existing, harboring specific features that confer on their biota an outstanding distinctness. Summits are short-lived entities, being the last ecosystems to be constructed during the growth of the new oceanic island, and the first to vanish due either to island subsidence, island erosion, or both. Whereas their geological emergence/disappearance is controlled by the volcanic/erosion activity, Pleistocene glaciations in the past million years, by forcing the altitudinal shift of the timberline, have also likely created or destroyed summit ecosystems, enabling the appearance of alpine ecosystems during glacial maxima where they were not present in interglacial periods and vice versa. On the other hand, summit ecosystems constitute islands within islands, being more isolated from climatically similar ecosystems than the coastlines of the islands containing them. Thus summit biota, frequently displaying a high endemicity, may originate either through dispersal from other close summit ecosystems during peak periods, or from the colonization of the summits and later evolution to the new conditions from mid-altitude species of the same island. Conversely, if peak periods are absent, the disappearance of summit ecosystems implies the extinction or extirpation of their constitutive species. Current summit species have likely occupied a much larger area during glacial periods. Thus the summits may be classified as climatic refuges. This is especially the case if glacial periods were associated with much drier conditions on oceanic islands as is the case on continents.

The upper limits of vegetation on Mauna Loa, Hawaii: a 50th-anniversary reassessment

In January 1958, a survey of alpine flora was conducted along a recently constructed access road across the upper volcanic slopes of Mauna Loa, Hawaii (2525-3397 m). Only five native Hawaiian species were encountered on sparsely vegetated historic and prehistoric lava flows adjacent to the roadway. A resurvey of roadside flora in 2008 yielded a more than fourfold increase to 22 species, including nine native species not previously recorded. Eight new alien species have now invaded this alpine environment, although exclusively limited to a few individuals in ruderal habitat along the roadway. Alternative explanations for species invasion and altitudinal change over the past 50 years are evaluated: (1) changes related to continuing primary succession on ameliorating (weathering) young lava substrates; (2) local climate change; and (3) road improvements and increased vehicular access which promote enhanced car-borne dispersal of alien species derived from the expanding pool of potential colonizers naturalized on the island in recent decades. Unlike alpine environments in temperate latitudes, the energy component (warming) in climate change on Mauna Loa does not appear to be the unequivocal driver of plant invasion and range extension. Warming may be offset by other climate change factors including rainfall and evapotranspiration.

Prioritizing conservation of tropical dry forests in the Pacific

To identify forests of high priority for conservation in tropical dry forests of New Caledonia, Fiji, the Marquesas and Hawaii, we examined patterns of woody plant species richness (total, native and endemic) and threatened species (IUCN categorization and density) at the stand level, using Gentrys transect method. There were associations between total, native and endemic plant species richness in all four Pacific dry forest regions but we found no significant association with the presence or density of species listed on the IUCN Red List. Dry forests in New Caledonia and Hawaii merit the highest conservation priority in the Pacific, based on level of endemism and number of threatened species. The study sites that merit high conservation priority are Metzdorf, Nekoro and Pindai, in New Caledonia, Kokee and Kaupulehu, in Hawaii, and Vatia, in Fiji. New Caledonia and Fiji have a small dry forest extent and protected area extent compared with other dry forests in biodiversity hotspots. Although we identified priority areas for dry forest conservation, more comparative plot data, presence/absence data in fragments and regional geographical data are needed to adequately manage and protect dry forests in the Pacific.