Biology subjects

Fordham, D. A.

Publications and source records attributed to Fordham, D. A..

3 recordsLinked to original sources

bioRxiv2023

Reconstructing colonization dynamics to establish how human activities transformed island biodiversity

AimThe drivers and dynamics of initial human migrations across individual islands and archipelagos are poorly understood, affecting assessments of human-modification of island biodiversity. Here, we describe and test a process-explicit approach for reconstructing human arrival and expansion on islands, which combines archaeological and climate records with high-resolution spatial population models. Using Polynesian colonisation of New Zealand as an example, we show that our new method can generate information crucial for assessing how humans affected biodiversity on islands. InnovationThe transition of islands from prehuman to human dominated ecosystems has typically been assessed by comparing biodiversity before and after time of first arrival, without considering the potential importance of the spatiotemporal dynamics of the human expansion event. Our new approach, which uses pattern-oriented modelling methods to combine inferences of human colonisation dynamics from dated archaeological material with spatially explicit population models, produces validated reconstructions of the pattern and pace of human migration across islands at high spatiotemporal resolutions. From these reconstructions, demographic and environmental drivers of human colonization can be identified, and the role that people had on biodiversity established. Using this technique, we show that closely reconciling inferences of Polynesian colonisation of New Zealand requires there to have been a single founding population of approximately 500 people, arriving between 1233 and 1257 AD, settling multiple areas, and expanding quickly over both North and South islands. The resultant maps of M[a]ori colonisation dynamics provide new opportunities to better determine how human activities transformed biodiversity of New Zealand in space and time. Main conclusionsProcess-explicit models can reconstruct human migration across large islands, producing validated, high resolution spatiotemporal projections of human occupancy and abundance that account for dispersal and population dynamics. This modelling framework should prove effective across any islands and archipelagos where climate and archaeological records are available.

ecology↗

bioRxiv2022

Impact of Holocene environmental change on the evolutionary ecology of an Arctic top predator

The Arctic is among the most climatically sensitive environments on Earth, and the disappearance of multiyear sea-ice in the Arctic Ocean is predicted within decades. As apex predators, polar bears are sentinel species for addressing the impact of environmental variability on Arctic marine ecosystems. By integrating genomics, isotopic analysis, morphometrics, and ecological modelling, we investigate how Holocene environmental changes affected the evolutionary ecology of polar bears around Greenland. We show that throughout the last [~]11,000 years, Greenlandic polar bears have been heavily influenced by changes in sea-surface temperature (SST) and sea-ice cover. Most notable are major reductions in effective population size at the beginning of the Holocene and during the Holocene Thermal Maximum [~]6 kya, which coincide with increases in annual mean SST, reduction in sea-ice covers, declines in suitable habitat, and shifts in suitable habitat northwards. Furthermore, we show how individuals sampled from west and east Greenland are genetically, morphologically, and ecologically distinct. We find bears sampled in west Greenland to be larger, more genetically diverse and have diets dominated by ringed seals, whereas bears from east Greenland are smaller and less diverse with more varied diets, putatively driven by regional biotic differences. Taken together, we provide novel insights into the vulnerability of polar bears to environmental change, and how the Arctic marine ecosystem plays a vital role in shaping the evolutionary and ecological trajectories of its inhabitants. TeaserMultivariate investigations of the environments role in the evolutionary ecology of Greenlandic polar bears.

evolutionary biology↗

bioRxiv2021

Humans hastened the range collapse and extinction of woolly mammoth

Pathways to extinction start long before the death of the last individual. However, causes of early-stage population declines and the susceptibility of small residual populations to extirpation are typically studied in isolation. Using validated process-explicit models, we disentangle the ecological mechanisms and threats that were integral in the initial decline and later extinction of the woolly mammoth. We show that reconciling ancient DNA data on woolly mammoth population decline with fossil evidence of location and timing of extinction requires process-explicit models with specific demographic and niche constraints, and a constrained synergy of climatic change and human impacts. Validated models needed humans to hasten climate-driven population declines by many millennia, and to allow woolly mammoths to persist in mainland Arctic refugia until the mid-Holocene. Our results show that the role of humans in the extinction dynamics of woolly mammoth began well before the Holocene, exerting lasting effects on the spatial pattern and timing of its range-wide extinction.

ecology↗