Human activities can affect the behaviour of mammals through the modification of habitats, changes in predation pressure or alterations in food distribution and availability. We analysed the association and ranging patterns of 242 individually identified bottlenose dolphins (Tursiops aduncus) in eastern Moreton Bay, Queensland, Australia, and distinguished two separate communities of dolphins. Unlike bottlenose dolphins elsewhere, the communities' core areas overlapped substantially. There was a correlation between the dolphins' responses to fishing activities and community membership-members of one community feed in association with trawlers and members of the other do not. Apart from feeding mode, the communities differed in habitat preference and group sizes. Inadvertent anthropogenic impacts on animals' societies are likely to be far more widespread than just this study and can increase conservation challenges. In this instance, managers need to consider the two communities' differing habitat requirements and their behavioural traditions in conservation planning.

Extinctions can dramatically reshape biological communities. As a case in point, ancient mass extinction events apparently facilitated dramatic new evolutionary radiations of surviving lineages. However, scientists have yet to fully understand the consequences of more recent biological upheaval, such as the megafaunal extinctions that occurred globally over the past 50 kyr. New Zealand was the world's last large landmass to be colonized by humans, and its exceptional archaeological record documents a vast number of vertebrate extinctions in the immediate aftermath of Polynesian arrival approximately AD 1280. This recently colonized archipelago thus presents an outstanding opportunity to test for rapid biological responses to extinction. Here, we use ancient DNA (aDNA) analysis to show that extinction of an endemic sea lion lineage (Phocarctosspp.) apparently facilitated a subsequent northward range expansion of a previously subantarctic-limited lineage. This finding parallels a similar extinction–replacement event in penguins (Megadyptesspp.). In both cases, an endemic mainland clade was completely eliminated soon after human arrival, and then replaced by a genetically divergent clade from the remote subantarctic region, all within the space of a few centuries. These data suggest that ecological and demographic processes can play a role in constraining lineage distributions, even for highly dispersive species, and highlight the potential for dynamic biological responses to extinction.