Search

Changes in climate can alter environmental conditions faster than most species can adapt. A prediction under a warming climate is that species will shift their distributions poleward through time. While many studies focus on range shifts, latitudinal shifts in species' optima can occur without detectable changes in their range. We quantified shifts in latitudinal optima for 209 North American bird species over the last 55 y. The latitudinal optimum (m) for each species in each year was estimated using a bespoke flexible non-linear zero-inflated model of abundance vs. latitude, and the annual shift in m through time was quantified. One-third (70) of the bird species showed a significant shift in their optimum. Overall, mean peak abundances of North American birds have shifted northward, on average, at a rate of 1.5 km per year (±0.58 SE), corresponding to a total distance moved of 82.5 km (±31.9 SE) over the last 55 y. Stronger poleward shifts at the continental scale were linked to key species' traits, including thermal optimum, habitat specialization, and territoriality. Shifts in the western region were larger and less variable than in the eastern region, and they were linked to species' thermal optimum, habitat density preference, and habitat specialization. Individual species' latitudinal shifts were most strongly linked to their estimated thermal optimum, clearly indicating a climate-driven response. Displacement of species from their historically optimal realized niches can have dramatic ecological consequences. Effective conservation must consider within-range abundance shifts. Areas currently deemed "optimal" are unlikely to remain so. [ABSTRACT FROM AUTHOR]

Interactions between pairs of binary stars play an important role in the dynamics of dense stellar systems. One possible outcome of a binary–binary encounter is full ionization: the destruction of both interacting binaries resulting in four separating single stars. This process is only possible for positive total energy, and the cross-section for full ionization falls to zero at zero total energy. In the context of a stellar system, full ionization is most likely to involve the interaction of two soft binaries with low binding energies. We consider the case where the four stars have a similar mass and derive an asymptotic power law relating the cross-section for full ionization with the total energy when this latter quantity is small. Our new theory makes use of the fact that the most dramatic changes in scale and energies of a few-body system occur when its components pass near to a central configuration. Numerical simulations are used to verify the result. [ABSTRACT FROM AUTHOR]