Short- and long-term responses of riparian cottonwoods (Populus spp.) to flow diversion: Analysis of tree-ring radial growth and stable carbon isotopes.

Long duration tree-ring records with annual precision allow for the reconstruction of past growing conditions. Investigations limited to the most common tree-ring proxy of ring width can be difficult to interpret, however, because radial growth is affected by multiple environmental processes. Furthermore, studies of living trees may miss important effects of drought on tree survival and forest changes.

Supplementary testosterone inhibits paternal care in a tropically breeding sparrow, Zonotrichia capensis.

In most male birds that exhibit paternal care, elevation in testosterone above the breeding baseline reduces nestling provisioning, which can be detrimental to offspring survival. Mechanisms that may allow some males to avoid this detrimental effect of elevated testosterone include (1) decreased sensitivity to testosterone's effects on behavior and (2) uncoupling of testosterone secretion from territorial challenges (thus reducing the number of transient elevations in testosterone above the breeding baseline). Both of these "cost-avoidance" mechanisms have been documented, but whether selection for these mechanisms is correlated or independent is unknown.