16 research outputs found
Relationships among fishes and their prey in a nearshore sand community off southern California
The microbial flora from root canals and periodontal pockets of non-vital teeth associated with advanced periodontitis
Control of the annual cycle in birds: endocrine constraints and plasticity in response to ecological variability
This paper reviews information from ecological and physiological studies to assess how extrinsic
factors can modulate intrinsic physiological processes. The annual cycle of birds is made up of a
sequence of life-history stages: breeding, moult and migration. Each stage has evolved to occur at the
optimum time and to last for the whole duration of time available. Some species have predictable
breeding seasons, others are more flexible and some breed opportunistically in response to
unpredictable food availability. Photoperiod is the principal environmental cue used to time each
stage, allowing birds to adapt their physiology in advance of predictable environmental changes.
Physiological (neuroendocrine and endocrine) plasticity allows non-photoperiodic cues to modulate
timing to enable individuals to cope with, and benefit from, short-term environmental variability.
Although the timing and duration of the period of full gonadal maturation is principally controlled by
photoperiod, non-photoperiodic cues, such as temperature, rainfall or food availability, could
potentially modulate the exact time of breeding either by fine-tuning the time of egg-laying within the
period of full gonadal maturity or, more fundamentally, by modulating gonadal maturation and/or
regression. The timing of gonadal regression affects the time of the start of moult, which in turn may
affect the duration of the moult. There are many areas of uncertainty. Future integrated studies are
required to assess the scope for flexibility in life-history strategies as this will have a critical bearing on
whether birds can adapt sufficiently rapidly to anthropogenic environmental changes, in particular
climate change