Multiple Life-history Stages Research Articles

Facilitation in multiple life-history stages: evidence for nucleated succession in coastal dunes

Understanding plant interactions during succession is a central goal of plant ecology. The nucleation model of succession proposes that facilitative interactions lead to outward radiations of colonization from established plants. I tested the nucleation hypothesis for early successional plants on the primary dunes of barrier islands in the southeastern United States. On the coast of Florida and Georgia, I sampled the above-ground vegetation and the seed bank, and conducted a seedling emergence experiment in the field. Vegetation sampling at both field sites showed more positive correlations in percent cover of adult species than expected by chance. At both sites, there were significantly more seeds under plants than in open microsites. Seeds of the same species as the adult plants in the vegetated microsites were removed from the analysis, so the accumulation of seeds under adults is not due simply to a seed shadow effect. Seeds of six species were added to plots under plants and in open microsites, and seedling emergence was significantly higher under plants than in the open. The findings support the predictions of the nucleation hypothesis for the early life-history stages of seed dispersal and germination, and help to explain the clumped distribution of dune plants seen in the field. The results add further support for the contention that facilitation is an important mode of plant interaction in stressful and disturbed habitats.

Evolution of Egg Size in Free-Spawners: Consequences of the Fertilization-Fecundity Trade-Off

Evolution of Egg Size in Free-Spawners: Consequences of the Fertilization-Fecundity Trade-Off

GnRH-Like Immunoreactivity in the Peripheral Olfactory System and Forebrain of Atlantic Salmon <i>(Salmo salar): </i>A Reassessment at Multiple Life History Stages

Neurons with gonadotropin releasing hormone-like immunoreactivity (GnRH-ir) were identified within the peripheral olfactory system of Atlantic salmon (Salmo salar) at multiple life history stages. Within the forebrain, GnRH-ir somata were found in the preoptic area and in the caudomedial olfactory bulb in a position comparable to the ganglion of the nervus terminalis of other teleosts. Somata positive for GnRH were also found throughout the rostro-caudal extent of the olfactory nerve, and clustered within the medial component of the olfactory nerve as it arises from the olfactory epithelium. Results from tract tracing experiments with horseradish peroxidase indicate that at least some cells in this cluster project to the retina, suggesting that they too are part of a terminal nerve ganglion as anatomically defined in other vertebrates. We suggest that the presence of a distinct cluster of terminal nerve ganglion cells in the immediate vicinity of the olfactory epithelium may point to a peripheral site of neuromodulatory control in the olfactory system in salmon and perhaps in other teleosts as well.