Herbivore-Specific, Density-Dependent Induction of Plant Volatiles: Honest or “Cry Wolf” Signals?

A continuous time and age model which reflects the effect of older age-groups on mortality in young is presented. The conditions under which this model is unstable and the characteristics of solutions under various conditions are examined. Results obtained are related to results obtained by others from stock–recruitment models. Analytical expressions for the period of oscillations, the effect of fishing all age-classes, and the effect of the slope of the stock–recruitment curve at the replacement point support earlier simulation results. The effect on the model of size-selective fishing is shown to be a decrease in the stability of the population in some cases. These results are demonstrated with a model that approximately reflects the Dungeness crab (Cancer magister) population in northern California. The cyclic behavior of this population is similar to an unstable mode of the model. Conditions under which this mode arises are derived and potential causes of decreased stability, among which is fishing, are examined. Key words: fishery, model, stability, Dungeness crab, age-specific, density-dependent, stock–recruitment, cannibalism, Carcinonemertes

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Urbanization impacts on production and recruitment of Fundulus heteroclitus in salt marsh creeks

Marine Ecology Progress Series ◽

10.3354/meps13378 ◽

2020 ◽

Vol 645 ◽

pp. 187-204

Author(s):

PJ Rudershausen ◽

JA Buckel

Keyword(s):

Salt Marsh ◽

Salt Marshes ◽

Fundulus Heteroclitus ◽

Multiple Factor Analysis ◽

Southeastern Usa ◽

Density Dependent ◽

Dependent Relationship ◽

Juvenile Abundance ◽

The Relationship ◽

Throw Trap

It is unclear how urbanization affects secondary biological production in estuaries in the southeastern USA. We estimated production of larval/juvenile Fundulus heteroclitus in salt marsh areas of North Carolina tidal creeks and tested for factors influencing production. F. heteroclitus were collected with a throw trap in salt marshes of 5 creeks subjected to a range of urbanization intensities. Multiple factor analysis (MFA) was used to reduce dimensionality of habitat and urbanization effects in the creeks and their watersheds. Production was then related to the first 2 dimensions of the MFA, month, and year. Lastly, we determined the relationship between creek-wide larval/juvenile production and abundance from spring and abundance of adults from autumn of the same year. Production in marsh (g m-2 d-1) varied between years and was negatively related to the MFA dimension that indexed salt marsh; higher rates of production were related to creeks with higher percentages of marsh. An asymptotic relationship was found between abundance of adults and creek-wide production of larvae/juveniles and an even stronger density-dependent relationship was found between abundance of adults and creek-wide larval/juvenile abundance. Results demonstrate (1) the ability of F. heteroclitus to maintain production within salt marsh in creeks with a lesser percentage of marsh as long as this habitat is not removed altogether and (2) a density-dependent link between age-0 production/abundance and subsequent adult recruitment. Given the relationship between production and marsh area, natural resource agencies should consider impacts of development on production when permitting construction in the southeastern USA.

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