scholarly journals Direct and indirect effects of episodic frost on plant growth and reproduction in subalpine wildflowers

2017 ◽  
Vol 24 (2) ◽  
pp. 848-857 ◽  
Author(s):  
Gabriella L. Pardee ◽  
David W. Inouye ◽  
Rebecca E. Irwin
Keyword(s):  
Plant Growth ◽  
Indirect Effects ◽  
Direct And Indirect Effects ◽  
Growth And Reproduction

scholarly journals Counteracting gradients of light and soil nutrients in the understorey of Mediterranean oak forests

Web Ecology ◽  
2006 ◽  
Vol 6 (1) ◽  
pp. 67-74 ◽  
Author(s):  
L. V. García ◽  
S. Maltez-Mouro ◽  
I. M. Pérez-Ramos ◽  
H. Freitas ◽  
T. Marañón
Keyword(s):  
Plant Growth ◽  
Soil Nutrients ◽  
Indirect Effects ◽  
Light Availability ◽  
Oak Forests ◽  
P Availability ◽  
Direct And Indirect Effects ◽  
Canopy Density ◽  
Litter Accumulation ◽  
Understorey Plant

Abstract. The forest canopy modifies the availability of resources (light, water, and soil nutrients) in the understorey. In this paper we analyze the relationships between woody canopy density, litter accumulation, and topsoil N and P availability in the understorey of two oak forests: one in southern Portugal and the other in southern Spain. Both forests persist on low-nutrient soils, particularly poor in P. We hypothesize that direct and indirect effects of the canopy overstorey cause opposite gradients in the availability of essential resources (light and key soil nutrients) in the understorey. In both studied forests we found significant relationships between the overall canopy density, light availability, topsoil litter accumulation, and the availability of N and P, which frequently limit plant growth. Path analysis (by Shipley’s d-sep method) showed that the available data were consistent with the proposed causal model. The average values of soil variables at the end quartiles of the light-availability gradient were compared. Results showed large differences in litter accumulation (~30×) and available-N and -P topsoil concentrations (~3×) in the Spanish forest (with the wider environmental gradient). Furthermore, P increased from the “very low” range to the “low” or even the “optimum” range of availability (according to standard plant growth criteria), which suggests potential effects on the growth of the understorey plant species. We conclude that the counteracting gradients of the essential resources – light and nutrients – in the forest understorey resulted from direct and indirect effects of the canopy overstorey, respectively. We suggest that these counteracting effects of the woody canopy on essential resources of different nature must be considered when interpreting the patterns of understorey plant populations and communities.

Azteca instabilis ants and the defence of a coffee shade tree: an ant–plant association without mutual rewards in Chiapas, Mexico

2010 ◽  
Vol 26 (3) ◽  
pp. 343-346 ◽  
Author(s):  
David J. Gonthier ◽  
Gabriella L. Pardee ◽  
Stacy M. Philpott
Keyword(s):  
Plant Growth ◽  
Indirect Effect ◽  
Indirect Effects ◽  
Herbivorous Insects ◽  
Plant Association ◽  
Plant Interactions ◽  
Mutualistic Interaction ◽  
Nesting Sites ◽  
Floral Nectaries ◽  
Growth And Reproduction

Ants (Hymenoptera: Formicidae) are important predators of herbivorous insects on plants (Rosumek et al. 2009). Ant removal or absence may result in negative indirect effects on plants, as herbivore abundance and herbivory increase and plant growth and reproduction decline (Rosumek et al. 2009, Schmitz et al. 2000). Ant presence on plants often results from a mutualistic interaction. For example, strong highly coevolved ant–plant mutualisms are found on myrmecophytic plants that house ants in domatia (specialized nesting sites). Weaker mutualistic associations are found with myrmecophilic plants that only offer extra-floral nectaries (EFNs) or food bodies to attract ants, or on other plants hosting honeydew-producing hemipterans (indirect ant–plant interactions) that mediate ant abundance (Hölldobler & Wilson 1990). However, in most cases, plants and arboreal ants form more passive associations, where ants nest in the natural cavities of branches or bark, or construct carton nests on plant substrates (Hölldobler & Wilson 1990) and the only reward plants offer these ants is the use of their substrates. In these situations the indirect effect of ants on plants is merely by chance, a byproduct of ant presence (byproduct association).

Direct and indirect effects of dynamic social impact

2005 ◽  
Author(s):  
Dana M. Binder ◽  
Martin J. Bourgeois ◽  
Christine M. Shea Adams
Keyword(s):  
Indirect Effects ◽  
Social Impact ◽  
Direct And Indirect Effects
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