Mechanisms of plant–plant interactions: concealment from herbivores is more important than abiotic-stress mediation in an African savannah

Louthan, Allison M.; Doak, Daniel F.; Goheen, Jacob R.; Palmer, Todd M.; Pringle, Robert M.

doi:10.1098/rspb.2013.2647

Cited by 41 publications

(51 citation statements)

References 37 publications

(73 reference statements)

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“…These results agree with a previous study at MRC (Coverdale et al 2016), which found that overstory neighbors reduce herbivory, presumably through physical inhibition of browsing mammals; decreased apparency conferred by understory neighbors did not significantly reduce browsing damage (Louthan et al 2014). These results agree with a previous study at MRC (Coverdale et al 2016), which found that overstory neighbors reduce herbivory, presumably through physical inhibition of browsing mammals; decreased apparency conferred by understory neighbors did not significantly reduce browsing damage (Louthan et al 2014).…”

Section: Discussionsupporting

confidence: 91%

“…Associational refuges are commonly assumed to enhance fitness (Agrawal 1998, Louthan et al 2014), but may be deleterious if resource competition between neighbors outweighs the benefits of reduced herbivory (Hay 1986, Barbosa et al 2009). Though it is difficult to accurately measure true lifetime fitness for long-lived perennial plants such as B. trispinosa in natural populations (Campbell 2000), comparisons of key vital rates across habitats can provide useful insights into the relative impacts of herbivory on plant fitness .…”

Section: How Does Association Affect Plant Fitness?mentioning

confidence: 99%

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Good neighbors make good defenses: associational refuges reduce defense investment in African savanna plants

Coverdale

Goheen²,

Palmer

et al. 2018

Ecology

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Intraspecific variation in plant defense phenotype is common and has wide-ranging ecological consequences. Yet prevailing theories of plant defense allocation, which primarily account for interspecific differences in defense phenotype, often fail to predict intraspecific patterns. Furthermore, although individual variation in defense phenotype is often attributed to ecological interactions, few general mechanisms have been proposed to explain the ubiquity of variable defense phenotype within species. Here, we show experimentally that associational refuges and induced resistance interact to create predictable intraspecific variation in defense phenotype in African savanna plants. Physically defended species from four families (Acanthaceae, Asparagaceae, Cactaceae, and Solanaceae) growing in close association with spinescent Acacia trees had 39-78% fewer spines and thorns than did isolated conspecifics. For a subset of these species, we used a series of manipulative experiments to show that this variability is maintained primarily by a reduction in induced responses among individuals that seldom experience mammalian herbivory, whether due to association with Acacia trees or to experimental herbivore exclusion. Unassociated plants incurred 4- to 16-fold more browsing damage than did associated individuals and increased spine density by 16-38% within one month following simulated browsing. In contrast, experimental clipping induced no net change in spine density among plants growing beneath Acacia canopies or inside long-term herbivore exclosures. Associated and unassociated individuals produced similar numbers of flowers and seeds, but seedling recruitment and survival were vastly greater in refuge habitats, suggesting a net fitness benefit of association. We conclude that plant-plant associations consistently decrease defense investment in this system by reducing both the frequency of herbivory and the intensity of induced responses, and that inducible responses enable plants to capitalize on such associations in heterogeneous environments. Given the prevalence of associational and induced defenses in plant communities worldwide, our results suggest a potentially general mechanism by which biotic interactions might predictably shape intraspecific variation in plant defense phenotype.

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Section: Discussionsupporting

confidence: 91%

Section: How Does Association Affect Plant Fitness?mentioning

confidence: 99%

Good neighbors make good defenses: associational refuges reduce defense investment in African savanna plants

Coverdale

Goheen²,

Palmer

et al. 2018

Ecology

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“…; Louthan et al . ). Likewise, contraction and reduced connectivity of understorey patches in the dry season reduces protection from predators, which might reduce individuals’ willingness to venture farther across the landscape.…”

Section: Discussionmentioning

confidence: 97%

Climatic variation modulates the indirect effects of large herbivores on small‐mammal habitat use

Long

Wambua

Goheen

et al. 2017

Journal of Animal Ecology

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Large mammalian herbivores (LMH) strongly shape the composition and architecture of plant communities. A growing literature shows that negative direct effects of LMH on vegetation frequently propagate to suppress the abundance of smaller consumers. Indirect effects of LMH on the behaviour of these consumers, however, have received comparatively little attention despite their potential ecological significance. We sought to understand (i) how LMH indirectly shape small-mammal habitat use by altering the density and distribution of understorey plants; (ii) how these effects vary with climatic context (here, seasonality in rainfall); and (iii) the extent to which behavioural responses of small mammals are contingent upon small-mammal density. We tested the effects of a diverse LMH community on small-mammal habitat use using 4 years of spatially explicit small-mammal trapping and vegetation data from the UHURU Experiment, a replicated set of LMH exclosures in semi-arid Kenyan savanna. Small-mammal habitat use was positively associated with tree density and negatively associated with bare (unvegetated) patches in all plots and seasons. In the presence of LMH, and especially during the dry season, small mammals consistently selected tree cover and avoided bare patches. In contrast, when LMH were excluded, small mammals were weakly associated with tree cover and did not avoid bare patches as strongly. These behavioural responses of small mammals were largely unaffected by changes in small-mammal density associated with LMH exclusion. Our results show that LMH indirectly affect small-mammal behaviour, and that these effects are influenced by climate and can arise via density-independent mechanisms. This raises the possibility that anthropogenic LMH declines might interact with changing patterns of rainfall to alter small-mammal distribution and behaviour, independent of numerical responses by small mammals to these perturbations. For example, increased rainfall in East Africa (as predicted in many recent climate-model simulations) may relax constraints on small-mammal distribution where LMH are rare or absent, whereas increased aridity and/or drought frequency may tighten them.

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“…; Adler, Dalgleish & Ellner and Louthan et al . ;. The number of potentially important drivers will frequently be large in relation to the number of data points (i.e.…”

Section: Under‐explored Drivers and Relative Impacts Of Multiple Driversmentioning

confidence: 99%

Advancing environmentally explicit structured population models of plants

et al. 2016

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Summary The relationship between the performance of individuals and the surrounding environment is fundamental in ecology and evolutionary biology. Assessing how abiotic and biotic environmental factors influence demographic processes is necessary to understand and predict population dynamics, as well as species distributions and abundances. We searched the literature for studies that have linked abiotic and biotic environmental factors to vital rates and, using structured demographic models, population growth rates of plants. We found 136 studies that had examined the environmental drivers of plant demography. The number of studies has been increasing rapidly in recent years. Based on the reviewed studies, we identify and discuss several major gaps in our knowledge of environmentally driven demography of plants. We argue that some drivers may have been underexplored and that the full potential of spatially and temporally replicated studies may not have been realized. We also stress the need to employ relevant statistical methods and experiments to correctly identify drivers. Moreover, assessments of the relationship between drivers and vital rates need to consider interactive, nonlinear and indirect effects, as well as effects of intraspecific density dependence. Synthesis. Much progress has already been made by using structured population models to link the performance of individuals to the surrounding environment. However, by improving the design and analyses of future studies, we can substantially increase our ability to predict changes in plant population dynamics, abundances and distributions in response to changes in specific environmental drivers. Future environmentally explicit demographic models should also address how genetic changes prompted by selection imposed by environmental changes will alter population trajectories in the face of continued environmental change and investigate the reciprocal feedback between plants and their biotic drivers.

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Mechanisms of plant–plant interactions: concealment from herbivores is more important than abiotic-stress mediation in an African savannah

Cited by 41 publications

References 37 publications

Good neighbors make good defenses: associational refuges reduce defense investment in African savanna plants

Good neighbors make good defenses: associational refuges reduce defense investment in African savanna plants

Climatic variation modulates the indirect effects of large herbivores on small‐mammal habitat use

Advancing environmentally explicit structured population models of plants

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