Herbivory can hinder restoration success by limiting the recovery of plant biodiversity. This study investigates whether plant-plant interactions, such as associational defenses, can increase the ...survival of a palatable species in restoration contexts where herbivory inhibits recovery. Specifically, we investigate the potential of associational defenses by the perennial
Nuphar advena
(yellow pond-lily) to influence the growth and survival of
Zizania aquatica
(annual wild rice) in a freshwater tidal marsh restoration where goose herbivory has limited
Z. aquatica
recovery. Wild rice was planted within exclosures and unfenced control plots located within patches of
N. advena
or adjacent mudflat. In an additional treatment to test the negative effects of light competition, we planted
Z. aquatica
in exclosures located within experimental clearings in
N. advena
patches. We also surveyed grazing pressure on naturally-occurring
Z. aquatica
within transects that spanned
N. advena
patches and adjacent mudflat. Based on observational and experimental results,
N. advena
provided clear protection from grazing for
Z. aquatica
. However, there was a cost to
Z. aquatica
growing in
N. advena
patches– plantings within
N. advena
had greater mortality and significantly reduced biomass due to low light availability.
The woody plant communities found on residential properties constitute an integral component of cities’ green infrastructure and serve as a nexus between urban residents and the natural world. ...Despite this importance, residential landscapes are infrequently designed with principles of sustainability in mind, resulting in the extensive use of pesticides to suppress a diverse array of plant pests. In this study, we ask whether ecological theory can inform the sustainable design and management of woody plant communities on urban residential properties. The associational resistance and dilution effect hypotheses are analogous hypotheses, which posit that increasing biodiversity can inhibit the abundance of herbivores and pathogens, respectively. Importantly, theory suggests that it might not just be diversity that matters, but the right kind of diversity (i.e., community composition). Previous studies have demonstrated that herbivore abundance can be greater on native plants compared to exotic plants in residential landscapes. However, little is known regarding whether this translates into greater numbers of interventions to reduce damage associated with plant pests on native plants. To test these hypotheses, we utilized a multi-year, commercial plant health care program dataset. We examined, at the residential property scale, the relationships between woody plant diversity, the percentage of plants that were native, and pest management interventions. We found that the number of pest management interventions targeting phytophagous arthropods, but not plant pathogens, was negatively related to woody plant biodiversity. The percentage of native plants on a property had no relationship with the number of pest management interventions that occurred. Consequently, efforts to increase woody plant biodiversity in residential landscapes could result in increased phytophagous arthropod pest suppression, thereby reducing the need for pesticide applications and their associated adverse effects.
Aims
The stress gradient hypothesis predicts that competition will be important in productive environments while facilitation will be common in environments with high stress or consumer pressure. ...However, abiotic stress and grazing may vary independently and even occur simultaneously. Here we examine the outcome of plant interactions in grazed wetlands where consumer pressure and abiotic stress occur concurrently. We hypothesized that cattle grazing and microhabitat would alter the outcome of plant interactions. Given that wetland edges are drier and less productive than wetland centers we expected that facilitation would be greatest in drier wetland edges due to greater abiotic stress regardless of cattle presence.
Location
Archbold Biological Station's Buck Island Ranch (BIR), south‐central Florida, USA (27°09′ N, 81°11′ W).
Methods
We conducted an experiment for two growing seasons in ten wetlands, five exposed to cattle grazing and five fenced. Two wetland obligate plants were included (Panicum hemitomon and Alternanthera philoxeroides), and plots were assigned to three treatments (a) all neighbors removed; (b) all neighbors removed except Juncus effusus, a dominant, unpalatable plant; and (c) all neighbors intact (control), in both wetland centers and edges. Differences in survival, change in height and number of leaves were assessed.
Results
In ungrazed wetlands, plant survival was higher in wetland edges vs centers, while it did not differ between microhabitats in grazed wetlands. Survival in wetland edges was further increased by the presence of Juncus effusus. Positive interactions under grazed conditions were clear when plant height was assessed, but negative interactions affected leaf production in both ungrazed and grazed wetlands.
Conclusions
Grazing interacts with wetland microhabitat to alter plant survival. Facilitative interactions on plant height were apparent in grazed wetlands. Understanding how plant interactions change under different biotic and abiotic contexts is important for informing ecosystem restoration and management.
We examined plant interactions in grazed wetlands where consumer pressure and abiotic stress occur concurrently. Grazing and microhabitat interacted to impact plant survival. Competition decreased survival in ungrazed wet microhabitats while plant survival was similar in dry and wet microhabitats in grazed wetlands. Assessing multiple effects on plant interactions is important for understanding plant community change and management.
Plant-emitted semi-volatile compounds have low vaporization rates at 20-25°C and may therefore persist on surfaces such as plant foliage. The passive adsorption of arthropod-repellent semi-volatiles ...to neighbouring foliage could convey associational resistance, whereby a plant's neighbours reduce damage caused by herbivores. We found that birch (Betula spp.) leaves adsorb and re-release the specific arthropod-repelling C₁₅ semi-volatiles ledene, ledol and palustrol produced by Rhododendron tomentosum when grown in mixed association in a field setup. In a natural habitat, a higher concentration of ledene was released from birches neighbouring R. tomentosum than from birches situated > 5 m from R. tomentosum. Emission of α-humulene, a sesquiterpene synthesized by both Betula pendula and R. tomentosum, was also increased in R. tomentosum-neighbouring B. pendula. In assessments for associational resistance, we found that the polyphagous green leaf weevils (Polydrusus flavipes) and autumnal moth (Epirrita autumnata) larvae both preferred B. pendula to R. tomentosum. P. flavipes also preferred birch leaves not exposed to R. tomentosum to leaves from mixed associations. In the field, a reduction in Euceraphis betulae aphid density occurred in mixed associations. Our results suggest that plant/tree species may be protected by semi-volatile compounds emitted by a more herbivore-resistant heterospecific neighbour.
An individual's susceptibility to attack can be influenced by conspecific and heterospecifics neighbors. Predicting how these neighborhood effects contribute to population-level processes such as ...competition and evolution requires an understanding of how the strength of neighborhood effects is modified by changes in the abundances of both consumers and neighboring resource species. We show for the first time that consumer density can interact with the density and frequency of neighboring organisms to determine the magnitude of neighborhood effects. We used the bean beetle, Callosobruchus maculatus, and two of its host beans, Vigna unguiculata and V radiata, to perform a response-surface experiment with a range of resource densities and three consumer densities. At low beetle density, damage to beans was reduced with increasing conspecific density (i.e., resource dilution) and damage to the less preferred host, V. unguiculata, was reduced with increasing V radiata frequency (i.e., frequency-dependent associational resistance). As beetle density increased, however, neighborhood effects were reduced; at the highest beetle densities neither focal nor neighboring resource density nor frequency influenced damage. These findings illustrate the importance of consumer density in mediating indirect effects among resources, and suggest that accounting for consumer density may improve our ability to predict population-level outcomes of neighborhood effects and our use of them in applications such as mixed-crop pest management.
Why can hosts coexist with conspecifics or phylogenetically proximate neighbours despite sharing specialist enemies? Do the hosts evolve increased enemy resistance? If so, does this have costs in ...terms of climatic‐stress resistance, or in such neighbourhoods, does climatic‐stress select for resistances that are multifunctional against climate and enemies? We studied oak (Quercus petraea) descendants from provenances of contrasting phylogenetic neighbourhoods and climates in a 25‐year‐old common garden. We found that descendants from conspecific or phylogenetically proximate neighbourhoods had the toughest leaves and fewest leaf miners, but no reduction in climatic‐stress resistance. Descendants from such neighbourhoods under cold or dry climates had the highest flavonol and anthocyanin levels and the thickest leaves. Overall, populations facing phylogenetically proximate neighbours can rapidly evolve herbivore resistance, without cost to climatic‐stress resistance, but possibly facilitating resistance against cold and drought via multifunctional traits. Microevolution might hence facilitate ecological coexistence of close relatives and thereby macroevolutionary conservatism of niches.
Plants can alter nutritional availability, structure, and chemistry of the soil they grow in. These soil changes can positively or negatively influence the growth and metabolism of other plants that ...co-occur or grow later in the conditioned soil. Plant-soil feedbacks could affect community interactions and dynamics but also be applied in sustainable agriculture to promote plant growth and resistance to pests. In this study, we use a maize companion cropping system, commonly known as “push-pull,” as a model to investigate soil-mediated effects of functional biodiversity, on maize plant growth, and resistance against insect herbivores. We grew maize in soils collected from push-pull (polyculture) and non-push-pull (monoculture) fields. We evaluated maize performance by measuring plant growth, as well as resistance traits (herbivore oviposition and larval feeding, production of defense-related volatile, and non-volatile secondary defense metabolites). Maize plants grown in soil conditioned by push-pull companion cropping had a higher growth rate compared to those grown in soil from non-push-pull monoculture fields. In addition, soil from push-pull fields induced a constitutively higher and qualitatively different emission of volatile organic compounds than soil from non-push-pull fields. Moreover, secondary defense metabolites such as 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), were produced in larger quantities in plants grown in soil from push-pull fields compared to those from monoculture fields. These soil-mediated alterations in plant secondary metabolism were associated with reduced herbivory by larvae of the stemboring pest Chilo partelllus. This study provides novel evidence that plant-soil feedbacks can affect plant metabolism, growth, and resistance to pests. The observed soil-mediated effects on maize plant secondary metabolism can be viewed as emergent properties of plant community composition as well as a potent mechanism of associational resistance. In addition, these soil-conditioning effects provide a novel pest control mechanism of push-pull companion cropping.
The nurse-protégé interaction involves benefits for the protected species by the reduction in the abiotic stress intensity. Nurse plants, however, could affect other biotic interactions by reducing ...that natural benefit. Studies about plant-plant-animal interaction assume that plants can recover from and/or avoid granivory when they grow under higher resources availability; nevertheless, in early stages they could be subject to different pressures. Thus, the resistance or susceptibility to granivores could occur because of differential responses of the plants (nurse and protected) to the environment (abiotic factors) or as results of differential responses of the plants to granivores (biotic factors), altering the probability of the resistance or susceptibility of plants to herbivores. We evaluated diurnal and nocturnal granivore activity on P. leucocephalus seeds, and we also evaluated if a nurse species could determine the association type (i.e. associational resistance or susceptibility) from the intensity of the granivore in early stage (e.g. seeds) of the P. leucocephalus life cycle. We found higher granivory under nurse plants than in open spaces (the control group), indicating associational susceptibility. Furthermore, most of the granivory was performed by nocturnal animals (mice). These results suggest a cost/benefit of the nurse-protégé interaction, which can be modulated by the granivory.
•The nurse-protégé interaction involves benefits for the protected species.•We evaluated diurnal and nocturnal granivory on Pilosocereus leucocephalus.•We found higher granivory under nurse plants than in open spaces.•Most of the granivory was performed by nocturnal animals.•Our results suggest a cost/benefit of the nurse-protégé interaction.
Dinoflagellates are a major cause of harmful algal blooms (HABs), with consequences for coastal marine ecosystem functioning and services. Alexandrium fundyense (previously Alexandrium tamarense) is ...one of the most abundant and widespread toxigenic species in the temperate Northern and Southern Hemisphere and produces paralytic shellfish poisoning toxins as well as lytic allelochemical substances. These bioactive compounds may support the success of A. fundyense and its ability to form blooms. Here we investigate the impact of grazing on monoclonal and mixed set-ups of highly (Alex2) and moderately (Alex4) allelochemically active A. fundyense strains and a non-allelochemically active conspecific (Alex5) by the heterotrophic dinoflagellate Polykrikos kofoidii. While Alex4 and particularly Alex5 were strongly grazed by P. kofoidii when offered alone, both strains grew well in the mixed assemblages (Alex4 + Alex5 and Alex2 + Alex5). Hence, the allelochemical active strains facilitated growth of the non-active strain by protecting the population as a whole against grazing. Based on our results, we argue that facilitation among clonal lineages within a species may partly explain the high genotypic and phenotypic diversity of Alexandrium populations. Populations of Alexandrium may comprise multiple cooperative traits that act in concert with intraspecific facilitation, and hence promote the success of this notorious HAB species.
Mixedwood stands are composed of hardwoods and softwoods, with neither comprising greater than 75%–80% of basal area or aboveground biomass. By conferring associational resistance and greater ...resilience to forests when stressed or disturbed, the more diverse composition of mixedwood stands contributes to forest health. We analyzed three examples where mixedwood stands are more resistant to insect infestations in eastern North America. In balsam fir (Abies balsamea L. Mill.) and spruce (Picea spp.) forests, susceptibility and vulnerability to spruce budworm infestations is reduced with increasing hardwood density. In mid-Atlantic oak-dominated forests, oak mortality following gypsy moth infestations was much greater in oak-dominated forests than in oak–pine mixedwoods, while pine mortality during southern pine beetle infestations was greater in pine-dominated forests than in oak–pine mixedwoods. Overall, mixedwood stands have greater resistance to infestations of defoliators and bark beetles and recover more rapidly from disturbances, reducing economic losses associated with tree mortality and mitigating short-term impacts to ecosystem functioning resulting from insect damage, especially carbon sequestration. Finally, we discuss challenges and opportunities for mixedwood management to minimize insect damage. Management strategies that incorporate mixedwood stands may provide better continuity in supply of forest products and ecosystem services in the face of projected increases in insect infestations associated with changing climate.
PDF
