Effects Of Intraspecific Diversity Research Articles

Cross-domain diversity effects: linking diatom species richness, intraspecific richness, and biomass production to host-associated bacterial diversity.

Interactions between bacteria and microalgae are important for the functioning of aquatic ecosystems, yet interactions based on the biodiversity of these two taxonomic domains have been scarcely studied. Specifically, it is unclear whether a positive biodiversity-productivity relationship in phytoplankton is largely facilitated by niche partitioning among the phytoplankton organisms themselves or whether associated bacterial communities play an additional role in modifying these diversity effects. Moreover, the effects of intraspecific diversity in phytoplankton communities on bacterial community diversity have not been tested. To address these points, we factorially manipulated both species and intraspecific richness of three diatoms to test the effects of diatom species/strain diversity on biomass production and bacterial diversity in algae-bacteria communities. The results show that diatom intraspecific diversity has significant positive effects on culture biomass and the diversity of the associated free-living bacterial community (0.2-3μm size fraction), which are comparable in magnitude to species diversity effects. However, there were little to no effects of diatom diversity on host-associated bacterial diversity (>3μm size fraction), or of bacterial diversity on biomass production. These results suggest a decoupling of bacterial diversity from the diatom diversity-productivity relationship and provide early insights regarding the relations between diversity across domains in aquatic ecosystems.

Who Cares More about Chemical Defenses — the Macroalgal Producer or Its Main Grazer?

The consequences of defensive secondary metabolite concentrations and interspecific metabolite diversity on grazers have been extensively investigated. Grazers which prefer certain food sources are often found in high abundance on their host and as a result, understanding the interaction between the two is important to understand community structure. The effects of intraspecific diversity, however, on the grazer are not well understood. Within a single, localized geographic area, the Antarctic red seaweed Plocamium sp. produces 15 quantitatively and qualitatively distinct mixtures of halogenated monoterpenes ("chemogroups"). Plocamium sp. is strongly chemically defended which makes it unpalatable to most grazers, except for the amphipod Paradexamine fissicauda. We investigated differences in the feeding and growth rates of both Plocamium sp. and P. fissicauda, in addition to grazer reproductive output, in relation to different chemogroups. Some chemogroups significantly reduced the grazer's feeding rate compared to other chemogroups and a non-chemically defended control. The growth rate of Plocamium sp. did not differ between chemogroups and the growth rates of P. fissicauda also did not show clear patterns between the feeding treatments. Reproductive output, however, was significantly reduced for amphipods on a diet of algae possessing one of the chemogroups when compared to a non-chemically defended control. Hence, intraspecific chemodiversity benefits the producer since certain chemogroups are consumed at a slower rate and the grazer's reproductive output is reduced. Nevertheless, the benefits outweigh the costs to the grazer as it can still feed on its host and closely associates with the alga for protection from predation.

Faba Bean Variety Mixture Can Modulate Faba Bean–Wheat Intercrop Performance Under Water Limitation

Commercial legume varieties vary in terms of their drought tolerance when grown as sole crops, though relatively little is known about how legume variety selection affects cereal–legume intercrop performance under drought conditions. This study aims to test the hypothesis that positive rhizosphere interactions in faba bean–wheat intercrops will confer a “buffering capacity” on faba bean and wheat performance under water stress and that this effect will (i) depend on faba bean varietal selection and (ii) be enhanced with increasing faba bean varietal diversity. In a greenhouse experiment, three commercial faba bean (Vicia faba L.) varieties [Gloria (G), Alexia (A), Julia (J)] were grown in sole crop or intercropped with spring wheat (Triticum aestivum L.) under well-watered or water-stress conditions. Under intercropping, either one, two, or all three faba bean varieties were grown together with wheat to test the effect of intraspecific diversity on a cereal–legume intercrop performance. Consistent with the proposed hypothesis, we found that, under well-watered and water-stress conditions, wheat and faba bean shoot biomass production and nitrogen (N) acquisition improved with intercropping and that faba bean variety and variety mixture strongly modulated the intercropping effect. Interestingly, in both well-watered and water-stress conditions, wheat dry biomass and N accumulation were greatest in intercrops containing Gloria, while nodule number, nodule weight, and N accumulation in faba bean were greatest for intercrops containing Alexia and Julia (AJ). The effect of varietal diversity was inconsistent. Intercrops with two faba bean varieties tended to have positive or neutral effects on measured wheat and faba bean variables. However, overall performance under intercropping was generally reduced when all three faba bean varieties were planted with wheat. The effect of faba bean species diversity can buffer faba bean–wheat intercrop performance against water stress, and intercropping tended to have positive or neutral effects on the measured wheat and faba bean variables, notably with two-varietal faba bean mixtures.

Genotypic diversity weakens competition within, but not between, plant species

Abstract Intraspecific diversity can affect the ecological function of communities. Because community function is the outcome of species interactions, understanding how intraspecific diversity affects species interactions may shed light on the mechanism by which intraspecific diversity affects communities. Competition among and within plant species may be particularly important, as the relative strengths of these interactions can influence species coexistence and community stability. We established a field experiment in a New England salt marsh to determine how plant intraspecific diversity affects both intra‐ and interspecific competition. Focal plants of two species (Spartina alterniflora and Spartina patens) were planted with S. alterniflora neighbours that were either genotypically identical to one another (monoculture) or genotypically distinct (polyculture). After two growing seasons, S. alterniflora performance was enhanced in the presence of polyculture conspecific neighbours compared to monoculture neighbours, whereas S. patens was not strongly affected by diversity of its S. alterniflora neighbours. This suggests that intraspecific competition was weakened by intraspecific diversity, potentially even shifting to facilitation, but we did not find strong evidence of intraspecific diversity impacting interspecific competition. By weakening competition within species, intraspecific diversity may promote coexistence of genotypes within that species. Synthesis. The community‐level effects of intraspecific diversity may be mediated in part by its effect on intraspecific competition/facilitation. Furthermore, stronger intraspecific competition and decreased coexistence resulting from reduced diversity may exacerbate ongoing declines in biodiversity in response to global change.

Effects of intraspecific diversity on survivorship, growth, and recruitment of the eastern oyster across sites.

Intraspecific diversity, particularly of foundation species, can significantly affect population, community, and ecosystem processes. Examining how genetic diversity relates to demographic traits provides a key mechanistic link from genotypic and phenotypic variation of taxa with complex life histories to their population dynamics. We conducted a field experiment to assess how two metrics of intraspecific diversity (cohort diversity, the number of independent juvenile cohorts created from different adult source populations, and genetic relatedness, genetic similarity among individuals within and across cohorts) affect the survivorship, growth, and recruitment of the foundation species Crassostrea virginica. To assess the effects of both cohort diversity and genetic relatedness on oyster demographic traits under different environmental conditions, we manipulated juvenile oyster diversity and predator exposure (presence/absence of a cage) at two sites differing in resource availability and predation intensity. Differences in predation pressure between sites overwhelmingly determined post-settlement survivorship of oysters. However, in the absence of predation (i.e., cage treatment), one or both metrics of intraspecific diversity, in addition to site, influenced long-term survivorship, growth, and recruitment. While both cohort diversity and genetic relatedness were negatively associated with long-term survivorship, genetic relatedness alone showed a positive association with growth and cohort diversity alone showed a positive association with recruitment. Thus, our results demonstrate that in the absence of predation, intraspecific diversity can affect multiple demographic traits of a foundation species, but the relative importance of these effects depends on the environmental context. Moreover, the magnitude and direction of these effects vary depending on the diversity metric, cohort diversity or genetic relatedness, suggesting that although they are inversely related in this system, each captures sufficiently different components of intraspecific diversity. Given the global loss of oyster reef habitat and rapid decline in oyster population size, our results are particularly relevant to management and restoration. In addition, aquaculture, which commonly excludes predators during early life history stages, may benefit from incorporation of oyster cohort diversity into standard practice.

Intraspecific diversity regulates fungal productivity and respiration.

Individuals and not just species are key components of biodiversity, yet the relationship between intraspecific diversity and ecosystem functioning in microbial systems remains largely untested. This limits our ability to understand and predict the effects of altered genetic diversity in regulating key ecosystem processes and functions. Here, we use a model fungal system to test the hypothesis that intraspecific genotypic richness of Paxillus obscurosporus stimulates biomass and CO2 efflux, but that this is dependent on nitrogen supply. Using controlled experimental microcosms, we show that populations containing several genotypes (maximum 8) of the fungus had greater productivity and produced significantly more CO2 than those with fewer genotypes. Moreover, intraspecific diversity had a much stronger effect than a four-fold manipulation of the carbon:nitrogen ratio of the growth medium. The effects of intraspecific diversity were underpinned by strong roles of individuals, but overall intraspecific diversity increased the propensity of populations to over-yield, indicating that both complementarity and selection effects can operate within species. Our data demonstrate the importance of intraspecific diversity over a range of nitrogen concentrations, and the need to consider fine scale phylogenetic information of microbial communities in understanding their contribution to ecosystem processes.

Chloroplast DNA and biosystematics: The effects of intraspecific diversity and plastid transmission

SummaryHarris, S. A. & Ingram, R.: Chloroplast DNA and biosystematics: The effects of intraspecific diversity and plastid transmission. ‐ Taxon 40: 393–412. 1991. ‐ ISSN 0040‐0262.The widespread application of chloroplast DNA (cpDNA) to plant biosystematics is usually based on a number of assumptions. The assumption of low levels of intraspecific cpDNA variation is reviewed and the conclusion reached that far from being rare, intraspecific cpDNA variation is relatively common. The evidence for the assumption of predominantly maternal plastid transmission is also reviewed. In both of the cases some of the possible effects on phylogenetic reconstruction are considered.