Global patterns of insect herbivory in gap and understorey environments, and their implications for woody plant carbon storage

Insect herbivory is thought to favour carbon allocation to storage in juveniles of shade-tolerant trees. This argument assumes that insect herbivory in the understorey is sufficiently intense as to select for storage; however, understoreys might be less attractive to insect herbivores than canopy gaps, because of low resource availability and - at temperate latitudes - low temperatures. Although empirical studies show that shade-tolerant species in tropical forests do allocate more photosynthate to storage than their light-demanding associates, the same pattern has not been consistently observed in temperate forests. Does this reflect a latitudinal trend in the relative activity of insect herbivory in gap versus understorey environments? To date there has been no global review of the effect of light environment on insect herbivory in forests. We postulated that if temperature is the primary factor limiting insect herbivory, the effect of gaps on rates of insect herbivory should be more evident in temperate than in tropical forests; due to low growing season temperatures in the oceanic temperate forests of the Southern Hemisphere, the effect of gaps on insect herbivory rates should in turn be stronger there than in the more continental temperate climates of the Northern Hemisphere. We examined global patterns of insect herbivory in gaps versus understories through meta-analysis of 87 conspecific comparisons of leaf damage in contrasting light environments. Overall, insect herbivory in gaps was significantly higher than in the understorey; insect herbivory was 50% higher in gaps than in understoreys of tropical forests but did not differ significantly between gaps and understories in temperate forests of either hemisphere. Results are consistent with the idea that low resource availability - and not temperature - limits insect herbivore activity in forest understoreys, especially in the tropics, and suggest the selective influence of insect herbivory on late-successional tree species may have been over-estimated

The influence of hydrological regimes on sex ratios and spatial segregation of the sexes in two dioecious riparian shrub species in northern Sweden

River management practices have altered the hydrological regimes of many rivers and also altered the availability of regeneration niches for riparian species. We investigated the impact of changed hydrological regimes on the sex ratios and the Spatial Segregation of the Sexes (SSS) in the dioecious species Salix myrsinifolia Salisb.–phylicifolia L. and S. lapponum L. by studying the free-flowing Vindel River and the regulated Ume River in northern Sweden. We surveyed sex ratios of these species in 12 river reaches on the Vindel River and in 17 reaches on the Ume River. In addition, we surveyed the sex and location above mean river stage of 1,002 individuals across both river systems to investigate the SSS of both species. Cuttings were collected from male and female individuals of S. myrsinifolia–phylicifolia from both rivers and subjected to four different water table regimes in a greenhouse experiment to investigate growth response between the sexes. We found an M/F sex ratio in both river systems similar to the regional norm of 0.62 for S. myrsinifolia–phylicifolia and of 0.42 for S. lapponum. We found no evidence of SSS in either the free-flowing Vindel River or the regulated Ume River. In the greenhouse experiment, hydrological regime had a significant effect on shoot and root dry weight and on root length. Significantly higher shoot dry weights were found in females than in males and significantly different shoot and root dry weights were found between cuttings taken from the two rivers. We concluded that changed hydrological regimes are likely to alter dimensions of the regeneration niche and therefore to influence sex ratios and SSS at an early successional stage, making it difficult to find clear spatial patterns once these species reach maturity and can be sexed

Pollen Competition as a Reproductive Isolation Barrier Represses Transgene Flow between Compatible and Co-Flowering Citrus Genotypes

Background/Objective: Despite potential benefits granted by genetically modified (GM) fruit trees, their release and commercialization raises concerns about their potential environmental impact, and the transfer via pollen of transgenes to cross-compatible cultivars is deemed to be the greatest source for environmental exposure. Information compiled from field trials on GM trees is essential to propose measures to minimize the transgene dispersal. We have conducted a field trial of seven consecutive years to investigate the maximum frequency of pollen-mediated crop-to-crop transgene flow in a citrus orchard, and its relation to the genetic, phenological and environmental factors involved. Methodology/Principal Findings: Three different citrus genotypes carrying the uidA (GUS) tracer marker gene (pollen donors) and a non-GM self-incompatible contiguous citrus genotype (recipient) were used in conditions allowing natural entomophilous pollination to occur. The examination of 603 to 2990 seeds per year showed unexpectedly low frequencies (0.17-2.86%) of transgene flow. Paternity analyses of the progeny of subsets of recipient plants using 10 microsatellite (SSR) loci demonstrated a higher mating competence of trees from another non-GM pollen source population that greatly limited the mating chance of the contiguous cross-compatible and flowering-synchronized transgenic pollen source. This mating superiority could be explained by a much higher pollen competition capacity of the non-GM genotypes, as was confirmed through mixed-hand pollinations. Conclusions/Significance: Pollen competition strongly contributed to transgene confinement. Based on this finding, suitable isolation measures are proposed for the first time to prevent transgene outflow between contiguous plantings of citrus types that may be extendible to other entomophilous transgenic fruit tree species. (Résumé d'auteur

CREATING AN UNDERGRADUATE CULTURE OF SCIENCE BY INTEGRATING INQUIRY, PROJECT-BASED LEARNING, AND RESEARCH INTO THE CURRICULUM

Full engagement in science includes observation and asking questions, the development of a hypothesis, designing and conducting an appropriate experiment to test that hypothesis, data acquisition, appropriate analysis, revisiting initial questions, and dissemination of results. Here, I report on efforts to engage undergraduate students in all of these elements of science by integrating inquiry, investigation, and research in four intermediate biology courses for all majors. The project-based courses include Plant Ecology, Scanning Electron Microscopy, Molecular Genetics, and Physiological Ecology. Students conduct semester-long, experimental research projects and present their results at a public poster session on campus. Using computers, peripherals, and software funded by an award from the National Science Foundation, efforts were made to enhance the data acquisition, analysis, and presentation aspects of student research. The quality of the student research was improved, and student pride and ownership over the work increased. Students exhibited a greater understanding of science and quantitative analysis. One student project was published in a peer-reviewed journal, and many others were presented at regional and national meetings. The number of students taking elective courses in related areas, continuing research and senior honors projects, and applying and being accepted to related graduate programs significantly increased. Student poster sessions served to create a campuswide culture of science

The Integration of Conservation, Biodiversity, and Sustainability

Our understanding of conservation biology and sustainability have been independently developing for a long time. Evidence suggests that biodiversity is critical for ecosystem function and services on which humans depend, and is directly linked to the economic, social, and environmental components of sustainability. Because of this, the integration of research from each of these areas should and is becoming a priority. In this article, the development of each of these fields and, ultimately, their integration are reviewed. From this, a number of research priorities that allow for the transition from conflict to mutual compatibility between conservation and sustainability objectives are explored. These priorities include research that will improve our understanding of (1) ecosystem services and function provided by biodiversity that benefit humans; (2) the connection between biodiversity and poverty reduction; (3) biodiverse agriculture; (4) issues surrounding indigenous knowledge; and (5) the development of indicators that allow for the integrative assessment of biodiversity conservation and sustainability objectives

The reproductive ecology of the dioecious shrub Lindera benzoin L. Blume (Lauraceae) in sun and shade habitats

Understory plants can occur in a wide range of light conditions. The effects of light environment on the pre- and post-pollination reproductive ecology of the dioecious understory shrub Lindera benzoin L. Blume (Lauraceae) were examined in a variety of field studies. Pre-pollination studies revealed that sex ratio was always 1:1; but flower production was greater in the sun than in the shade, and greater for male plants than for females in both habitat types. The population level ratio of pollen to ovules (P/O) was greater in the shade than in the sun, but pollinator abundance was a more important determinant of pollen deposition than P/O. Fruit set was significantly greater in the sun than in the shade, and was reduced in both habitats by artificially shading branches. Supplemental pollination added significantly more viable pollen to stigmas, but had no effect on fruit set, even under conditions of high light availability. Treatments did result in a significant reduction in per branch flower production, especially on fruit bearing branches in shade sites and on artificially shaded branches. Defoliations at the level of the branch significantly reduced fruit maturation. The gametophytic competition hypothesis which predicts that a plant should selectively mature fruits from flowers experiencing the highest levels of pollen tube competition was tested by examining the probability of fruit maturation as a function of pollen tube number. Styles were removed soon after the period of stigma receptivity, and the subsequent fate of the flowers was monitored. Flowers that eventually matured fruits had significantly more pollen tubes per style than those that initiated but then aborted fruits, supporting the hypothesis. The effects of gender and light environment on rates of herbivory and growth were explored. Herbivory was greater in shade habitats than in sun habitats, and vegetative plants suffered greater herbivory per leaf area than males or females which did not differ in the amount of leaf material eaten. Branch growth rates were higher in the sun than in the shade, and females grew less than male or vegetative plants

The influence of climate warming on flowering phenology in relation to historical annual and seasonal temperatures and plant functional traits

Climate warming has the potential to influence plant flowering phenology which in turn can have broader ecological consequences. Herbarium collections offer a source of historical plant data that makes possible the ability to document and better understand how warming climate can influence long-term shifts in flowering phenology. We examined the influence of annual, winter, and spring temperatures on the flowering phenology of herbarium specimens for 36 species collected from 1884–2015. We then compared the response to warming between native and non-native, woody and herbaceous, dry and fleshy fruit, and spring vs summer blooming species. Across all species, plants flowered 2.26 days earlier per 1 °C increase in annual average temperatures and 2.93 days earlier per 1 °C increase in spring onset average temperatures. Winter temperatures did not significantly influence flowering phenology. The relationship of temperature and flowering phenology was not significantly different between native and non-native species. Woody species flowered earlier than herbaceous species only in response to increasing annual temperatures. There was no difference in the phenological response between species with dry fruits and those fleshy fruits for any of the temperature periods. Spring blooming species exhibited a significantly greater phenological response to warming yearly average temperatures than summer blooming species. Although herbarium specimens can reveal climate change impacts on phenology, it is also evident that the phenological responses to warming vary greatly among species due to differences in functional traits such as those considered here, as well as other factors

Appendix A. Statistical results from analyses of population-specific responses to light for herbivory and photosynthesis-related traits in Lindera benzoin.

Statistical results from analyses of population-specific responses to light for herbivory and photosynthesis-related traits in Lindera benzoin