The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Ecological and evolutionary consequences of Allee effects in small founder populations of invasive species

2011 Summer.Includes bibliographical references.Despite the obvious threats invasive species pose to ecosystem health, studying the characteristics that influence their colonization can provide valuable insight on fundamental issues in ecology, evolution, and biogeography. The aim of this research has been focused on the implications of mechanisms likely to affect persistence of small founder populations. Individuals can suffer a reduction in one or more components of fitness when population growth and spread are constrained at low density. This dynamical relationship between fitness and population size (i.e., positive density dependence) can be driven by a myriad of mechanisms, broadly termed Allee effects. In this dissertation, I have theoretically explored how small founder populations faced with Allee effects can overcome the demographic challenges that heighten the risk of extinction. I have developed models of increasing complexity to better understand the ecological and evolutionary consequences of Allee effects. I begin by exploring ways in which intraspecific interactions influence population dynamics and invasiveness through a review of the literature. The mechanisms that impact individual fitness at low density suggest that there are benefits to being in a large population; however, there are abundant examples of adaptations that might have evolved in small or sparse populations in response to Allee effects. Using a reaction-diffusion framework with a quantitative genetics approach, I have derived conditions and explored the dynamics for rapid adaptive evolution rescuing the population from extinction. This deterministic modeling approach broadly describes population dynamics through diffusive dispersal and density dependent growth, where the response to population density can evolve through a genetic subsystem that incorporates the intensity of selection and genetic variance. For both the spatial and non-spatial cases, invasion criteria were determined across the range of parameter space. The results emphasized that a sufficient amount of genetic variance is a crucial component for evolutionary rescue to occur. I developed a spatially explicit, individual-based stochastic simulation in order to more realistically capture the complexity of intraspecific interactions. I found that with limited dispersal and local perception, the emergence of spatial structure impacted individual fitness and could enable population persistence. Departures from the population-level model predictions demonstrate the importance of considering individual variation in assessing the consequences of Allee effects. I further incorporated immigration and genetic variation into the simulation in order to explore the relative importance of evolutionary, demographic, and genetic rescue for establishment. Additional immigration was more effective than adaptive evolution in contributing to successful invasions due to the intensity of ecological constraints on population growth and time to extinction. Without multiple introductions, evolutionary processes can contribute to recovery through genetic variation maintained and enhanced by mutation and recombination. Overall, I have demonstrated that it is possible for a small founder population to overcome a suite of ecological, evolutionary, and genetic obstacles upon introduction into a novel environment despite the paradox of invasion

To play or not to play? That’s a resource abundance question

Although play occurs in a wide variety of animals, models of the origins of play behavior are lacking. We propose a novel computational model exploring the evolution of non-social frivolous play. Asexually reproducing semelparous animals can either rest or forage. Foraging occurs when an organism is below an energy threshold. Success is determined by the combination of skill and availability of resources, which declines over time but replenishes for each generation. Play was introduced as a mutant strategy: a frivolous activity that uses energy and increases the probability of dying over resting with no direct fitness benefit. Simulations show that play behavior becomes fixed in the population and the time spent playing is maintained at a low rate in spite of its costly nature. When play behavior is functional by increasing foraging ability, it evolves quickly and the time individuals spend playing increases, but eventually the population of players collapses and play disappears. We suggest a mechanism underlying the origins of adaptive play from non-adaptive behavior when resources expand. Initially play acts as a spiteful behavior in that playing individuals suffer a direct cost to their fitness, but also may incur even greater costs to other individuals in the population

Using network properties to predict disease dynamics on human contact networks

Recent studies have increasingly turned to graph theory to model more realistic contact structures that characterize disease spread. Because of the computational demands of these methods, many researchers have sought to use measures of network structure to modify analytically tractable differential equation models. Several of these studies have focused on the degree distribution of the contact network as the basis for their modifications. We show that although degree distribution is sufficient to predict disease behaviour on very sparse or very dense human contact networks, for intermediate density networks we must include information on clustering and path length to accurately predict disease behaviour. Using these three metrics, we were able to explain more than 98 per cent of the variation in endemic disease levels in our stochastic simulations

Indirect effects of parasites in invasions

1. Introduced species disrupt native communities and biodiversity worldwide. Parasitic infections (and at times, their absence) are thought to be a key component in the success and impact of biological invasions by plants and animals. They can facilitate or limit invasions, and positively or negatively impact native species. 2. Parasites have not only direct effects on their hosts, but also indirect effects on the species with which their hosts interact. Indirect effects include density-mediated effects (resulting from parasite-induced reduction in host reproduction and survival) as well as trait-mediated indirect effects (resulting from parasite-induced changes in host phenotype, behavior or life history). These effects are not mutually exclusive but often interact. 3. The importance of these indirect interactions for invasion success, and the extent to which these effects ramify throughout communities and influence ecosystems undergoing biological invasion provide the focus of our review. Examples from the animal and plant literature illustrate the importance of parasites in mediating both competitive and consumer–resource interactions between native and invasive species. 4. Parasites are involved in indirect interactions at all trophic levels. Furthermore, the indirect effects of parasitic infection are important at a range of biological scales from within a host to the whole ecosystem in determining invasion success and impact. 5. To understand the importance of parasitic infection in invasion success and in the outcomes for invaded communities requires an interdisciplinary approach by ecologists and parasitologists, across animal and plant systems. Future research should develop a framework integrating community ecology, evolution and immunology to better understand and manage the spread of invasive species and their diseases

Do invasive species perform better in their new ranges?

A fundamental assumption in invasion biology is that most invasive species exhibit enhanced performance in their introduced range relative to their home ranges. This idea has given rise to numerous hypotheses explaining “invasion success” by virtue of altered ecological and evolutionary pressures. There are surprisingly few data, however, testing the underlying assumption that the performance of introduced populations, including organism size, reproductive output, and abundance, is enhanced in their introduced compared to their native range. Here, we combined data from published studies to test this hypothesis for 26 plant and 27 animal species that are considered to be invasive. On average, individuals of these 53 species were indeed larger, more fecund, and more abundant in their introduced ranges. The overall mean, however, belied significant variability among species, as roughly half of the investigated species (N = 27) performed similarly when compared to conspecific populations in their native range. Thus, although some invasive species are performing better in their new ranges, the pattern is not universal, and just as many are performing largely the same across ranges

Appendix A. Hierarchical Bayesian model description, tables of pooling factors, and figures showing WW/BIO contrasts and coefficient of variation in the introduced vs. native range.

Hierarchical Bayesian model description, tables of pooling factors, and figures showing WW/BIO contrasts and coefficient of variation in the introduced vs. native range