Code Puzzle Completion Problems in Support of Learning Programming Independently

Middle school children often lack access to formal educational opportunities to learn computer programming. One way to help these children may be to provide tools that enable them to learn programming on their own independently. However, in order for these tools to be effective they must help learners acquire programming knowledge and also be motivating in independent contexts. I explore the design space of using motivating code puzzles with a method known to support independent learning: completion problems. Through this exploration, I developed code puzzle completion problems and an introductory curriculum introducing novice programmers to basic programming constructs. Through several evaluations, I demonstrate that code puzzle completion problems can motivate learners to acquire new programming knowledge independently. Specifically, I found that code puzzle completion problems are more effective and efficient for learning programming constructs independently compared to tutorials. Puzzle users performed 33% better on transfer tasks compared to tutorial users, while taking 21% less time to complete the learning materials. Additionally, I present evidence that children are motivated to choose to use the code puzzles because they find the experience enjoyable, challenging, and valuable towards developing their programming skills. Given the choice between using tutorials and puzzles, only 10% of participants opted to use more tutorials than puzzles. Further, 80% of participants also stated a preference towards the puzzles because they simply enjoyed the experience of using puzzles more than the tutorials. The results suggest that code puzzle completion problems are a promising approach for motivating and supporting independent learning of programming

Resource‐based habitat associations in a neotropical liana community

Summary 1. Lianas are a conspicuous element of many tropical forests, accounting for up to 40% of woody stem density and 20% of species richness in seasonal forests. However, lianas have seldom been surveyed at sufficiently large spatial scales to allow an assessment of the importance of habitat variables in structuring liana communities. 2. We compare the association patterns of 82 liana species and an equivalent sample of tree species on the 50 ha Forest Dynamics Project plot on Barro Colorado Island, Panama, with topographic habitat variables (high and low plateau, slope, swamp and streamside), and thirteen mapped soil chemical variables. In addition, we test for liana species associations with canopy disturbance using a canopy height map of the plot generated using light detection and ranging. 3. For all liana species combined, densities differed among topographic habitat types in the plot, with significantly higher densities on the seasonally drier lower plateau habitat (1044 individuals ha−1) than the moister slope habitat (729 individuals ha−1). Lianas were also significantly more abundant than expected in areas with low canopy height. 4. The proportion of liana species associated with one or more topographic habitat variables (44%) was significantly lower than that for trees (66%). Similarly, liana species were significantly less frequently associated with PC axes derived from soil chemical variables (21%) than trees (52%). The majority of liana species (63%) were significantly associated with areas of the plot with low canopy height reflecting an affinity for treefall gaps. 5. Synthesis. The habitat associations detected here suggest that liana density is associated primarily with canopy disturbance, and to a lesser extent with topography and soil chemistry. Relative to trees, few liana species were associated with local variation in topography and soil chemistry, suggesting that nutrient availability exerts only weak effects on liana community composition compared to trees. Results from this study support the contention that increases in forest disturbance rates are a driver of recently observed increases in liana abundance and biomass in neotropical forests

Soil resources and topography shape local tree community structure in tropical forests

Both habitat filtering and dispersal limitation influence the compositional structure of forest communities, but previous studies examining the relative contributions of these processes with variation partitioning have primarily used topography to represent the influence of the environment. Here, we bring together data on both topography and soil resource variation within eight large (24-50 ha) tropical forest plots, and use variation partitioning to decompose community compositional variation into fractions explained by spatial, soil resource and topographic variables. Both soil resources and topography account for significant and approximately equal variation in tree community composition (9-34% and 5-29%, respectively), and all environmental variables together explain 13-39% of compositional variation within a plot. A large fraction of variation (19-37%) was spatially structured, yet unexplained by the environment, suggesting an important role for dispersal processes and unmeasured environmental variables. For the majority of sites, adding soil resource variables to topography nearly doubled the inferred role of habitat filtering, accounting for variation in compositional structure that would previously have been attributable to dispersal. Our results, illustrated using a new graphical depiction of community structure within these plots, demonstrate the importance of small-scale environmental variation in shaping local community structure in diverse tropical forests around the globe. © 2012 The Author(s) Published by the Royal Society. All rights reserved

Nonrandom processes maintain diversity in tropical forests

An ecological community\u27s species diversity tends to erode through time as a result of stochastic extinction, competitive exclusion, and unstable host-enemy dynamics. This erosion of diversity can be prevented over the short term if recruits are highly diverse as a result of preferential recruitment of rare species or, alternatively, if rare species survive preferentially, which increases diversity as the ages of the individuals increase. Here, we present census data from seven New and Old World tropical forest dynamics plots that all show the latter pattern. Within local areas, the trees that survived were as a group more diverse than those that were recruited or those that died. The larger (and therefore on average older) survivors were more diverse within local areas than the smaller survivors. When species were rare in a local area, they had a higher survival rate than when they were common, resulting in enrichment for rare species and increasing diversity with age and size class in these complex ecosystems

Comparing tropical forest tree size distributions with the predictions of metabolic ecology and equilibrium models

Tropical forests vary substantially in the densities of trees of different sizes and thus in above-ground biomass and carbon stores. However, these tree size distributions show fundamental similarities suggestive of underlying general principles. The theory of metabolic ecology predicts that tree abundances will scale as the -2 power of diameter. Demographic equilibrium theory explains tree abundances in terms of the scaling of growth and mortality. We use demographic equilibrium theory to derive analytic predictions for tree size distributions corresponding to different growth and mortality functions. We test both sets of predictions using data from 14 large-scale tropical forest plots encompassing censuses of 473 ha and \u3e 2 million trees. The data are uniformly inconsistent with the predictions of metabolic ecology. In most forests, size distributions are much closer to the predictions of demographic equilibrium, and thus, intersite variation in size distributions is explained partly by intersite variation in growth and mortality. © 2006 Blackwell Publishing Ltd/CNRS

Testing metabolic ecology theory for allometric scaling of tree size, growth and mortality in tropical forests

The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 old-growth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory's predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests

Interactions between all pairs of neighboring trees in 16 forests worldwide reveal details of unique ecological processes in each forest, and provide windows into their evolutionary histories

When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands’ physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees’ distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions