Ethanol produced from cellulosic biomass is examined as a large-scale transportation fuel. Desirable features include ethanol's fuel properties as well as benefits with respect to urban air quality, global climate change, balance of trade, and energy security. Energy balance, feedstock supply, and environmental impact considerations are not seen as significant barriers to the widespread use of fuel ethanol derived from cellulosic biomass. Conversion economics is the key obstacle to be overcome. In light of past progress and future prospects for research-driven improvements, a cost-competitive process appears possible in a decade.

Using published distributions of 65 species from the British Isles and northern Europe, we show that ant assemblages change with latitude in two ways. First, as commonly found for many types of organisms, the number of ant species decreased significantly with increasing latitude. For Ireland and Great Britain, species richness also increased significantly with region area. Second, although rarely demonstrated for ectotherms, the body size of ant species, as measured by worker length, increased significantly with increasing latitude. We found that this body-size pattern existed in the subfamily Formicinae and, to a lesser extent, in the Myrmicinae, which together comprised 95% of the ant species in our study area. There was a trend for formicines to increase in size with latitude faster than myrmicines. We also show that the pattern of increasing body size was due primarily to the ranges of ant species shifting to higher latitudes as their body sizes increased, with larger formicines becoming less represented at southerly latitudes and larger myrmicines becoming more represented at northerly latitudes. We conclude by discussing five potential mechanisms for generating the observed body-size patterns: the heat-conservation hypothesis, two hypotheses concerning phylogenetic history, the migration-ability hypothesis, and the starvation-resistance hypothesis.

Abstract. We examined the impact of a tending ant, Formica altipetens, on the population dynamics of a membracid, Publilia modesta. Controlled ant-exclusion experiments revealed three ways in which the strength and occurrence of this mutualism was conditional. First, we detected yearly variation in the impact of ants on membracids. Ants had a significant positive impact on membracid abundance in 1985 and 1987, but not in 1986. Second, we found age-specific effects of ants on membracids. In 1985 and 1987 our experiments revealed that only membracid nymphs benefit directly from ant tending; we did not detect a direct positive impact of ants on the survival of membracid adults in any year. Third, we documented a density-dependent effect of ants on membracids. In 1985 and 1987, nymphs in large aggregations benefited from ant tending more than nymphs in small aggregations.Observations in 1985-1987 suggest that protection from a predatory salticid spider, Pellenes sp., may be at least one mechanism by which ants benefit membracid nymphs. In 1985 and 1987, when the association was mutualistic, spiders were significantly more abundant on membracid-infested plants without ants than on infested plants with ants, whereas this was not the case in 1986. We hypothesize that the age-specific benefits in this system may result because nymphs are especially susceptible to predation by spiders whereas the more agile and sclerotized adults are not.

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Abstract. Biological invasions are a global phenomenon that can accelerate disturbance regimes and facilitate colonization by other nonnative species. In a coastal grassland in northern California, we conducted a four-year exclosure experiment to assess the effects of soil disturbances by feral pigs (Sus scrofa) on plant community composition and soil nitrogen availability. Our results indicate that pig disturbances had substantial effects on the community, although many responses varied with plant functional group, geographic origin (native vs. exotic), and grassland type. (''Short patches'' were dominated by annual grasses and forbs, whereas ''tall patches'' were dominated by perennial bunchgrasses.) Soil disturbances by pigs increased the richness of exotic plant species by 29% and native taxa by 24%. Although native perennial grasses were unaffected, disturbances reduced the biomass of exotic perennial grasses by 52% in tall patches and had no effect in short patches. Pig disturbances led to a 69% decrease in biomass of exotic annual grasses in tall patches but caused a 62% increase in short patches. Native, nongrass monocots exhibited the opposite biomass pattern as those seen for exotic annual grasses, with disturbance causing an 80% increase in tall patches and a 56% decrease in short patches. Native forbs were unaffected by disturbance, whereas the biomass of exotic forbs increased by 79% with disturbance in tall patches and showed no response in short patches. In contrast to these vegetation results, we found no evidence that pig disturbances affected nitrogen mineralization rates or soil moisture availability. Thus, we hypothesize that the observed vegetation changes were due to space clearing by pigs that provided greater opportunities for colonization and reduced intensity of competition, rather than changes in soil characteristics. In summary, although responses were variable, disturbances by feral pigs generally promoted the continued invasion of this coastal grassland by exotic plant taxa.

Biological invasion by nonnative species is a global phenomenon that has the capacity to dramatically alter native communities. However, surprisingly few studies have quantified the effects of exotic plant species on the communities they invade, or have considered how these effects vary among habitat types or seasons. Here, we used both comparative and experimental field studies to investigate the influence of Cape ivy (Delairea odorata; Asteraceae), an invasive evergreen vine native to South Africa, on three habitat types in coastal regions of northern California (coastal scrub, willow riparian, and alder riparian). In the comparative study, plots invaded by Cape ivy contained 36% fewer native plant species and 37% fewer nonnative taxa, and this pattern persisted across habitat types and seasons. The richness of grass and forb species was lower in invaded plots, whereas fern and shrub richness did not vary among zones. Native species richness was significantly lower with increasing cover of Cape ivy, but this was not the case for nonnative species. In addition, invasion by Cape ivy was associated with a 31% decrease in species diversity as well as an 88% decrease in the abundance of native seedlings and a 92% decrease in nonnative seedlings compared to uninvaded areas. After 2 yr, a Cape-ivy reduction experiment yielded similar results, with a 10% increase in the richness of native species compared to control plots, and a 43% increase in the richness of nonnative taxa. Forb species richness increased significantly when Cape-ivy cover was reduced, whereas shrub richness decreased slightly and no effects were detected for ferns and grasses. We also found that Cape-ivy reduction led to a 32% increase in plant species diversity, an 86% increase in the abundance of native seedlings, and an 85% increase for nonnative seedlings. In all cases, the effects of Cape-ivy reduction were consistent across habitat types. Collectively, our results indicate that this invader has significantly changed the composition of three different habitat types, and its control should be a major priority. However, our data also indicate that Cape ivy had negative effects on the richness of both native and nonnative plant species. Such findings suggest that a consequence of removing Cape ivy from invaded areas may be to facilitate the proliferation of other nonnative species.

Wild large herbivores are declining worldwide. Despite extensive use of exclosure experiments to investigate herbivore impacts, there is little consensus on the effects of wild large herbivores on ecosystem function. Of the ecosystem functions likely impacted, we reviewed the five most‐studied in exclosure experiments: ecosystem resilience/resistance to disturbance, nutrient cycling, carbon cycling, plant regeneration, and primary productivity. Experimental data on large wild herbivores' effects on ecosystem functions were predominately derived from temperate grasslands (50% grasslands, 75% temperate zones). Additionally, data were from experiments that may not be of adequate size (median size 400 m2 despite excluding all experiments below 25 m2) or duration (median duration 6 years) to capture ecosystem‐scale responses to these low‐density and wide‐ranging taxa. Wild herbivore removal frequently impacted ecosystem functions; for example, net carbon uptake increased by three times in some instances. However, the magnitude and direction of effects, even within a single function, were highly variable. A focus on carbon cycling highlighted challenges in interpreting effects on a single function. While the effect of large herbivore exclusion on carbon cycling was slightly positive when its components (e.g. pools vs. fluxes of carbon) were aggregated, effects on individual components were variable and sometimes opposed. Given modern declines in large wild herbivores, it is critical to understand their effects on ecosystem function. However, this synthesis highlights strong variability in direction, magnitude, and modifiers of these effects. Some variation is likely due to disparity in what components are used to describe a given function. For example, for the carbon cycle we identified eight distinctly meaningful components, which are not easily combined yet are potentially misrepresentative of the larger cycle when considered alone. However, much of the observed difference in responses likely reflects real ecological variability across complex systems. To move towards a general predictive framework we must identify where variation in effect is due to methodological differences and where due to ecosystem context. Two critical steps forward are (a) additional quantitative synthetic analyses of large herbivores' effects on individual functions, and (b) improved, increased systematic exclosure research focusing on effects of large herbivores' exclusion on functions. A free Plain Language Summary can be found within the Supporting Information of this article.

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