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The effect of consumers on their resources has been demonstrated in many systems but is often confounded by trophic interactions with other consumers. Consumers may also have behavioral and life history adaptations to each other and to co-occurring predators that may additionally modulate their particular roles in ecosystems. We experimentally excluded large consumers from tile periphyton, leaves and natural benthic substrata using submerged electrified frames in three stream reaches with overlapping consumer assemblages in Trinidad, West Indies. Concurrently, we assessed visits to (non-electrified) control frames by the three most common large consumers-primarily insectivorous killifish (Rivulus hartii), omnivorous guppies (Poecilia reticulata) and omnivorous crabs (Eudaniela garmani). Consumers caused the greatest decrease in final chlorophyll a biomass and accrual rates the most in the downstream reach containing all three focal consumers in the presence of fish predators. Consumers also caused the greatest increase in leaf decay rates in the upstream reach containing only killifish and crabs. In the downstream reach where guppies co-occur with predators, we found significantly lower benthic invertebrate biomass in control relative to exclosure treatments than the midstream reach where guppies occur in the absence of predators. These data suggest that differences in guppy foraging, potentially driven by differences in their life history phenotype, may affect ecosystem structure and processes as much as their presence or absence and that interactions among consumers may further mediate their effects in these stream ecosystems.

Allochthonous inputs of detritus represent an important energy source for streams in forested regions, but dynamics of these materials are not well studied in neotropical headwater streams. As part of the tropical amphibian declines in streams (TADS) project, we quantified benthic organic matter standing stocks and organic seston dynamics in four Panamanian headwater streams, two with (pre-amphibian decline) and two without (post-decline) healthy amphibian assemblages. We also measured direct litterfall and lateral litter inputs in two of these streams. Continuous litterfall and monthly benthic samples were collected for 1 year, and seston was collected 1-3 times/month for 1 year at or near baseflow. Direct litterfall was similar between the two streams examined, ranging from 934-1,137 g DM m⁻² y⁻¹. Lateral inputs were lower, ranging from 140-187 g DM m⁻¹ y⁻¹. Dead leaves (57-60%), wood (24-29%), and green leaves (8-9%) contributed most to inputs, and total inputs were generally higher during the rainy season. Annual habitat-weighted benthic organic matter standing stocks ranged from 101-171 g AFDM m⁻² across the four study reaches, with ~4 x higher values in pools compared to erosional habitats. Total benthic organic matter (BOM) values did not change appreciably with season, but coarse particulate organic matter (CPOM, >1 mm) generally decreased and very fine particulate organic matter (VFPOM, 1.6-250 μm) generally increased during the dry season. Average annual seston concentrations ranged from 0.2-0.6 mg AFDM l⁻¹ (fine seston, <754 μm >250 μm) and 2.0-4.7 mg AFDM l⁻¹ (very fine, <250 μm >1.6 μm), with very fine particles composing 85-92% of total seston. Quality of fine seston particles in the two reaches where tadpoles were present was significantly higher (lower C/N) than the two where tadpoles had been severely reduced (P = 0.0028), suggesting that ongoing amphibian declines in this region are negatively influencing the quality of particles exported from headwaters. Compared to forested streams in other regions, these systems receive relatively high amounts of allochthonous litter inputs but have low in-stream storage.

Amphibians can be important consumers in both aquatic and terrestrial habitats and may represent an important energetic link between the two, particularly in the tropics, where amphibian species richness and abundance are high. In the past 20 years, amphibian populations have declined dramatically around the world; numbers have decreased catastrophically in protected upland sites throughout the neotropics, usually resulting in the disappearance of over 75% of amphibians at a given site, particularly those species that breed in streams. Most studies of amphibian declines have focused on identifying causes and documenting changes in adult abundance, rather than on their ecological consequences. Here, we review evidence for the potential ecological effects of catastrophic amphibian declines, focusing on neotropical highland streams, where impacts will likely be greatest. Evidence to date suggests that amphibian declines will have large-scale and lasting ecosystem-level effects, including changes in algal community structure and primary production, altered organic matter dynamics, changes in other consumers such as aquatic insects and riparian predators, and reduced energy transfers between streams and riparian habitats. Furthermore, because of habitat and functional differences between larvae and adults in most amphibians, the loss of a single species is akin to losing two species.

As part of the Tropical Amphibian Declines in Streams (TADS) project, we estimated macroinvertebrate production and constructed quantitative food webs for four headwater stream reaches in the Panamanian uplands: two that had experienced massive amphibian declines and two with unaffected amphibian populations. As expected for forested headwaters, allochthonous materials were the dominant energy source. Total macroinvertebrate biomass and production ranged from 231 to 360 mg ash-free dry mass m⁻² and from 3.1 to 4.4 g ash-free dry mass m⁻² y⁻¹, respectively, and did not appear influenced by the presence or absence of amphibians. However, macroinvertebrate functional structure differed between pre- and post-decline sites, with shredder production significantly higher in pre-decline sites and scrapers significantly higher in post-decline sites. Taxonomic differences between pre- and post-decline sites were also evident. There was a shift in scrapers from smaller-bodied taxa (e.g., Psephenus) in pre-decline sites to larger-bodied groups (e.g., Petrophila) in post-decline sites. Detrital pathways were dominant in these systems, with shredders and collectors accounting for most energy flow. However, scrapers were well-represented and they were food-limited in these systems, particularly in the presence of larval amphibians at pre-decline sites. Ecological effects of catastrophic amphibian declines ranged from subtle shifts in taxonomic composition and functional structure of remaining consumers to changes in the availability and relative importance of autochthonous energy sources.

A proactive sampling strategy was designed and implemented in 2000 to document changes in streams whose catchment land uses were predicted to change over the next two decades due to increased building density. Diatoms, macroinvertebrates, fishes, suspended sediment, dissolved solids, and bed composition were measured at two reference sites and six sites where a socioeconomic model suggested new building construction would influence stream ecosystems in the future; we label these “hazard sites.” The six hazard sites were located in catchments with forested and agricultural land use histories. Diatoms were species-poor at reference sites, where riparian forest cover was significantly higher than all other sites. Cluster analysis, Wishart's distance function, non-metric multidimensional scaling, indicator species analysis, and t-tests show that macroinvertebrate assemblages, fish assemblages, in situ physical measures, and catchment land use and land cover were different between streams whose catchments were mostly forested, relative to those with agricultural land use histories and varying levels of current and predicted development. Comparing initial results with other regional studies, we predict homogenization of fauna with increased nutrient inputs and sediment associated with agricultural sites where more intense building activities are occurring. Based on statistical separability of sampled sites, catchment classes were identified and mapped throughout an 8,600 km² region in western North Carolina's Blue Ridge physiographic province. The classification is a generalized representation of two ongoing trajectories of land use change that we suggest will support streams with diverging biota and physical conditions over the next two decades.

Southern African genomes The complete genome sequences of an indigenous hunter-gatherer from Namibia's Kalahari Desert and of a Bantu from South Africa are presented in this issue, together with protein-coding regions from three other hunter-gatherer groups from the Kalahari. Analysis of genetic variance in what is probably the oldest known modern human lineage will contribute to understanding human diversity, and facilitate the inclusion of southern Africans in medical genomics research projects. Initial observations from the data include the fact that the Bushmen seem more different from each other, in terms of nucleotide substitutions, than typical Asians and Europeans. More speculatively, variants between these genomes and the existing data sets may point to genetic adaptations for an agricultural lifestyle. Until now, fully sequenced human genomes of the indigenous hunter-gatherer peoples of southern Africa have been limited to recently diverged populations. The complete genome sequences of an indigenous hunter-gatherer from the Kalahari Desert and of a Bantu from southern Africa are now presented. The extent of whole-genome and exome diversity is characterized; the observed genomic differences may help to pinpoint genetic adaptations to an agricultural lifestyle. The genetic structure of the indigenous hunter-gatherer peoples of southern Africa, the oldest known lineage of modern human, is important for understanding human diversity. Studies based on mitochondrial 1 and small sets of nuclear markers 2 have shown that these hunter-gatherers, known as Khoisan, San, or Bushmen, are genetically divergent from other humans 1 , 3 . However, until now, fully sequenced human genomes have been limited to recently diverged populations 4 , 5 , 6 , 7 , 8 . Here we present the complete genome sequences of an indigenous hunter-gatherer from the Kalahari Desert and a Bantu from southern Africa, as well as protein-coding regions from an additional three hunter-gatherers from disparate regions of the Kalahari. We characterize the extent of whole-genome and exome diversity among the five men, reporting 1.3 million novel DNA differences genome-wide, including 13,146 novel amino acid variants. In terms of nucleotide substitutions, the Bushmen seem to be, on average, more different from each other than, for example, a European and an Asian. Observed genomic differences between the hunter-gatherers and others may help to pinpoint genetic adaptations to an agricultural lifestyle. Adding the described variants to current databases will facilitate inclusion of southern Africans in medical research efforts, particularly when family and medical histories can be correlated with genome-wide data.

Planning and decision-making can be improved by access to reliable forecasts of ecosystem state, ecosystem services, and natural capital. Availability of new data sets, together with progress in computation and statistics, will increase our ability to forecast ecosystem change. An agenda that would lead toward a capacity to produce, evaluate, and communicate forecasts of critical ecosystem services requires a process that engages scientists and decision-makers. Interdisciplinary linkages are necessary because of the climate and societal controls on ecosystems, the feedbacks involving social change, and the decision-making relevance of forecasts.

We applied an integrative framework to illuminate and discuss the complexities of exurbanization in Macon County, North Carolina. The case of Macon County, North Carolina, highlights the complexity involved in addressing issues of exurbanization in the Southern Appalachian region. Exurbanization, the process by which urban residents move into rural areas in search of unique natural amenities and idealized lifestyles, can often have a dramatic impact on the local economy, culture, and environment. Within Macon County, complex debates and tensions among multiple stakeholders struggle to address local residential development. How can better problem definition benefit rural communities in addressing exurbanization pressures and effects? We asserted that a key factor in the shortcomings of previous solutions was the shortsightedness inherent in policy that attempts to treat individual symptoms without being able to adequately characterize the underlying problem. The goal of the integrative framework is to initiate an iterative process of transparent negotiation, which recognizes a range of potential choices to be considered and to embrace the social complexities that can at times overwhelm scholars and practitioners, inviting simplification and polarization of the issues. This new and emerging framework offers a novel way of approaching conservation and development issues where other frameworks have failed. It helps acknowledge the difficult choices, i.e., trade-offs, that have to be made in a material process like exurbanization. Trade-offs will be necessary in any negotiation related to conservation. Therefore, conflict surrounding specific values, e.g., cultural, financial, or ecological, must be acknowledged upfront to move deeper into issues of plurality. Given the complexity, understanding how the process of exurbanization is being played out within Macon County provided not only an opportunity to demonstrate the functionality of an integrative approach, but also a call for further study of exurbanization dynamics.