Speciation and the Latitudinal Diversity Gradient: Insights from the Global Distribution of Endemic Fish.

The nearly universal pattern that species richness increases from the poles to the equator (the latitudinal diversity gradient [LDG]) has been of intense interest since its discovery by early natural-history explorers. Among the many hypotheses proposed to explain the LDG, latitudinal variation in (1) productivity, (2) time and area available for diversification, and (3) speciation and/or extinction rates have recently received the most attention. Because tropical regions are older and were formerly more widespread, these factors are often intertwined, hampering efforts to distinguish their relative contributions to the LDG.

Fitness Consequences of Boldness in Juvenile and Adult Largemouth Bass.

To date, most studies investigating the relationship between personality traits and fitness have focused on a single measure of fitness (such as survival) at a specific life stage. However, many personality traits likely have multiple effects on fitness, potentially operating across different functional contexts and stages of development. Here, we address the fitness consequences of boldness, under seminatural conditions, across life stages and functional contexts in largemouth bass (Micropterus salmoides).

Large-scale biodiversity patterns in freshwater phytoplankton.

Our planet shows striking gradients in the species richness of plants and animals, from high biodiversity in the tropics to low biodiversity in polar and high-mountain regions. Recently, similar patterns have been described for some groups of microorganisms, but the large-scale biogeographical distribution of freshwater phytoplankton diversity is still largely unknown. We examined the species diversity of freshwater phytoplankton sampled from 540 lakes and reservoirs distributed across the continental United States and found strong latitudinal, longitudinal, and altitudinal gradients in phytoplankton biodiversity, demonstrating that microorganisms can show substantial geographic variation in biodiversity.

Resource heterogeneity, soil fertility, and species diversity: effects of clonal species on plant communities.

Spatial heterogeneity in soil resources is widely thought to promote plant species coexistence, and this mechanism figures prominently in resource-ratio models of competition. However, most experimental studies have found that nutrient enhancements depress diversity regardless of whether nutrients are uniformly or heterogeneously applied. This mismatch between theory and empirical pattern is potentially due to an interaction between plant size and the scale of resource heterogeneity.

Recycling‐mediated facilitation and coexistence based on plant size.

We introduce nutrient recycling into a model where competitors differ in the scale at which they perceive their environment. In a two-resource system with both external nutrient inputs and recycling, larger consumers ("integrators") often generate resource distributions that favor their smaller ("nonintegrator") competitors, and vice versa. This occurs because recycling of integrator biomass reduces between-patch resource heterogeneity, whereas recycling of nonintegrator biomass does not.

Perturbations alter community convergence, divergence, and formation of multiple community states.

Environmental perturbations (e.g., disturbance, fertilization) commonly shift communities to a new mean state, but much less is known about their effects on the variability (dispersion) of communities around the mean, particularly when perturbations are combined.

Regional coexistence and local dominance in Chaoborus: species sorting along a predation gradient.

Variation in the intensity of predation across the well-known environmental gradient of freshwater habitats from small, ephemeral ponds to large, permanent lakes is a key factor in the development and maintenance of aquatic community structure. Here, we present data on the distribution and abundance of four species of Chaoborus (Diptera: Chaoboridae) across this environmental gradient. Chaoborus show a distinct pattern of species sorting when aquatic systems are divided into fish and fishless environments, and this pattern is consistent with species traits known to influence their vulnerability to fish predation (i.

Competition among plant species that interact with their environment at different spatial scales.

Clonal plants that are physiologically integrated might perceive and interact with their environment at a coarser resolution than smaller, non-clonal competitors. We develop models to explore the implications of such scale asymmetries when species compete for multiple depletable resources that are heterogeneously distributed in space across two patches. Species are either 'non-integrators', whose growth in each patch depends on resource levels in that patch alone, or 'integrators', whose growth is equal between patches and depends on average resource levels across patches.

Consequences of niche overlap for ecosystem functioning: an experimental test with pond grazers.

While the number of studies investigating the effects of species diversity on ecosystem properties continues to expand, few have explicitly examined how ecosystem functioning depends quantitatively on the degree of niche complementarity among species. We report the results of a microcosm experiment where similarity in habitat use among aquatic snail species was evaluated as a predictor of changes in community and ecosystem properties due to increasing species richness. Replicate microcosms with all possible one- and two-species combinations of a guild of six snail species were stocked with identical initial snail biomass.

Fish reintroductions reveal smooth transitions between lake community states.

Whether communities respond smoothly or discontinuously to changing environmental conditions has important consequences for the preservation and restoration of ecosystems. Theory shows that communities may exhibit a variety of responses to environmental change, including abrupt transitions due to the existence of alternate states. However, there have been few opportunities to look for such transitions in nature.

Interactions between adult and larval bluegill sunfish: positive and negative effects.

Adult fish may affect the growth and survival of conspecific larvae through a variety of pathways, including negative interactions via competition for shared limiting resources or via predation (i.e., cannibalism), and positive interactions due to the consumption of larval predators and via resource enhancement (i.

Variation in resource abundance affects diet and feeding morphology in the pumpkinseed sunfish (Lepomis gibbosus).

The pumpkinseed sunfish (Lepomis gibbosus Linnaeus; Centrarchidae) feeds extensively on molluscs, crushing them between its pharyngeal jaws. To address whether differences in mollusc availability might affect pumpkinseed diet and jaw morphology, we collected pumpkinseed from six Wisconsin lakes that varied in mollusc abundance and diversity. The percentage of molluscs in the diet increased directly with mollusc abundance.

Naloxone does not alter the perception of pain induced by electrical and thermal stimulation of the skin in healthy humans.

It has been hypothesized that, in the absence of acute or chronic pain, a tonically active system exists involving opioid peptides, which ensures a certain level of pain insensitivity. Although various studies have failed to support this concept, it has been reported that in conditions of both experimentally induced and clinical pain, high doses of the opioid antagonist naloxone induced a state of hyperalgesia and thus seemed to set off this hypothetical system. Lower doses were, however, without effect or even acted as analgesics.

Effects of graded oral doses of a new 5-hydroxytryptamine/noradrenaline uptake inhibitor (Ro 15-8081) in comparison with 60 mg codeine and placebo on experimentally induced pain and side effect profile in healthy men.

1. Ro 15-8081 (Hoffmann-La Roche, Basle, Switzerland) is a novel mixed 5-HT/noradrenaline uptake inhibitor producing potent antinociceptive effects in animal pain models. 2.

Effects of oral cisapride on interdigestive jejunal motor activity, psychomotor function, and side-effect profile in healthy man.

Intravenous cisapride was shown to induce a phase-2-like pattern of human interdigestive jejunal motor activity containing an increased number of propagated contractions. This study investigated the effects of oral cisapride in 12 fasting healthy males. Jejunal pressures were recorded by a pneumohydraulic system and five catheter orifices positioned 10-30 cm aborad the ligament of Treitz.

Intravenous cisapride accelerates delayed gastric emptying and increases antral contraction amplitude in patients with primary anorexia nervosa.

Delayed gastric emptying is common in primary anorexia nervosa. We investigated in 12 patients whether gastric emptying could be accelerated by the prokinetic drug cisapride. Patients were studied on two occasions 1 wk apart and received, under random double-blind conditions, 8 mg of cisapride and placebo intravenously.

Effects of cisapride on jejunal motor activity in fasting healthy humans.

The effects of cisapride on jejunal interdigestive motor activity were studied in 12 healthy men participating in three experiments each. Five minutes after an activity front (phase III) they received, in random double-blind fashion, 10 mg of cisapride, 4 mg of cisapride, or saline placebo by intravenous injection. Motor activity was recorded for 4 h.

Experimental pain induced by electrical and thermal stimulation of the skin in healthy man: sensitivity to 75 and 150 mg diclofenac sodium in comparison with 60 mg codeine and placebo.

Models with experimentally induced pain in healthy man might be useful for the screening for analgesic effects of new drugs. Experimental pain models have been shown to discriminate reliably between the effects of opioid analgesics and placebo but their sensitivity to nonsteroidal anti-inflammatory agents is disputed. This study investigated whether it would be possible by using electrically and thermally induced cutaneous pain to discriminate reliably the effects of single oral doses of 75 and 150 mg diclofenac sodium on the one hand and 60 mg codeine on the other from those of placebo.

Experimental studies of seed predation in old-fields.

In a pair of experiments conducted in old-field habitats in southwestern Michigan (USA), we examined rates of seed loss to post-dispersal predators (ants and rodents). Seeds from 4-6 species of "biennial" plants were tested over a range of seed densities and habitat types. We found that seed removal was significantly higher in vegetated habitats than in areas of disturbed soil (both simulated small-animal diggings and a plowed field).