Development and assessment of a landscape-scale ecological threat index for the Lower Colorado River Basin

Anthropogenic disturbances impact freshwater biota but are rarely incorporated into conservation planning due to the difficulties in quantifying threats. There is currently no widely accepted method to quantify disturbances, and determining how to measure threats to upstream catchments using disturbance metrics can be time consuming and subjective. We compared four watershed-scale ecological threat indices for the Lower Colorado River Basin (LCRB) using landscape-level threats of land use (e.g., agricultural and urban lands), waterway development and diversions (e.g., number of canals, dams), and human development (e.g., road and railroads density, pollution sites). The LCRB is an ideal region to assess ecological threat indices because of the increasing need for conservation to ensure the persistence of native fishes in highly altered habitat. Each threat was measured for severity (i.e., level of influence on the upstream watershed) and frequency throughout each watershed; both severity and frequency were measured using two different methods. Severity values were based either on peer-reviewed literature and weighted in accordance to their published ecological impact, or assumed equal severity across stressors. Threat frequency was calculated according to either the presence/absence of each stressor, or on the relative density of each stressor in the watershed. Each measure of severity was combined with a measure of frequency, creating four ecological threat indices, and transformed to a 0–100 scale. Threat indices were highly correlated (slopes of 0.94–1.63; R² of 0.82–0.98), and were highest for watersheds close to urban centers, including Phoenix, Tucson, and Flagstaff, Arizona, and Las Vegas, Nevada. Road crossings and density appeared to be the most influential stressors in the index, but the removal of any individual stressor only changed the index by <5.1 units. Our results indicate that a simpler index with less subjectivity (i.e., presence/absence of a stressor in a watershed) provides similar results to the more subjective measure of threats (i.e., peer-reviewed threat severity). Because these threats have been linked to ecological health, the development of the index should be a useful tool to identify regions of greatest potential threat to aquatic biota and can aid in conservation planning for the Lower Colorado River Basin.     

Molecular phylogenetics of Vespoidea indicate paraphyly of the superfamily and novel relationships of its component families and subfamilies

The 24 000+ described species of Vespoidea include many well-known stinging wasps, such as paper wasps and hornets (Vespidae), velvet ants (Mutillidae), spider wasps (Pompilidae) and ants (Formicidae). The compelling behaviours of vespoids have been instrumental in developing theories of stepwise evolutionary transitions, which necessarily depend on an understanding of phylogeny, yet, existing morphological phylogenies for Vespoidea conflict. We collected molecular data from four nuclear genes (elongation factor-1α F2 copy, long-wavelength rhodopsin, wingless and the D2–D3 regions of 28S ribosomal RNA (2700 bp in total)) to produce the first molecular phylogeny of Vespoidea. We analysed molecular data alone and in combination with published morphological data from Brothers and Carpenter. Parsimony analyses left many deeper nodes unsupported, but suggested paraphyly of three families. Total-evidence Bayesian inference produced a more resolved tree, in which the monophyly of Vespoidea was nevertheless ambiguous. Bayesian inference of molecular data alone returned a well-resolved consensus with posterior probabilities of over 95% for most nodes. We used this topology as the best estimate of phylogeny at the family and subfamily levels. Notable departures from previous estimates include: (i) paraphyly of Vespoidea resulting from the nesting of Apoidea within a lineage comprising Formicidae, Scoliidae and two subfamilies of Bradynobaenidae; (ii) paraphyly of Bradynobaenidae, Mutillidae and Tiphiidae; (iii) a sister relationship between Rhopalosomatidae and Vespidae; and (iv) Rhopalosomatidae + Vespidae as sister to all other vespoids/apoids. We discuss character evidence in light of the new phylogeny, and propose a new classification of Aculeata that recognizes eight superfamilies: Apoidea, Chrysidoidea, Formicoidea, Pompiloidea, Scolioidea, Tiphioidea, Thynnoidea and Vespoidea.     

Changes in odor quality discrimination following recovery from olfactory nerve transection

Following recovery from olfactory nerve transection, animals regain their ability to discriminate between odors. Odor discrimination is restored after new neurons establish connections with the olfactory bulb. However, it is not known if the new connections alter odor quality perception. To address this question, 20 adult hamsters were first trained to discriminate between cinnamon and strawberry odors. After reaching criterion (> or = 90% correct response), half of the animals received a bilateral nerve transection (BTX) and half a surgical sham procedure. Animals were not tested again until day 40, a point in recovery when connections are re-established with the bulb. When BTX animals were tested without food reinforcement, they could not perform the odor discrimination task. Sham animals, however, could discriminate, demonstrating that the behavioral response had not been extinguished during the 40 day period. When reinforcement was resumed, BTX animals were able to discriminate between cinnamon and strawberry after four test sessions. In addition, their ability to discriminate between these two familiar odors was no different than that of BTX and sham animals tested with two novel odors, baby powder and coffee. These findings suggest that, after recovery from nerve transection, there are alterations in sensory perception and that restoration of odor quality discrimination requires that the animal must again learn to associate individual odor sensations with a behavioral response.      

The linear theory of neuron networks: The static problem

The construction of a theory of activity in neuron networks of arbitrary topological structure is commenced under the linear excitation hypothesis: we consider conditions for possible steady-state equilibria, deferring a dynamical treatment to the sequel.     

A statistical consequence of the logical calculus of nervous nets

A formal method is derived for converting logical relations among the actions of neurons in a net into statistical relations among the frequencies of their impulses.