The search for general properties in the structure of ecological networks is currently a very active area of research. Meta‐analyses of published networks are a widely used technique. To have the best chance of discovering common properties though, networks should be constructed using a standardized approach. However, this is rarely the case, and pollination networks are constructed using two main methods: transects and timed observations. To investigate the potential for variation in network structure arising from different construction techniques we constructed plant–pollinator networks using two different methods at a single site, repeating our protocol over three field seasons. Transects and timed observation methods differ in the evenness of observation effort allocated among plant species in the observed community. We show that the uneven allocation of observation effort significantly affects the number of unique interactions in the network, and we reveal a strong trend in effects on web asymmetry and evenness of marginal abundance distributions. However, these effects do not appear to extend to the higher‐order properties of connectance and nestedness.
Objective: The purpose of this article is to present and expand on current theories and measurement techniques for assessing team workload.Background: To date, little research has been conducted on the workload experienced by teams. A validated theory describing team workload, which includes an account of its relation to individual workload, has not been articulated.Method: The authors review several theoretical approaches to team workload. Within the team research literature, attempts to evaluate team workload have typically relied on measures of individual workload. This assumes that such measures retain their validity at the team level of measurement, but empirical research suggests that this method may lack sensitivity to the drivers of team workload.Results: On the basis of these reviews, the authors advance suggestions concerning a comprehensive theory of team workload and methods for assessing it in team settings. The approaches reviewed include subjective, performance, physiological, and strategy shift measures. Theoretical and statistical difficulties associated with aggregating individual-level workload responses to a team-level measure are discussed.Conclusion: Conception and measurement of team workload have not significantly matured alongside developments in individual workload.Application: Team workload remains a complex research area without simple measurement solutions, but as a research domain it remains open for contributions from interested and enterprising researchers.
Avian vision is highly developed, with bird retinas containing rod and double-cone photoreceptors, plus four classes of single cones subserving tetrachromatic colour vision. Cones contain an oil droplet, rich in carotenoid pigments (except VS/ultraviolet-sensitive cones), that acts as a filter, substantially modifying light detected by the photoreceptor. Using dietary manipulations, we tested the effects of carotenoid availability on oil droplet absorbance properties in two species: Platycercus elegans and Taeniopygia guttata. Using microspectrophotometry, we determined whether manipulations affected oil droplet carotenoid concentration and whether changes would alter colour discrimination ability. In both species, increases in carotenoid concentration were found in carotenoid-supplemented birds, but only in the double cones. Magnitudes of effects of manipulations were often dependent on retinal location. The study provides, to our knowledge, the first experimental evidence of dietary intake over a short time period affecting carotenoid concentration of retinal oil droplets. Moreover, the allocation of carotenoids to the retina by both species is such that the change potentially preserves the spectral tuning of colour vision. Our study generates new insights into retinal regulation of carotenoid concentration of oil droplets, an area about which very little is known, with implications for our understanding of trade-offs in carotenoid allocation in birds.
Long-term exposure to ultraviolet (UV) light generates substantial damage, and in mammals, visual sensitivity to UV is restricted to short-lived diurnal rodents and certain marsupials. In humans, the cornea and lens absorb all UV-A and most of the terrestrial UV-B radiation, preventing the reactive and damaging shorter wavelengths from reaching the retina. This is not the case in certain species of long-lived diurnal birds, which possess UV-sensitive (UVS) visual pigments, maximally sensitive below 400 nm. The Order Psittaciformes contains some of the longest lived bird species, and the two species examined so far have been shown to possess UVS pigments. The objective of this study was to investigate the prevalence of UVS pigments across long-lived parrots, macaws and cockatoos, and therefore assess whether they need to cope with the accumulated effects of exposure to UV-A and UV-B over a long period of time. Sequences from the SWS1 opsin gene revealed that all 14 species investigated possess a key substitution that has been shown to determine a UVS pigment. Furthermore, in vitro regeneration data, and lens transparency, corroborate the molecular findings of UV sensitivity. Our findings thus support the claim that the Psittaciformes are the only avian Order in which UVS pigments are ubiquitous, and indicate that these long-lived birds have UV sensitivity, despite the risks of photodamage.
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