Variability and stochasticity of meal size and feeding frequency in the Little Sheanvater Puffinus assimilis

The pattern of chick feeding in Little Shearwater Puffinus assimilis on Selvagem Grande was examined by weighing chicks at 4–h intervals throughout eight successive nights and daily for a further 11 days (19 days in all). Individual meals fed to chicks averaged 23.2 g (s.d. ±4.7) or 13.6% of adult mass. Mass increments over 24 h (NET) were linearly related to the sum of positive mass increments over 4–h intervals during the night (SUM) by the equation NET = 0.36SUM - 5.89 (r²= 0.60). Using this relationship, I estimated that over a period of 18 nights, a mean of 95% of chicks were fed each night, and the mean interval between feeds was 1.05 nights, with a maximum of three nights. There was no significant day-to-day variation in feeding rate. These results were not compatible with the prevalent idea that the purpose of large fat deposits in Procellariiformes is to tide chicks over periodic fasts resulting from poor feeding conditions. On average, chicks required 16 g of food per day to maintain constant mass and converted 33% of their intake of food above this requirement into biomass. Meal size and feeding frequency were independent of chick size and body condition (body-mass corrected for body-size), and the masses of food received by individual chicks each night varied in direct proportion to previous values. These results suggest that the rate of food supply to chicks was not regulated by adjustment according to chicks' nutritional requirements. To some extent, this supports the hypothesis that lipid accumulation among Procellariiformes is related to stochastic variation in food supply rate, resulting from an absence of regulation of feeding. However, feeding was not stochastic, in that adults tended to deliver consistent amounts of food to their chicks, and the pattern of feeding among even the worst-fed chicks was inconsistent with a need for large lipid stores based upon chance variation in food delivery.     

Nutrient enrichment effects on biofilm metabolism in a Mediterranean stream

1. Biofilm biomass and metabolism were analysed in La Solana, a calcareous, undisturbed second-order stream. Measurements were carried out in two Mediterranean climatic extremes, summer and winter. Two on-site experimental channels were used to study changes following nutrient addition to one of them. 2. Algal biomass (chlorophyll a), NDPP (net daily primary production), GDPP (gross daily primary production) and R (respiration) increased in the enriched channel, and these increases were greater in summer. 3. Photosynthetic capacity (Pmax^chl) decreased during summer, possibly due to enhanced self-shading accompanying the increase in biomass. 4. In winter, Pmax^chl increased and reached values similar to those in the summer control channel. Because grazing was low, the higher values of Pmax^chl were attributed to partial substitution of the cyanobacterial assemblage by a green-algae dominated assemblage with higher photosynthetic capacity as well as the low increase in biomass preventing any significant self-shading.     

Predictive Model of Habitat Suitability for the Marbled Murrelet in Western Washington

Abstract: The marbled murrelet (Brachyramphus marmoratus) is a small Pacific seabird with a breeding range that extends from the Aleutian Islands to central California. Throughout most of its breeding range, it uses mature and old-growth coniferous forests as nesting habitat. Although most murrelets seem to nest within 60 km of the coast, occupied nesting habitat has been identified as far as 84 km from the ocean in Washington state. Due to the extensive inland distances within which birds are known to breed, the area requiring surveys to identify breeding sites can be enormous. Therefore, the standard 2-year survey protocol can be expensive and time-consuming for forest management agencies and companies to administer. We developed a logistic regression model to determine whether a suite of forest structural characteristics could be used to reliably predict occupancy of a forest patch by marbled murrelets. We tested the performance of the final model using cross-validation procedures and a sample of independent sites. We used 50 sites surveyed for marbled murrelets to estimate the model, and 48 independent sites were available to test model performance. All 50 sites were on private forestland owned by Rayonier located in the western lowlands of Olympic Peninsula within the Sitka spruce and western hemlock transition zones. We sampled forest habitat at each site, and we collected information on 15 explanatory variables. The best-fitting logistic regression model contained variables that measured number of canopy layers (P<0.001, approx. F test) and mistletoe (Arceuthobium sp.) abundance (P = 0.031, approx. F test). The model misclassified 2 of 33 (94% correct) unoccupied sites as occupied using a classification cut-off (c) of c=0.25. In the other direction, under cross-validation the final model misclassified 2 of 17 (88% correct) occupied sites as unoccupied. On a test of the model against an independent sample, using a classification cut-off value of c = 0.25, the final model correctly classified 36 of 48 sites (75% correct). The final model misclassified 3 of 31 occupied sites as unoccupied (90% correct). Use of predictive models could greatly reduce the amount of forest that requires surveys by screening out those sites with little probability of use and by focusing remaining effort on higher probability sites, resulting in a higher likelihood of identifying occupied sites and thereby more efficiently conserving marbled murrelet nesting habitat.     

Evolutionary and ecological implications of genome size in the North American endemic sagebrushes and allies (Artemisia, Asteraceae)

The genome size of 51 populations of 20 species of the North American endemic sagebrushes (subgenus Tridentatae ), related species, and some hybrid taxa were assessed by flow cytometry, and were analysed in a phylogenetic framework. Results were similar for most Tridentatae species, with the exception of three taxonomically conflictive species:  Artemisia bigelovii Gray,  Artemisia pygmaea Gray, and  Artemisia rigida Gray. Genome size homogeneity (together with the high morphological, chemical, and karyological affinities, as well as low DNA sequence divergence) could support a recent diversification process in this geographically restricted group, thought to be built upon a reticulate evolutionary framework. The Tridentatae and the other North American endemic Artemisia show a significantly higher genome size compared with the other subgenera. Our comparative analyses including genome size results, together with different kinds of ecological and morphological traits, suggest an evolutionary change in lifestyle strategy linked to genome expansion, in which junk or selfish DNA accumulation might be involved. Conversely, weed or invasive behaviour in Artemisia is coupled with lower genome sizes. Data for both homoploid and polyploid hybrids were also assessed. Genome sizes are close to the expected mean of parental species for homoploid hybrids, but are lower than expected in the allopolyploids, a phenomenon previously documented to be related with polyploidy.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 631–649.     

Growth and provisioning strategies of Northern Fulmars Fulmarus glacialis

Growth and foraging strategies in procellariiforms show a great deal of variation, but the fulmarine petrels are notable in that chicks are fed frequently and develop unusually rapidly. This study examined age-related and daily variation in provisioning of the Northern Fulmar Fulmarus glacialis throughout the chick-rearing period at Fair Isle in 1997. In common with many other petrels, meal mass showed an initial rise with age, probably because of a gradual increase in chick gut capacity, but then levelled off. By comparison, feeding frequency showed little age-specific variation until chicks reached the oldest age-class, when the number of meals declined to less than a third of the previous level as chicks underwent mass recession prior to fledging. Compared with the limited day-to-day variation in mean provisioning rates for the whole sample, food delivery to particular chicks was much more variable, suggesting that differences in feeding rates were determined by stochastic factors influencing the feeding success of individual parents. The caloric density of feeds and their size in relation to adult mass were lower in Northern Fulmars than in most other Procellariiformes. This implies that adults are not heavily dependent on stomach oil formation to raise the energy content of the payload, but rely on a high feeding frequency to maintain adequate rates of energy transfer to chicks.