Projected changes in elevational distribution and flight performance of montane Neotropical hummingbirds in response to climate change

The hovering flight of hummingbirds is one of the most energetically demanding forms of animal locomotion and is influenced by both atmospheric oxygen availability and air density. Montane Neotropical hummingbirds are expected to shift altitudinally upwards in response to climate change to track their ancestral climatic regime, which is predicted to influence their flight performance. In this study, we use the climate envelope approach to estimate upward elevational shifts for five Andean hummingbird species under two climate change scenarios. We then use field‐based data on hummingbird flight mechanics to estimate the resulting impact of climate change on aerodynamic performance in hovering flight. Our results show that in addition to significant habitat loss and fragmentation, projected upwards elevational shifts vary between 300 and 700 m, depending on climate change scenario and original mean elevation of the target species. Biomechanical analysis indicates that such upwards elevational shifts would yield a～2–5° increase in wing stroke amplitude with no substantial effect on wingbeat frequency. Overall, the physiological impact of elevational shifts of <1000 m in response to climate change is likely to be small relative to other factors such as habitat loss, changes in floristic composition, and increased interspecific competition.     

Maintenance costs of serotiny do not explain weak serotiny

Considerable variation in the duration of serotiny exists among species of both Australian and South African Proteaceae. ‘Weak’ serotiny (pre‐fire loss after <3 years) could be dictated by the costs (water or carbon) of cone/fruit retention or by benefits accruing from pre‐fire seed establishment. We determined that cones/fruits of a range of Australian and south western Cape Proteaceae species (Leucadendron xanthoconus, Aulax umbellata, L. linifolium, L. gandogeri, Hakea drupacea, H. sericea) are not sealed dead wood, but that they continuously lose H₂O and CO₂. Water loss from cones/fruits was poorly controlled, occurring in both light and dark. The rates of both H₂O and CO₂ loss from mature cones/fruits were negatively correlated with the degree of serotiny (r² = 0.59 and 0.18, respectively, P < 0.001 both). However, the amounts of H₂O and CO₂ lost per weight were small relative to the fluxes from leaves (13–29% for H₂O and 3–10% for CO₂). The [N] and [P] in the cones/fruits and seeds was substantial. Despite 25% of N and 38% of P being recovered from the cones/fruits following maturation, the loss of the cones/fruits and seeds would still incur a substantial nutrient cost. The seed [P] was positively correlated with the degree of serotiny (r² = 0.24, P = 0.001). We suggest that maintenance costs (water and carbon) of serotiny, although exceeding those of soil stored seeds, are relatively low. The correlation between the degree of serotiny and seed [P] indicates that stronger serotiny is required, much like sclerophylly, for survival under low nutrient availability in frequently burnt vegetation.     

Habitat variation,mutualism and predation shape the spatio‐temporal dynamics of tansy aphids

1. Spatially distributed resources can lead to the formation of metapopulations, where individual subpopulations are often small and can experience frequent local extinction events followed by recolonisation. An example of terrestrial metapopulations are specialised phytophagous insects on their patchily distributed host plants. 2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small‐scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered. 3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within‐field dispersal determined the spatio‐temporal distribution of aphid colonies. 4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation. 5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio‐temporal dynamics of tansy aphids, particularly in a small‐scale field site.     

Chloroplast DNA‐based studies in molecular ecology may be compromised by nuclear‐encoded plastid sequence

Ongoing genetic transfer from mitochondria and plastids into the nucleus is a well‐documented fact. While in metazoan molecular ecology the need for surveillance against pseudogene‐mediated artefacts when analysing mtDNA sequences is commonly accepted, no comparable measurements have been established for plastid‐based studies. We highlight the impact and management of nuclear mitochondrial insertions, argue that nuclear plastid sequences represent an underestimated but major factor in plant molecular ecology, and discuss potential avenues of remedy in chloroplast studies.     

Night-time sun-compass behaviour of honey bees at the equator

ABSTRACT. In accordance with the peculiarities of the sun's azimuthal path near the equator, African honey bees observed in their night-time dances apparently allowed for the azimuth moving backwards at night relative to its day-time movement. In several cases the bees evidently inferred the actual azimuthal position of the sun, rather than the one that would result from extrapolating a uniform movement of the sun.     

Metabolic conditions in Chlorella

1. The effect of nitrate reduction and assimilation on the CO(2)/O(2) quotient of gas exchange has been used as an index of the relative rates of carbon and nitrogen assimilation in Chlorella pyrenoidosa. Changes in over-all metabolism induced by starvation, high light intensity, and nitrogen deficiency have been studied in comparison with the metabolism of cells growing at light-limiting intensities. 2. Starvation, which results in depletion of carbohydrate reserves, gives rise to a high CO(2)/O(2) quotient ( approximately 0.9) during photosynthesis and, therefore, a high C/N assimilation ratio. Starved cells apparently restore their normal C/N ratio before becoming growing cells. 3. Under photosynthesis-saturating light intensities cells show the high CO(2)/O(2) quotient (0.9) indicative of a high C/N assimilation ratio. Return to low light intensities is followed by the abnormally low CO(2)/O(2) quotient ( approximately 0.4) of a low C/N assimilation ratio. High light intensity apparently gives rise to a condition of a limiting rate of nitrogen assimilation and to an overflow metabolism analogous to that found in other microorganisms. 4. Nitrogen deficiency leads to a completely carbohydrate metabolism in short time experiments and makes still more pronounced the effects characteristic of high light intensity alone. 5. Considerations of nutritional economy sustain the experimental evidence in establishing the metabolism of cells growing under light-limiting intensities as the normal or reference metabolic condition in Chlorella.     

Aspects of Nutrition and the Metabolism of Copper in Isopods

Terrestrial immigrants from the sea have to cope with two importantnutritional problems: a shift in pathways of absorption, andthe altered availability of nutrients. The more terrestrialspecies of littoral crustaceans switch to food as the main sourceof water and salts. No serious difficulties accompany the oraluptake of mobile ions, but the vegetarians amongst the immigrantsare required to assume a new attitude with regard to the assimilationor heavier metals. Some important heavy elements, notably Cuand Zn, are soluble in sea water but form rather intractableorganic complexes in plant tissues. Herbivorous amphipods andisopods on land are incapable of extracting copper directlyfrom their primary food sources. To compensate for this shortcoming,help is enlisted from microorganisms, which render the copperpresent in ill-digested fecal material available to the crustaceans.Moreover, in terrestrial and intertidal herbivorous crustaceans—ascompared with their marine relatives—the storage capacityof the hepatopancreas, as well as the efficiency of Cu-assimilation,is augmented; compartmentalization of Cu-storage is more rigorouslycarried through; the movements of Cu and Zn within the bodyare more strictly regulated, copper, for example, being exchangedbetween different compartments in the course of endogenouslyor exogenously induced phases of the animal's life cycle.