Search

Light and nutrient availability are assumed to largely control the dynamics and trophic efficiency of marine planktonic food webs, and are expected to be influenced by climate change (i.e. changes in stratification due to global warming). During an 8-day mesocosm experiment, we investigated the propagation of light energy up to the copepod trophic level in ultra-oligotrophic Eastern Mediterranean waters. Using mesocosms with light treatments corresponding to ca. 40% (L1) and 4.5% (L4) of the incident light intensity (simulating light conditions at 10 and 50–60 m depths, respectively), we assessed the feeding behaviour of the dominant copepod Clausocalanus furcatus every second day. We hypothesized that increased availability of copepod food at higher light levels would result in increased copepod ingestion rates and selectivity. Our results showed that copepod prey (microbial biomass>5 μm) had only a small increase in the L1 and daily rations (DRs) of C. furcatus were similar among treatments (usually <15% of body carbon). Nevertheless, microplankton was clearly selected in L1, having double the contribution in the DR of C. furcatus compared with L4. A more balanced selective feeding pattern was observed in L4, with nanoplankton also being important in the diet. An increase in the copepod stock in the L1 compared with L4, observed at the end of the experiment, is likely associated with the light-mediated effects on C. furcatus feeding behaviour. We suggest that the importance of light availability on the efficiency of the marine planktonic food web should be further considered by climate change predictive models. [ABSTRACT FROM PUBLISHER]

Several Heliconius L. butterflies species form nocturnal aggregations in sites with a particular architecture. Roosts are usually formed under relatively dense vegetation mats where dry vines or branches provide a perch for the night. These sites may last for months. To understand the importance of factors related to the expression of Heliconius roosting, data on light, temperature, relative humidity, wind, and use of wing color cues were recorded at H. erato and H. sara roost sites in Costa Rica and Panama in 2008 and 2009. The results show that roost sites offer reduced light conditions at dusk, provide a drier environment compared with its vicinity, and offer protection from wind and rain. Moreover, individuals use wing color recognition under reduced light conditions at dusk to successfully assemble aggregations. These findings provide key information for future experiments to study the use of landmarks, hygrosensitivity, and dim-light eye adaptations in Heliconius navigation to find roost sites. [ABSTRACT FROM AUTHOR]

Scaling leaf-level measurements to estimate carbon gain of entire leaf crowns or canopies requires an understanding of the distribution of photosynthetic capacity and corresponding light microenvironments within a crown. We have compared changes in the photosynthetic light response and nitrogen (N) content (per unit leaf area) of Pinus contorta Dougl. ssp. latifolia Engelm. (lodgepole pine) leaves in relation to their age and light microenvironment. The vertical gradient in integrated daily photosynthetic photon flux density (PPFD) from the upper to the lower crown of lodgepole pine was similar in magnitude to the horizontal gradient in daily PPFD along shoots from young to old leaves. The relationship between light-saturated net photosynthesis (Amax) and daily PPFD was significant for both young and old leaves. However, old leaves had a lower Amax than young leaves in a similar daily irradiance regime. For leaves of all ages from throughout the crown, Amax was linearly related to the estimated daily net carbon gain that leaves could achieve in their natural PPFD environment (estimated Aday) (r2 = 0.84, P < 0.001, n = 39), indicating that estimated Aday may be dominated by carbon fixed when leaves are light-saturated and operating at Amax. Comparison of the PPFD required to achieve Amax and the PPFD available to the leaves showed that all of the measured leaves (n = 39), regardless of their position in the crown or age, were in light environments that could light-saturate photosynthesis for a similar proportion of the day. For all data pooled, foliar N was weakly correlated with daily PPFD. Analyzing each leaf age class separately showed that foliar N was significantly related to daily PPFD, Amax, and estimated Aday for the youngest leaves but not for middle-aged or old leaves. Therefore, the general theory that foliar N is allocated within a crown according to total daily light availability was supported only for young (1–4 years old) leaves in this study. [ABSTRACT FROM PUBLISHER]