Fire,flow and dynamic equilibrium in stream macroinvertebrate communities

1. The complex effects of disturbances on ecological communities can be further complicated by subsequent perturbations within an ecosystem. We investigated how wildfire interacts with annual variations in peak streamflow to affect the stability of stream macroinvertebrate communities in a central Idaho wilderness, USA. We conducted a 4‐year retrospective analysis of unburned (n = 7) and burned (n = 6) catchments, using changes in reflectance values (Δ NBR) from satellite imagery to quantify the percentage of each catchment’s riparian and upland vegetation that burned at high and low severity. 2. For this wildland fire complex, increasing riparian burn severity and extent were associated with greater year‐to‐year variation, rather than a perennial increase, in sediment loads, organic debris, large woody debris (LWD) and undercut bank structure. Temporal changes in these variables were correlated with yearly peak flow in burned catchments but not in unburned reference catchments, indicating that an interaction between fire and flow can result in decreased habitat stability in burned catchments. 3. Streams in more severely burned catchments exhibited increasingly dynamic macroinvertebrate communities and did not show increased similarity to reference streams over time. Annual variability in macroinvertebrates was attributed, predominantly, to the changing influence of sediment, LWD, riparian cover and organic debris, as quantities of these habitat components fluctuated annually depending on burn severity and annual peak streamflows. 4. These analyses suggest that interactions among fire, flow and stream habitat may increase inter‐annual habitat variability and macroinvertebrate community dynamics for a duration approaching the length of the historic fire return interval of the study area.     

Gametogenesis,brooding and planulation in laboratory populations of a temperate scleractinian coral Balanophyllia elegans maintained under contrasting photoperiod regimes

Summary

Males of Balanophyllia elegans Verrill, 1864 in Monterey Bay, California, spawn in the fall. Fertilization occurs within the females and the internally brooded embryos develop into large benthic planulae that are released mainly in the late winter. Field-collected corals were held in the laboratory under contrasting photoperiod regimes (ambient or in-phase, and 6 months out-of-phase) for 6.5 years. After two years in the laboratory corals planulated at the same time, independent of photoperiod. Corals show a cyclic pattern of later winter and early spring planulation that coincides with declining sea temperatures in Monterey Bay. Gametes appeared in the first laboratory generation at IS months and brooded embryos were found in females at 31 months under both light regimes. Planulae production by laboratory-reared corals peaked at the same time as that of the parents. These findings suggest that the temporal pattern of planulation is regulated by both endogenous and exogenous components that can be modified in some way by disturbance caused to the corals when collected or by the time of collection.     

Postfledging Survival and Development of Juvenile Lilac-Crowned Parrots

Abstract: We fitted radiotransmitters to 68 lilac-crowned parrot (Amazona finschi) fledglings from 1996 to 2003 to determine the survival and development of juveniles during their first year after leaving the nest. Overall, first-year survival was 73% (CI = 53–94%) and all mortalities occurred within 5 weeks of fledging, with highest mortality in the first week postfledging. Survival varied between years, influencing recruitment of independent young in the population. Nesting lilac-crowned parrots produced 0.70 independent young per egg-laying pair during 1996–2003. Lowest productivity of 0.25 independent young per pair occurred in 2003, with 40% postfledging survival. Juvenile development after fledging was characterized by variations in mobility, distance from the nest, and separation distance between siblings. Mobility and distance of young birds from the nest increased linearly with months postfledging. The first 2–3 weeks after fledging were characterized by low mobility and survival of young parrots, making this the most critical phase postfledging. The dependency period for young parrots extended to 4–5 months postfledging and was characterized by increased mobility and low separation between siblings, as juveniles traveled in family groups. Independence occurred in month 5 and was marked by a significant increase in mobility and separation between siblings, indicating the break-up of family groups. The first weeks after leaving the nest were crucial for survival and highlight the need for secure habitats where fledglings can improve flight and locomotory skills. The 4–5-month dependency of young parrots may be a key period for development, enhancing survival, and establishment in the breeding population. Release programs need to replicate learning and development acquired during the postfledging dependency phase to enhance survival of captive-reared psittacines. Researchers should conduct surveys of parrot group sizes during the dependency period 1–4 months after the end of nesting to provide reliable demographic data on annual recruitment of wild populations.     

Changes in the Nucleus and the Endoplasmic Reticulum during Differentiation of a Sieve Element in Mimosa pudica L.

The differentiating sieve element in stem and leaf phloem ofMimosa pudica L. was examined with the electron microscope.The nucleus of a sieve element at first resembles that of acompanion cell, except that its nucleolus is smaller. The firstindication of approaching disintegration is a change in theappearance of the nuclear envelope. With the fixatives used,its profile becomes wider and clearer, giving the impressionof having been dilated. Subsequently, the nuclear contents disintegrateand the envelope breaks apart. No nuclear remnants are discerniblein mature sieve elements. The endoplasmic reticulum (ER) ofyoung sieve elements consists of cisternae-bearing ribosomes.At the beginning of nuclear disintegration ER cisternae becomestacked, with electron-dense material accumulating between thecisternae. The stacking assumes various forms. Some of the stackedER is independent of cell organelles and occurs next to theplasmalemma along the cell wall. Part of the ER becomes stackedagainst the plastids or the nucleus. There is also unstackedER which forms an anastomosing system along the plasmalemma.All of the modified ER bears no ribosomes. The anastomosingER appears to persist longer than the stacked ER.     

Validity of the bereavement exclusion criterion for the diagnosis of major depressive episode

Since the publication of DSM-III in 1980, the official position of American psychiatry has been that the presence of bereavement is an exclusion criterion for the diagnosis of a major depressive episode (MDE). However, the empirical validity of this exclusion has not been well established. As DSM-V is now being planned, it is timely to reexamine the bereavement exclusion, particularly in the light of new evidence since the last reviews of this subject. This paper evaluates the relative validity of two competing hypotheses: 1) the bereavement exclusion for the diagnosis of MDE is not valid because, using validating criteria, bereavement related depression (BRD) within the first two months after the death of a loved one resembles non-bereavement related depression (SMD); 2) the bereavement exclusion for the diagnosis of MDD is valid because, using validating criteria, BRD within the first two months after the death of a loved one does not resemble SMD. The prevailing evidence more strongly supports Hypothesis 1 than Hypothesis 2. Thus, the bereavement exclusion for the diagnosis of MDE may no longer be justified.     

Short-term variation in the isotopic composition of organic matter allocated from the leaves to the stem of Pinus sylvestris: effects of photosynthetic and postphotosynthetic carbon isotope fractionation

We aimed to quantify the separate effects of photosynthetic and postphotosynthetic carbon isotope discrimination on δ¹³C of the fast‐turn‐over carbon pool (water soluble organic carbon and CO₂ emitted from heterotrophic tissues), including their diel variation, along the pathway of carbon transport from the foliage to the base of the stem. For that purpose, we determined δ¹³C in total and water‐soluble organic matter of the foliage plus δ¹³C and δ¹⁸O in phloem organic matter of twigs and at three heights along the stem of Pinus sylvestris over a nine‐day period, including four measurements per day. These data were related to meteorological and photosynthesis parameters and to the δ¹³C of stem‐emitted CO₂. In the canopy (foliage and twigs), the δ¹³C of soluble organic matter varied diurnally with amplitudes of up to 1.9‰. The greatest ¹³C enrichment was recorded during the night/early morning, indicating a strong influence of starch storage and remobilization on the carbon isotope signatures of sugars exported from the leaves. ¹³C enrichment of soluble organic matter from the leaves to the twig phloem and further on to the phloem of the stem was supposed to be a result of carbon isotope fractionation associated with metabolic processes in the source and sink tissues. CO₂ emitted from the stem was enriched by 2.3–5.2‰ compared with phloem organic matter. When day‐to‐day variation was addressed, water‐soluble leaf δ¹³C and twig phloem δ¹⁸O were strongly influenced by c_i/c_a and stomatal conductance (G_s), respectively. These results show that both photosynthetic and postphotosynthetic carbon isotope fractionation influence δ¹³C of organic matter over time, and over the length of the basipetal transport pathway. Clearly, these influences on the δ¹³C of respired CO₂ must be considered when using the latter for partitioning of ecosystem CO₂ fluxes or when the assessment of δ¹³C in organic matter is applied to estimate environmental effects in c_i/c_a.