Moist-Soil Seed Abundance in Managed Wetlands in the Mississippi Alluvial Valley

Abstract: Managed moist-soil units support early succession herbaceous vegetation that produces seeds, tubers, and other plant parts used by waterfowl in the Mississippi Alluvial Valley (MAV), USA. We conducted a stratified multi-stage sample survey on state and federal lands in the MAV of Arkansas, Louisiana, Mississippi, and Missouri during autumns 2002–2004 to generate a contemporary estimate of combined dry mass of seeds and tubers (herein seed abundance) in managed moist-soil units for use by the Lower Mississippi Valley Joint Venture (LMVJV) of the North American Waterfowl Management Plan. We also examined variation in mean seed abundance among moist-soil units in 2003 and 2004 in relation to management intensity (active or passive), soil pH and nutrient levels, proportional occurrence of plant life-forms (e.g., grass, flatsedge, and forb; vine; woody plants), and unit area. Estimates of mean seed abundance were similar in 2002 (x̄ = 537.1 kg/ha, SE = 100.1) and 2004 (x̄ = 555.2 kg/ha, SE = 105.2) but 35–40% less in 2003 (x̄ = 396.8 kg/ha, SE = 116.1). Averaged over years, seed abundance was 496.3 kg/ha (SE = 62.0; CV = 12.5%). Multiple regression analysis indicated seed abundance varied among moist-soil units inversely with proportional occurrence of woody vegetation and unit area and was greater in actively than passively managed units (R²_adj = 0.37). Species of early succession grasses occurred more frequently in actively than passively managed units (P ≤ 0.09), whereas mid- and late-succession plants occurred more often in passively managed units (P ≤ 0.02). We recommend the LMVJV consider 556 kg/ha as a measure of seed abundance for use in estimating carrying capacity in managed moist-soil units on public lands in the MAV. We recommend active management of moist-soil units to achieve maximum potential seed production and further research to determine recovery rates of seeds of various sizes from core samples and the relationship between seed abundance and unit area. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):707–714; 2008)     

Experimental Studies of the Factors Controlling Transpiration: II. THE RELATION BETWEEN TRANSPIRATION RATE AND LEAF WATER CONTENT

Data are presented which show, when stomatal control is eliminated,that wheat leaves may lose 5–6 per cent. and Pelargoniumleaves 10–12 per cent. of their water without any reductionin the transpiration rate. Experiments in which Pelargonium and wheat leaves, with stomatalcontrol present, were submitted to cycles of changing watercontent also failed to establish any direct relation betweentranspiration rate and leaf water content. It is concluded that leaf water content over the range of 70–100per cent. of that present in the turgid state has no significanteffect in determining the rate of water loss from leaves. A repetition of Knight's experiment showed that stomata openedin still air and closed in moving air. This was not recordedby Knight, who used a porometer cup permanently attached tothe leaf. It is concluded that the higher transpiration raterecorded by Knight after a period of still air was due to widerstomatal aperture and not to the higher leaf water content assuggested by him.     

Biochemical and ecological characterization of two peroxidase isoenzymes from the mangrove, Rhizophora mangle

This study examines phenolic peroxidase (POX) in Rhizophora mangle L. leaves in order to assess its role in phenolic manipulation and H₂O₂ scavenging. Sun-exposed and understorey leaves experiencing varying degrees of nutrient stress were analysed from an oligotrophic cay off the coast of Belize. POX activity was unaffected by growth environment, but increased throughout leaf development and persisted through senescence and after abscission. Histochemical analyses indicated POX activity throughout leaf tissues, especially in the apoplast. Phenolics were similarly broadly distributed. Two isoenzymes of POX were partially characterized with pIs of 4.1 and 6.3 and masses of 65.5 and 54.3 kDa, respectively. The larger, more acidic isoenzyme showed especially high heat stability, showing no reduced activity after 24 h at 60 °C. Rhizophora mangle POX oxidized quercetin preferentially, and, to a lesser extent, coniferyl alcohol, caffeic acid, chlorogenic acid, and p-coumaric acid. It did not oxidize ascorbate, but ascorbate could act as a secondary electron donor in the presence of a phenolic substrate and H₂O₂. However, because quercetin and other aglycones were not present in R. mangle leaves, and because POX showed no activity with the most abundant leaf flavonoid, rutin, it was concluded that detoxification of H₂O₂ is secondary to the other roles of POX in manipulation of phenolics.     

Estimation and Correction of Visibility Bias in Aerial Surveys of Wintering Ducks

Abstract: Incomplete detection of all individuals leading to negative bias in abundance estimates is a pervasive source of error in aerial surveys of wildlife, and correcting that bias is a critical step in improving surveys. We conducted experiments using duck decoys as surrogates for live ducks to estimate bias associated with surveys of wintering ducks in Mississippi, USA. We found detection of decoy groups was related to wetland cover type (open vs. forested), group size (1–100 decoys), and interaction of these variables. Observers who detected decoy groups reported counts that averaged 78% of the decoys actually present, and this counting bias was not influenced by either covariate cited above. We integrated this sightability model into estimation procedures for our sample surveys with weight adjustments derived from probabilities of group detection (estimated by logistic regression) and count bias. To estimate variances of abundance estimates, we used bootstrap resampling of transects included in aerial surveys and data from the bias-correction experiment. When we implemented bias correction procedures on data from a field survey conducted in January 2004, we found bias-corrected estimates of abundance increased 36–42%, and associated standard errors increased 38–55%, depending on species or group estimated. We deemed our method successful for integrating correction of visibility bias in an existing sample survey design for wintering ducks in Mississippi, and we believe this procedure could be implemented in a variety of sampling problems for other locations and species. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):808–813; 2008)     

Prodigies of propagation: the many modes of clonal replication in boloceroidid sea anemones (Cnidaria,Anthozoa, Actiniaria)

Summary

Diverse modes of clonal propagation were documented in tiny zooxanthellate sea anemones from the tropical Pacific. All were boloceroidids, as indicated by the tentacles' basal sphincter and the animals' swimming behavior. In one species, single tentacles were pinched off at the sphincter, shed into the coelenteron, and brooded there while regenerating into minute new polyps in ~4 days. Within a day of release, the propagules fed on live prey and swam by lashing the tentacles. A similar process occurs in another species studied, Bunodeopsis medusoides. In a third species a previously undescribed mode of replication was seen. These anemones bore a primary cycle of tentacles that engaged actively in feeding and swimming, were not shed, and showed no sign of producing polyps. Alternating with these tentacles were fan-like clusters of shorter tentacles that were relatively inactive in feeding and swimming. Despite the sphincter at the base of each of these clustered tentacles, they were never shed singly; instead, each cluster separated as a unit that then regenerated into a new polyp. Two other replicative modes were observed in similar, minute boloceroidid anemones collected together in the same habitat: longitudinal fission, not previously reported in boloceroidids, and pedal scission. Modes of replication in these actinians are more diverse than once thought, but the selective forces behind this variation are so far unexplored. These prolific anemones may regularly be taking advantage of their combination of swimming and regenerative abilities to achieve dispersal, not only by sexually produced larvae, but also by cloned polyps.     

Conserving Waste Rice for Wintering Waterfowl in the Mississippi Alluvial Valley

Abstract: Rice lost before or during harvest operations (hereafter waste rice) provides important food for waterfowl in the Mississippi Alluvial Valley, USA, but >70% of waste rice is lost during autumn. We conducted experiments in 19 production rice fields in Arkansas and Mississippi during autumns 2003 and 2004 to evaluate the ability of common postharvest practices (i.e., burn, mow, roll, disk, or standing stubble) to conserve waste rice. We detected a postharvest treatment effect and a positive effect of initial abundance of waste rice on late-autumn abundance of waste rice (P ≤ 0.022). Standing stubble contained the greatest abundance of waste rice followed by burned, mowed, rolled, and disked stubble. We recommend standing stubble or burning to maximize waste rice abundance for wintering waterfowl.     

Reproduction of Antarctic Benthic Marine Invertebrates: Tempos, Modes, and Timing

Work on the life histories of common antarctic benthic marineinvertebrates over the past several decades demands a revisionof several widely held paradigms. First, contrary to expectationsderived from work on temperate species, there is little or noevidence for temperature adaptation with respect to reproduction(gametogenesis), development, and growth. It remains to be determinedwhether the slow rates of these processes reflect some inherentinability to adapt to low temperatures, or are a response tofeatures of the antarctic marine environment not directly relatedto low temperature, such as low food resources. Secondly, contraryto the widely accepted opinion designated as "Thorson's rule,"pelagic development is common in many groups of shallow-watermarine invertebrates. In fact in some groups, such as asteroids,pelagicdevelopment is as prevalent in McMurdo Sound, the southern-mostopen-water marine environment in the world, as in central California.In other taxonomic groups, especially gastropods, there doesseem to be a genuine trend toward non-pelagic development fromtropical to antarctic latitudes. Although this trend has beenpredicted by theoretical models, its underlying causes appearto be group specific rather than general. Thirdly, pelagic lecithotrophicdevelopment, often considered to be of negligible importance,occurs in many shallow-water antarctic marine macroinvertebrates.Pelagic lecithotrophy may be an adaptation to a combinationof poor food conditions in antarctic waters most of the yearand slow rates of development. Nevertheless, some of the mostabundant and widespread antarctic marine invertebrates havepelagic planktotrophic larvae that take very long times to completedevelopment to metamorphosis. These species areparticularlyprevalent in productive regions of shallow water (<30 m),which are frequently disturbed by anchor ice formation, andthe production of numerous pelagic planktotrophic larvaemayrepresent a strategy for colonization. Although planktotrophiclarvae tend to be seasonal in occurrence, their production isnot linked particularly closely to the mid-summer pulse of phytoplanktonproduction. These larvae show no evidence of starvation, evenduring times when phytoplankton abundance is very low, and theymay depend on unusual sources of food, such as bacteria. Howthey escape the selective conditions that apparently led toa predominance of non-feeding modes of development in antarcticmarine invertebrates remains as a major challenge for antarcticmarine biology.