Changes in Agriculture and Abundance of Snow Geese Affect Carrying Capacity of Sandhill Cranes in Nebraska

ABSTRACT The central Platte River valley (CPRV) in Nebraska, USA, is a key spring-staging area for approximately 80% of the midcontinent population of sandhill cranes (Grus canadensis; hereafter cranes). Evidence that staging cranes acquired less lipid reserves during the 1990s compared to the late 1970s and increases in use of the CPRV by snow geese (Chen caerulescens) prompted us to investigate availability of waste corn and quantify spatial and temporal patterns of crane and waterfowl use of the region. We developed a predictive model to assess impacts of changes in availability of corn and snow goose abundance under past, present, and potential future conditions. Over a hypothetical 60-day staging period, predicted energy demand of cranes and waterfowl increased 87% between the late 1970s and 1998–2007, primarily because peak abundances of snow geese increased by 650,000 and cranes by 110,000. Compared to spring 1979, corn available when cranes arrived was 20% less in 1998 and 68% less in 1999; consequently, the area of cornfields required to meet crane needs increased from 14,464 ha in 1979 to 32,751 ha in 1998 and 90,559 ha in 1999. Using a pooled estimate of 88 kg/ha from springs 1998–1999 and 2005–2007, the area of cornfields needed to supply food requirements of cranes and waterfowl increased to 65,587 ha and was greatest in the eastern region of the CPRV, where an estimated 54% of cranes, 47% of Canada geese (Branta canadensis), 45% of greater white-fronted geese (Anser albifrons), and 46% of snow geese occurred during ground surveys. We estimated that a future reduction of 25% in available corn or cornfields would increase daily foraging flight distances of cranes by 27–38%. Crane use and ability of cranes to store lipid reserves in the CPRV could be reduced substantially if flight distance required to locate adequate corn exceeded a physiological maximum distance cranes could fly in search of food. Options to increase carrying capacity for cranes include increasing accessibility of cornfields by restoring degraded river channels to disperse roosting cranes and increasing wetland availability in the Rainwater Basin to attract snow geese using the CPRV.     

Experimental Studies of the Factors Controlling Transpiration: I. APPARATUS AND EXPERIMENTAL TECHNIQUE

Apparatus and experimental techniques are discussed for usein the investigation of transpiration rate of leaves as controlledby stomatal aperture and leaf water content. The leaf chambers used and the methods adopted for the estimationof the water transpired are described. The designs of the porometer cups used for the different typesof leaves (Pelargonium and wheat) employed in the work are described.To obviate the difficulty that stomata within the cup behaveabnormally, the design employed makes possible a removal ofthe cup from the leaf except during the short periods requiredto estimate stomatal resistance to air flow at intervals duringthe course of an experiment. In these experiments the water content of the leaf is changedat will by interrupting the water-supply and re-establishingit to permit recovery from wilting. The methods used to carryout this cycle of operations are fully dealt with. Determinationsof the transpiration and absorption rates during the experimentand of the final leaf water content make it possible to followchanges in leaf water content throughout the experiment. An account is given of the methods used for varying the speedof flow, the humidity, and the CO₂ concentration of the airstreams.     

Photoperiodic Regulation of Gametogenesis in Sea Stars, with Evidence for an Annual Calendar Independent of Fixed Daylength

SYNOPSIS. Gametogenesis and gonadal growth in the west coastsea star Pisaster ochraceus normally begins in the fall andleads to large gonads full of gametes in the spring, when spawningoccurs. The timing of gametogenesis can be shifted simply bymaintaining the animals on a seasonally changing photoperiodicregime out of phase with ambient. When they are kept on a spring-summerphotoperiodic regime during the fall and winter, gametogenesisproceeds 6 mo ahead of schedule in the following spring andsummer. Gametogenesis can be shifted out of phase even whenthe eyespots are removed. Short daylengths that normally occurduring the fall and winter are not required for gametogenesisto proceed, nor are even the long daylengths of spring and summerthat precede the initiation of gametogenesis in the fall. Thetemporal program is insensitive to fixed daylengths (LD 15:9,13:11, 12:12, 9:15) and appears to involve an endogenous calendar. Shifting the photoperiodic regime 6 mo out of phase also leadsto a shift of the gametogenic temporal program in the sea starsLeptasterias sp. (a brooder) and Asterias vulgaris (from theNew England coast), but not in the sea star Patiria miniata.Gametogenic timing also can be switched in the sea urchin Strongylocentrotuspurpuratus but the mechanism of the photoperiodic response isfundamentally different; gametogenesis requires short daylengths;continues indefinitely under a repeated short day, fall-winterphotoperiod regime, and apparently does not involve an endogenouscalendar. As photoperiodic responses are investigated furtherin these and other marine invertebrates, the models developedprimarily from studies on terrestrial organisms may need tobe extensively modified or additional new models required.     

The role of leaf defensive traits in oaks on the preference and performance of a polyphagous herbivore,Orgyia vetusta

1. Leaves possess traits that mediate the preference and performance of herbivores. Most evidence for the importance of leaf traits as defences against herbivory comes from studies of few model plant species. 2. In a phylogenetically explicit comparison, I explain the differences in preference and performance of tussock moth (Orgyia vetusta Boisduval) larvae on leaves of 27 oak (Quercus) species using nine putative leaf defences. 3. The preference for an oak species correlated positively with the survival of caterpillars. The correlation between preference and performance did not differ between oak species native to the range of tussock moth versus those from outside the herbivore's range. 4. The first principal component of leaf traits predicted survival of caterpillars on oak leaves but only marginally predicted their preference between oak species. A multiple regression model showed that evergreenness, toughness, and condensed tannin content were the best predictors of caterpillar survival, and leaf toughness was the best predictor of host preference. 5. Generalist caterpillars may accurately assess the value of novel food sources. Moreover, many leaf traits that have been found to affect herbivory within a plant species can also be used to predict the fitness of a generalist herbivore between species.