Modeling Global Macroclimatic Constraints on Ectotherm Energy Budgets

We describe a mechanistic individual-based model of how globalmacroclimatic constraints affect the energy budgets of ectothermicanimals. The model uses macroclimatic and biophysical charactersof the habitat and organism and tenets of heat transfer theoryto calculate hourly temperature availabilities over a year.Data on the temperature dependence of activity rate, metabolism,food consumption and food processing capacity are used to estimatethe net rate of resource assimilation which is then integratedover time. We detail and explore the significance of assumptionsused in these calculations. We present a new test of this model in which we show that thepredicted energy budget sizes for 11 populations of the lizardSceloporus undulalus are in close agreement with observed resultsfrom previous field studies. This demonstrates that model testsare feasible and the results are reasonable. Further, sincethe model represents an upper bound to the size of the energybudget, observed residual deviations form explicit predictionsabout the effects of environmental constraints on the bioenergeticsof the study lizards within each site that may be tested byfuture field and laboratory studies. Three major new improvements to our modeling are discussed.We present a means to estimate microclimate thermal heterogeneitymore realistically and include its effects on field rates ofindividual activity and food consumption. Second, we describean improved model of digestive function involving batch processingof consumed food. Third, we show how optimality methods (specificallythe methods of stochastic dynamic programming) may be includedto model the fitness consequences of energy allocation decisionssubject to food consumption and processing constraints whichare predicted from the microclimate and physiological modeling Individual-based models that incorporate macroclimatic constraintson individual resource acquisition, assimilation and allocationcan provide insights into theoretical investigations about theevolution of life histories in variable environments as wellas provide explicit predictions about individual, populationand community level responses to global climate change.     

The Effects of Ultraviolet Radiation on the Biology of Amphibians

SYNOPSIS. Potential causes for the global decline of amphibiansinclude habitat loss, disease, environmental contaminants andclimate changes. The diminishing ozone layer and consequentincrease of ultraviolet-B radiation reaching the earth's surfacehas been hypothesized to be a mortality factor, especially inhabitats otherwise undisturbed. We discuss the fundamental physicsof UV and types of biological damage after exposure. A deleteriouschange in DNA, especially the production of pyrimidine dimers,is a main effect of UVB exposure. Damaged DNA can be repairedby enzymes such as photolyase when organisms are irradiatedwith UVA or visible light. We review studies including laboratoryand field approaches on damage to amphibians from UVB exposure.Field studies in which embryos were exposed to natural sunlightor sunlight with UVB removed have shown conflicting results:some show increased embryonic mortality after UVB exposure,whereas others show that current levels of UVB are not detrimentalto amphibian embryos. The abiotic factors such as water depth,water color, and dissolved organic content of aquatic ovipositionsites effectively reduces UVB penetration through water andreduces exposure to UVB of all life history stages. Biotic factorssuch as jelly capsules around eggs, melanin pigmentation ofeggs, and color of larvae and metamorphosed forms further reduceeffectiveness of UVB penetration. We suggest areas of futureresearch to test the hypothesis of the causal connection betweencurrent UVB levels and amphibian decline.     

THE SIGNIFICANCE OF KLEPTOPARASITISM DURING THE BREEDING SEASON IN A COLONY OF ARCTIC SKUAS STERCORARIUS PARASITICUS IN ICELAND

Breeding and kleptoparasitism of Arctic Skuas was studied at Vik, Iceland, in 1973. Hatching success was 88.9%; fledging success was 0.27 fledglings per pair. The heavy chick mortality occurred mostly in the first week after hatching. In the early part of the breeding season skuas fed by robbing kittiwakes of their food at sea and by eating arthropods at the breeding grounds. At the time of hatching of skua eggs, which coincided with the hatching of Puffin eggs, skuas switched their feeding activities to kleptoparasitism of Puffins and fish so obtained was the principal item of most skuas' diet thereafter. In the first week post-hatching, the energy balance of an average adult skua pirating Puffins was estimated to be negative, but changed to positive a week later, although later, coinciding with an influx of non-breeders it turned back to negative. Arctic Terns which normally breed at Vik, and are exploited by skuas, failed to breed in 1973, and the abnormally heavy chick loss is therefore attributed to this failure of the terns. The success of the skuas kleptoparasitizing Puffins depends on the proximity of the interactions to the cliff or to the ocean, where Puffins seck refuge. Skuas catch fish mostly in the air, especially if it is dropped from high. Fish dropped from low is mostly taken by competing gulls and Ravens, which mostly control the ground and lower airspace. Skuas chasing in groups enhance their success, but the average success per member decreased with group increase. However, the success of the group-member in the ‘best’ position was equal to that of a single skua. Puffins carry 1 (large)-6 (smaller) fish, an approximately equal load irrespective of number of fish. Skuas preferentially chase Puffins carrying ‘large’ fish, thus maximizing their yield per effort. Arctic Skuas responded to changes in the numbers of arriving Puffins with a functional response, but their monitoring of the food supply was far from perfect.     

Speculations on Structural Relationships between the Hypothalamic Releasing Factors of Pituitary Hormones

RECENTLY, hypothalamic releasing factors have been isolated from two different species (porcine and ovine) and their structures elucidated^1–5. These factors stimulate the secretion of pituitary hormones and have been shown to be small polypeptides. Thyrotropin releasing factor (TRF) for both species is the tripeptide pyroglutamyl-histidyl-proline amide (pGlu-His-Pro-amide)^1,2. TRF acts on pituitary thyrotrophs to stimulate the secretion of thyroid stimulating hormone (TSH). The structure of a hypothalamic factor which stimulates the secretion of the pituitary gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH) has been determined. This gonadotropin releasing factor, referred to as LRF, is a decapeptide and, like TRF, has both terminals blocked; in both species its primary sequence is pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-amide^3–5.     

The role of habitat composition in determining breeding site occupancy in a declining Ring Ouzel Turdus torquatus population

Ring Ouzel Turdus torquatus breeding site occupancy in the Moorfoot Hills, southeast Scotland, was determined during the periods 1952–85 and 1998–2000, and sites were classed as either occupied or deserted during the latter period. Site occupancy during 1998–2000 was related to habitat data derived from a supervised classification of a Landsat 7 satellite image. Breeding sites were more likely to have remained occupied if they were at higher altitudes and had more heather cover within radii of both 200 and 450 m, although these effects became non-significant when spatial autocorrelation was accounted for. Using only topographical variables, potential breeding sites were predicted and the habitat surrounding them was compared with actual breeding sites. Actual breeding sites were more likely to have heather or grass–heather mosaic within 100 m than potential breeding sites, but there were no further habitat differences between actual and potential breeding sites within radii of 200 or 450 m. These results indicate that breeding sites at higher altitudes and with a higher cover of heather were less likely to have been deserted, and that lack of heather may prevent otherwise suitable breeding sites from becoming occupied by Ring Ouzels. More detailed field studies are needed to understand the mechanisms underlying these associations.     

Influence of moderate nutritional stress during gestation on reproduction of Collared peccaries (Tayassu tajacu)

This study examined the influences of moderate restrictions in maternal energy and protein intake during gestation on reproductive success and foetal development in the Collared peccary ( Tayassu tajacu ). Sixteen captive females from southern Texas were bred during January 1983 and randomly assigned to one of four experimental rations for the duration of gestation. Experimental diets were formulated in a factorial design with two levels of energy (HE = high, ME = moderate) and protein (HP = high, MP = moderate). Only females on the HEHP diet gained weight during gestation. Moderate restrictions of energy or protein had no influence on the number of young born alive, litter size, litter weight and length of gestation. Foetal development was only minimally affected by prolonged restrictions in protein intake. This study suggests that nutrition-related prenatal mortality between implantation and parturition may not be the most important mechanism limiting herd recruitment during moderate periods of drought in southern Texas.     

Methods and conclusions in functional analysis: a reply

This paper is a reply to criticism presented by C. R. C. Paul and R. Cowen in immediately preceding articles in Lethaia. Contrary to the assertion by Paul, the present author did not reject the paradigmatic method but (1) criticized it for its limitations and seemingly erroneous results, (2) applied it to the richthofeniacean and lyttoniacean brachiopods by use of the pump as paradigm, and (3) extended it to include anatomic, metabolic, and phylogenetic considerations that go beyond the structural and mechanistic constraints of the original formulation. The rhythmic flow mechanism was rejected primarily on the basis of evidence for a ptycholophous lophophore in the Productidina. and the relative inefficiency of 'valve flapping' in contrast to ciliary action in pumping nutrient-bearing fluid into the shell. A Chinese blast furnace was claimed by Cowen to employ a single oscillating panel as a pump, but instead this panel must act as a valve that admits air in surges while the draft in the furnace maintains unidirectional flow through the system. This is analogous to ciliary feeding in brachiopods, where undirectional flow is maintained by ciliary pumping, and the valve opens to admit water. A richthofeniid with a Composita entrapped beneath the apertural meshwork is introduced as additional evidence against the likelihood of 'valve flapping'.