Structure and biology of house mouse populations that plague irregularly: an evolutionary perspective

In Australia, populations of mice occasionally irrupt into plagues, mainly in the southern and eastern grain-growing regions. Mus domesticus was the only member of the subgenus Mus identified from a genetic survey of animals collected from four states. Little is known of the origin of these mice but they probably came from Europe where plagues do not occur. We examined whether mice have evolved the ability to plague since their colonization by comparing some population parameters of Australian, European and North American mice. Their helminth fauna were contrasted to gauge the importance of founder effects on the evolution of mice in Australia.
Australian mice share 52% (12 of 23) of the helminths found in mice in Europe and North America. Those not shared mainly had indirect life cycles. The absence of species could be explained by a strong founder effect or the lack of suitable intermediate hosts near Australian ports. There was no evidence that population structure or diet had evolved differently. Population abundance was different in field populations especially during the build-up and irruption of plagues. These differences were related to better breeding by mice in Australia in field environments; average number of embryos per litter was substantially higher and breeding seasons longer. Genetic change is not the only explanation for this increased productivity–a combination of lack of interspecific competition from other granivores and more favourable climatic conditions may be responsible.
All things considered, there was no compelling evidence that Australian mice have evolved the ability to plague. Their ability to respond to good conditions by increasing litter size beyond that recorded elsewhere supports the notion that control of mouse productivity is an appropriate management option for plague prevention.     

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.     

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'.     

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.     

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.     

Habitat selection of feral cats (Felis catus) on a temperate,forested island

Abstract Habitat selection of mammalian predators is known to be influenced by availability and distribution of prey. The habitat selection of feral cats on Stewart Island, southern New Zealand, was investigated using telemetry of radio‐tagged cats. Compositional analysis of the habitat selection of radio‐tagged cats showed they were using the available habitats non‐randomly. Feral cats avoided subalpine shrubland and preferentially selected podocarp‐broadleaf forest. The avoidance of subalpine shrubland by cats was probably due to a combination of the presence of a large aggressive prey species, Norway rats Rattus norvegicus, and the lack of rain‐impervious shelter there. Most cats also used subalpine shrubland more often in dry weather than in wet weather. Cats did not preferentially select all the other habitats with only smaller rat species, Rattus rattus and Rattus exulans, present however. Cats were probably further influenced by the availability of large trees, in podocarp‐broadleaf forest, that can provide shelter. Cats were also more active in dry rather than wet weather which supports this conclusion. Home ranges of feral cats on Stewart Island were some of the largest recorded, probably because of limited primary and alternative prey.