Oliver P. Pearson

Carnivore-Mouse Predation: An Example of its Intensity and Bioenergetics

Populations of Microtus, Reithrodontomys and Mus reached a peak in Tilden Park, California, in June 1961, and reproduction almost ceased until the following spring. The impact of carnivores (feral cats, gray foxes, raccoons and skunks) on this standing crop of mice was measured by analysis of carnivore droppings systematically recovered from a 35-acre study area. Eighty-eight per cent of the 4,400 Microtus , 33% of the 1,200 Reithrodontomys and 7% of the 7,000 Mus were eaten by the carnivores before the next spring. As Microtus became scarce, the carnivore diet included more Reithrodontomys, Mus , gophers and finally wood rats. Numerous carnivores continued to hunt mice on the area even after the mice had been practically exterminated. At the beginning of the study the standing crop per acre, in kilocalories, of various components of the food chain was: roots, 7.3 million; hay (excluding seeds), 8.1 million; seeds, 1.9 million; Microtus , 6,402; Mus , 4,543; Reithrodontomys , 434; and carnivores, 650. The annual caloric requirements of the peak populations (per acre) would have been: Microtus , 1.4 million; Mus , 876,000; Reithrodontomys , 82,000; and carnivores, 11,700. The peak population of mice could not have survived for one year on the available seed crop. The carnivores ate 55% of the calories available as mice and could have survived a full year if all mice had remained available to them, but by the end of December so many mice had been lost to other agents of mortality and by emigration that only a 12-day supply remained. In spite of the initial high density of mice, 7% of the seed crop escaped destruction and grew to form a rich vegetation in the following season.

Additional Measurements of the Impact of Carnivores on California Voles (Microtus californicus)

Predation by feral cats, raccoons, foxes, and skunks upon Microtus californicus was measured during the collapse of a dense population of voles and was found to agree well with measurements made during the preceding cycle. In 5 months the number of carnivores on the 35-acre study area dropped from 2.16 to 0.36, the number of Microtus present per carnivore varied between 224 and 880 in different months, and the percentage of the Microtus population eaten in each month varied from 33 to 5. The number of Microtus eaten per month per carnivore varied from 109 to 40. Predation pressure, measured by the ratio number of voles per number of carnivores was most intense at the end of the crash. As the vole population declined, the carnivores ate relatively more gophers, harvest mice, rabbits, birds, and reptiles. The data support the theory that carnivore predation during a crash and especially during the early stages of the subsequent population low determines to a large extent the amplitude and timing of the microtine cycle of abundance.

History of Two Local Outbreaks of Feral House Mice

Hefley, H. M. 1928. Differential effects of constant humidities on Pro toparce quinquernaculatits Haworth, and its parasite, Wiintheniia quadripustulata Fabricius. Jour. Econ. Entomol. 21:213-221. Messenger, P. S. 1959. Bioclimatic studies with insects. Ann. Rev. Entomol. 4:183-206. , and N. E. Flitters. 1954. Bioclimatic studies of three species of fruit flies in Hawaii. Jour. Econ. Entomol. 47:756-765. . 1959. Effect of variable temperature environments on egg development of three species of fruit flies. Ann. Entomol. Soc. Amer. 52:191-204. Payne, N. M. 1933. The differential effect of environmental factors upon Microbracon hebetor Say (Hymenoptera: Braconidae) and its host Ephestia kiihnliella Zeller (Lepidoptera: Pyralidae). I. Biol. Bull. 65:187205. . 1934. The differential effect of environmental factors upon Microbracow hebetor Say (Hymenoptera: Braconidae) and its host Ephestia kiihniella Zeller (Lepidoptera: Pyralidae). II. Ecol. Monogr. 4:1-46. Schlinger, E. I., and J. C. Hall. 1960. The biology, behavior, and morphology of Praon palitans Muesebeck, an internal parasite of the spotted alfalfa aphid, Therioaphis maczulata (Buckton) (Hymenoptera: Braconidae, Aphidiinae). Ann Entomol. Soc. Amer. 53: 144-160. Sekhar, P. S. 1957. Mating, oviposition, and discrimination of hosts by Aphidius testaceipes (Cresson) and Praon aguti Smith, primary parasites of aphids. Ann. Entomol. Soc. Amer. 50:370-375.

Relationships among South American Phyllotine Rodents Based on Chromosome Analysis

Study of karyotypes of almost all species of Phyllotis ( sensu stricto ) and of related genera indicates that Chinchillula , Andinomys , Neotomys , Eligmodontia , and Reithrodon are monotypic genera related to Phyllotis. Graomys ( griseoflavus and domorum ) and Auliscomys (pictus , sublimis , and holiviensis ) are given generic rank. Within the genus Phyllotis , species rank is recognized for haggardi , gerbillus , amicus , darwini , caprinus , magister , wolffsohni , definitus , andium , and osilae . Chromosomal evolution within Phyllotis seems to have progressed from 2n = 70, represented now only by osilae , to 2n = 38, represented by darwini and its close relatives.

Biology of the bamboo Chusquea culeou (Poaceae: Bambusoideae) in southern Argentina

Over a period of 7 years the biology and phenotypic variability of Chusquea culeou were studied at 5 locations in cool temperate forests of southern Argentina. Excavated rhizomes had an average of 1.1 successful rhizome buds, and an average of 2.1 years elapsed between successive generations of rhizomes. Rhizome buds usually develop within the first four years after a rhizome forms. Height, volume and weight of a culm can be calculated from its diameter 1 m above the ground. Culm size, length of foliage leaf blades, and pattern of secondary branching differed among study sites. Dead culms were numerous and commonly remained erect for more than 7 years after dying. New culm shoots appear in spring and reach full size within a few months. Shoots can grow more than 9 cm/day. Less than half of the shoots survived a year; most were killed by moth larvae. Multiple primary branch buds emerge through the culm leaf sheaths in the second spring. The mean number of branch buds at mid-culm nodes varied between 34.8 and 81.5, and the mean number of primary branches was between 22.8 and 40.8. Number and length of branches, and number and length of foliage leaf blades at each node is related to the position of the node on a culm. Most branches grow about 3 cm and produce 1 to 3 foliage leaves annually. Foliage leaf blades generally live 2 years or more; few survive 6 years. Relative lengths of foliage leaf blades and their spacing along a branch permit recognition of annual cohorts. Both gregarious and sporadic flowering have been reported, and every year a few isolated plants flower and die. Length of the life cycle is unknown. Seedlings require up to 15 years to produce culms of mature size. Foliage branches may live more than 23 years, and culms may survive 33 years. Extensive loss of new shoots to predation suggests that gregarious flowering may be driven by a need to escape parasitism. C. culeou clumps expand slowly. Average annual rate of increase of the number of live culms in a clump was 4.6%. Methods of seed dispersal are undocumented. A dense stand of Chusquea culeou had an estimated phytomass of 179 tons/hectare (dry weight), 28% of which was underground. Net annual production was about 16 t/ha dry weight.

The effect of substrate and of skin color on thermoregulation of a lizard

Abstract 1. 1. Liolaemus multiformis basks on insulating substrates instead of on rock and thereby warms about 0.6°C/min faster. 2. 2. Natural blanching of skin as Tb rises increases reflectance of red light by about 0.8% per °C Tb. 3. 3. Basking lizards sprayed with silver paint warmed almost as much and almost as fast as normal and as black lizards. Silver paint reduces absorption of visible and near i.r. energy but reduces re-radiation of thermal energy by a compensating amount.

Mice and the Postglacial History of the Traful Valley of Argentina

A 10,000-year accumulation of owl pellets in a cave in northern Patagonia contained 16 species of small mammals. The percent frequency of each species remained relatively constant throughout. Euneomys sp. was the most abundant species in every stratum of the deposit, yet today it is rarely captured by owls or by trappers. The other species caught frequently by the cave owls are abundant today. Analysis of the habitat preferences of the different rodent species shows that all of the present-day habitats probably were present during the 10,000-year period but that the area of relatively bare, windswept scree must have been proportionately greater until recent times because it is the habitat to which Euneomys is now restricted.

A stereological analysis of the ultrastructure of the lungs of wild mice living at low and high altitude.

Stereological analysis of the ultrastructural composition of the pulmonary alveolo‐capillary region of mice living at sea level compared with that of the same species (Phyllotis darwini) genetically adapted to life at 4,660 m reveals a trend at high altitude towards a greater volume percentage of tissue components. On a weight‐specific basis, non‐circulating tissue occupies a significantly greater volume in high‐altitude mice, but air space and capillary contents are not correspondingly greater. Since the arithmetic mean thickness of the tissue layers and of the air‐blood barrier are the same in the two altitudinal groups, the average alveolus must have a smaller volume in the high‐altitude mice.

New Information on Ranges and Relationships within the Rodent Genus Phyllotis in Peru and Ecuador

The karyotypes of Phyllotis amicus, darwini, gerbillus, haggardi, magister, definitus, andium , and osilae range from 70 acrocentric chromosomes in osilae to 38 metacentrics in darwini, gerbillus , and haggardi. Phyllotis pictus and sublimis both have 28 chromosomes and are clearly unrelated to the others. The sex chromosome mechanism is variable. Range extensions are reported for amicus, gerbillus, magister, definitus , and andium .

Sympatric species of Euneomys (Rodentia, Cricetidae)

A recent review lists all forms of Euneomys as a single species. We show in this report that two species live sympatrically at two localities in Chile and two in Argentina. The grooves on the anterior surfaces of the upper incisors are centrally positioned in one of the species and laterally positioned in the other. The species with central grooves has a larger head and body, larger hind foot, wider interorbital constriction, wider rostrum, longer molar toothrow, larger claws on the front feet, and lives in deep soils. The smaller species lives in bare, rocky habitat. The genus Euneomys thus comprises at least two species. The names mordax and chinchilloides are appropriate for the large and the small species, respectively.