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This paper shows the conceptualization of an analytical model of mathematics teacher’s specialised knowledge, which is based on the seminal work of Lee Shulman. In order to show the potential of the model, it is used here to analyze a particular case of a teacher of Spanish’ Secondary Education. The analysis shows the intertwining between different features of the knowledge of the teacher, reflecting the integrated nature of that knowledge, allowing, at the same time, a work of decomposition and synthesis of it. That will allow us to manage the design of teachers’ education, conducing also to a better understanding of mathematics teaching. Un modèle analytique des connaissances spécialisées du professeur de mathématiques est l’objet de cet article : Sa conceptualisation et sa genèse sont inspirées par les travaux fondateurs de Lee Shulman. Pour montrer le potentiel du modèle, on analyse le cas particulier d’un professeur de l’enseignement secondaire. Cette analyse met en évidence l’interrelation entre les différents aspects des connaissances du professeur, reflétant la nature intégrée de ses connaissances. En même temps elle permet un travail de décomposition et de synthèse qui peut être utilisé en formation initiale des enseignants et qui peut enrichir la compréhension de l’enseignement des mathématiques. En este artículo se mostrará la conceptualización de un modelo analítico de conocimiento especializado del profesor de matemáticas y su génesis inspirada en los trabajos seminales de Lee Shulman. Para mostrar la potencialidad del modelo, lo utilizamos para el análisis de un caso particular de un profesor de Educación Secundaria. Este análisis muestra la interrelación entre distintos aspectos del conocimiento del profesor, reflejo del carácter integrado de dicho conocimiento, pero a su vez permite una labor de descomposición y síntesis del mismo que nos facilita la intervención en la formación inicial del profesorado así como una mejor comprensión de la enseñanza de la matemática. more...

We monitored the cover and seed bank response of shrubs, perennial herbs, and ephemeral plants to experimental exclusion of both the principal rodent herbivore, Octodon degus, and its vertebrate predators from 1989 to 1994 in a semiarid Chilean mediterranean site. Although both richness and species composition of the plant community at the study site were largely determined by abiotic factors (mainly rainfall and soil nutrients), predator and herbivore exclusion had significant effects on the relative abundance of several plant species. Experimental exclusion of herbivores was associated with increased cover of some shrubs and a perennial grass, and decreased cover and seed densities of several ephemerals, especially those exotic or restricted to areas underneath shrubs. Herbivores apparently reduced shrubs through browsing and indirectly affected herb cover and seed densities by opening up areas under shrubs and/or modifying physical and chemical conditions of the soil. Plant responses to predator exclusion were less clear. Nevertheless, higher cover of some shrubs and ephemerals in the presence of predators suggests tritrophic effects through changes in small mammal densities and/or foraging behavior. more...

The role of biotic interactions including vertebrate predation and interspecific competition was studied among members of a semiarid small mammal assemblage in a long-term field manipulation in north central Chile. Fences and netting selectively excluded mammalian and avian predators, and a putative rodent competitor, the degu (Octodon degus), from large, replicated grids. Small mammal populations were censused monthly over >4 yr, and effects of predator and degu exclusions on numbers and survival of small mammals were assessed with repeated measures ANOVAs. Marginally significant predator exclusion effects were detected on 0. degus, and highly significant year X predation interactions in both wet and dry seasons; degu survival (= persistence) was also significantly longer on exclusion grids. Predation had significant effects on numbers of Phyllotis darwini, and a significant month X predator interaction existed in the wet season; survival was also sig- nificantly higher on predator exclusion grids. There was a marginally significant year X competitor interaction in the dry season for this species. Akodon olivaceus had significant month X predator and month x competitor interactions in the wet season only; survival was significantly longer on degu exclusion grids. An irruptive species, Oligoryzomys lon- gicaudatus, showed no significant predator or competitor effects in 1991-1992; however, survival was significantly longer on predator + competitor exclusion (vs. control) grids. An uncommon species, Abrothrix longipilis, had marginally nonsignificant time x com- petitor interactions but no treatment differences in survival. Finally, a second uncommon rodent, Abrocoma bennetti (not analyzed numerically) had significantly longer survival on predator exclusion grids with degus. Degus and P. darwini were significantly overrepre- sented (relative to availability) in diets of culpeo foxes (Pseudalopex culpaeus) and three nocturnal owls, respectively, whereas A. bennetti was significantly overrepresented in pred- ator diets generally. Vertebrate predation has pervasive effects on some species that, how- ever, may be related to their intrinsic demographic characteristics. Competition may be mediated by subtle behavioral interactions among assemblage members. Long-term studies are necessary to elucidate the role of biotic and abiotic factors in semiarid environments. more...

A prolonged El Nino Southern Oscillation (ENSO) event during 1991–1992 with three times the normal annual 85-mm rainfall was accompanied by major changes in numbers of small mammals at a semiarid Mediterranean site in northcentral Chile. Several demographic patterns were evident. Akodon olivaceas , an omnivore, had a rapid increase in population size of more than an order of magnitude. Phyllotis darwini , a granivore-herbivore, showed somewhat delayed, smaller increases superimposed on annual oscillations. Octodon degus , an herbivore, showed a delayed response with larger increases and extended breeding in 1992–1993. Finally, Oligoryzomys longicaudatus , a granivore, experienced increases during both a dry (1990, ppt = 32 mm) and a wet year (1992). Other species such as Abrothrix longipilis, Abrocoma bennetti , and Thylamys elegans had smaller, delayed demographic responses. Reproductive rates for the first three species were higher due to the ENSO event only in O. degus males and P. darwini as a quadratic function of time. Survival rates of all four principal species were significantly greater during the 1991–1992 ENSO. Finally, average movement between captures was lower during ENSO years, suggesting behavioral changes. Explanations for these patterns include rainfall-related increases in food-resource levels ( A. olivaceus and P. darwini ), the importance of source-sink processes in vagile species from more mesic, adjacent habitats ( O. longicaudatus ), and delayed responses to extrinsic events in species with long gestation ( O. degus, A. bennetti ). The heterogeneity of species responses suggests different capabilities for small mammals to respond to an extrinsic, large-scale event, and it emphasizes the importance of long-term studies in semiarid systems. more...

Morphological variation in the glans penis of the six genera and most species of octodontid rodents was studied and compared to members of the Abrocomidae and Ctenomyidae. Most specimens of Octodon degus, O. lunatus, O. bridgesi, Octodontomys gliroides, Aconaemys fuscus , and A. sagei presented two spikes on each side at the bottom of the intromitent sac (2–2 pattern), although the number of spikes varies from 1–2 to 4–5. The largest variability in number of spikes was shown by Spalacopus cyanus , ranging from 1–1 to 4–5; although they were rather short. The 1–1 pattern characterized Tympanoctomys barrerae and Octomys mimax . This pattern was found in the species of the genera Abrocoma and Ctenomys , which belong to the related families Abrocomidae and Ctenomyidae. Our results support the view that the 1–1 pattern is ancestral and that other patterns are derived states. Within the octodontids, only Tympanoctomys barrerae and Octomys mimax showed the ancestral condition shared with Ctenomyidae and Abrocomidae. All other octodontid genera share the derived state 2–2 or modifications of it. more...

We document the first record of Microcavia niata in the high Andes of northern Chile near the border of Bolivia. This species is restricted to bog habitats where it principally feeds on grasses and aquatic plants. Its basal metabolic rate was 0.689 ± 0.1 ml O2 g−1 h−1. Two colonies were studied, each possessing 15 and 17 individuals, and characterized by female-biased sex ratios. Individuals reacted aggressively against the intrusion of non-colony members and elicited alarm calls under risk of predation. more...

Recent reviews reveal that fossorial animals (those both foraging and sheltering underground) have influential, or even keystone, roles in the dynamics of grassland, savanna, and mediterranean scrub ecosystems (Andersen 1987; Huntly and Inouye 1988; Contreras and McNab 1990). Fossorial animals include termites and other insects, insectivorous mammals such as moles, and members of several families of herbivorous rodents, including the Geomyidae of North America and the Octodontidae of Chile (Nevo 1979; Andersen 1987). more...

The impact of the subterranean herbivorous rodent Spalacopus cyanus Molina on the herbaceous vegetation was studied by comparing biomass, species richness and species diversity at the end of the growing season in areas with and without burrows in coastal arid Chile. Total biomass was 60% higher in areas with burrows. This difference was mainly due to the large increase of Mesembryanthemum cristallinum L., a succulent prostrate annual herb. Unexpectedly, bulb biomass of geophytes, eaten by Spalacopus, did not differ between areas. However, in areas with burrows bulbs of geophytes were more numerous and smaller. It is possible that burrowing activities facilitate the occurrence of new small bulbs through seed germination. Species composition and diversity did not differ greatly between areas. Burrowing activities by Spalacopus, the life cycle of Mesembryanthemum, and climate seem to be the most important factors determining species abundance and diversity of herbs in this system. more...

Tympanoctomys barrerae, a desert specialist member of the family Octodontidae, until now thought to be conservative, and ancestral to South American hystricognath rodents, presents the highest diploid chromosome number (2n = 102) known in a mammal. Unexpectedly, its karyotype was found to be composed mainly of metacentric to sub-metacentric chromosomes. Mechanisms by which such a karyotype may have been derived are discussed. more...

We examined the ways a small diurnal rodent, Octodon degus , copes with high environmental temperatures in a semiarid region in northcentral Chile. We hypothesized that degus are constrained in use of microhabitat by their limited tolerance to high environmental temperatures as well as by presence of predators. We recorded their activity from tracks on smoked tiles, under shrubs and in the open, and in large plots with predators either present or excluded. We monitored body temperature in the two microhabitats during warm and cool seasons. Our results support our hypothesis; degus chose covered areas even when predators were absent. We conclude that thermal restriction is a factor in determining use of space by degus. more...

A study was made of the energetics of Spalacopus cyanus from high-altitude and cold burrows in the Andean Mountains and from low-altitude and warmer burrows near the Pacific Ocean in central Chile. Individuals from both populations are good thermoregulators at ambient temperatures between 2 and 30 C. They maintain a constant $T_{b}$ of 36.6 ± 0.2 (2 SE). The mass-specific BMR of S. cyanus from both populations is lower than expected from the Kleiber relationship, and it is significantly lower in individuals from high altitudes (the cooler sites) than in those from low altitudes (74% and 85%, respectively). Minimal thermal conductance (C) was 87% and 84% of that expected on the basis of $M_{b}$ for high-and lowland animals, respectively. Animals from high altitudes were larger than those from low altitudes; sexual size dimorphism occurred only at low altitudes. The combination of energetic parameters and $M_{b}$ determined a similar temperature differential between body and the lower limit of thermoneutral... more...

Etude du comportement alimentaire de D. culpaeus. Par comparaison entre la densite de proies potentielles et celle retrouvee dans les excrements des animaux, le regime alimentaire de ces animaux est examine en relation avec le milieu more...

The summer diet of Tyto alba was studied in Banos del Flaco, San Fernando, in the Andes of Central Chile. Numerically, its prey were mainly rodents (96.5%), and 20.5% of these were juveniles. The eleven species of rodents present in the area were eaten by the Barn Owl, including the fossorial species. The diet composition is indicative for the owl's activity in different microhabitats: ranging from rocky places, high in the valley, to the Andean shrub ecotone, and at lower altitudes including areas close to human settlements. Mean rodent prey size is 60 g, ranging from 20 to 220 g. The Barn Owl's ability to capture species of different sizes, behaviours, and in different habitats, as well as its ability to live in human settlements and in hard environments such as the Andean mountains may explain its widespread distribution. more...

We livetrapped small mammals for 18 months with Sherman traps, and for 13 (simultaneous) months with Tomahawk traps, in a central Chilean matorral (chaparral-like shrub-land) locality near Santiago. Eight species (the marsupial Marmosa elegans , the lagomorph Oryctolagus cuniculus , the cricetids Akodon longipilis, Akodon olivaceus, Oryzomys longicaudatus , and Phyllotis darwini , and the caviomorphs Octodon degus and Abrocoma bennetti ) were captured, with total mean densities of 57.9 and 12.4 individuals per ha in the Sherman and Tomahawk grids, respectively. Tomahawk traps provided the same estimates of density for the two largest rodents, but did not capture small species or adult rabbits. Weights of adult individuals of four species were 20–30% smaller than those reported previously. Octodon and Oryctolagus used shrub cover as available; Abrocoma avoided dense patches, whereas the remaining five species avoided sparse patches. Six mammal species were associated with the six principal shrub species in proportion to their availability, but A. longipilis and Octodon both associated with Colliguaya odorifera more frequently than expected, while apparently avoiding two other shrubs. Stopwatch-timed captures allowed categorization of one small mammal as diurnal and diurnal-crepuscular, two as nocturnal, four as nocturnal and nocturnal-crepuscular; one species was active all day, except at dawn. Comparisons with similar assemblage studies conducted in neighboring matorral areas demonstrate marked differences in population densities of particular mammal species, apparently related to levels of habitat disturbance and associated reductions of shrub cover. more...

Rates of oxygen consumption (Vo2) were measured in single, separated trios, and huddled trios of Mus musculus and Meriones unguiculatus at 5, 12, 20 and 30°C. No significant difference in Vo2 was found between the single animals and separated trios of individuals ( P > 0.05 for mice, P > 0.10 for gerbils). A significant difference in Vo2 was found between either singles or separated trios and huddled trios ( P < 0.005), except at 30°C. Absolute differences in Vo2 were greater at lower ambient temperatures; however, relative differences were independent of Ta. These results do not support a psycho-physiological component to the reduction in metabolic rate by huddled animals. Measurements on one to six separated and huddled individuals at 12.5°C support the classical explanation that reduction in metabolic rate is because of a reduction in the surface to volume ratio. When the number of huddled individuals is greater than three, the difference between observed and expected Vo2 based on the reduction of surface to volume ratio is attributed to changes in shape of the group and to increased levels of activity. more...

We studied the energetics of two herbivorous desert rodents from South America. The two species had slightly lower basal metabolic rates, lower thermal conductances, and higher temperature differentials than those expected from their body mass. Mass-independent basal rates of metabolism were higher than those reported for seed-eating desert rodents from North America. Our observations support the hypothesis that desert rodents that eat foods with high water content have higher mass-independent metabolic rates than seed-eating desert rodents. more...