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Browsing by Author "JAKSIC, FM"

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2 TYPES OF ADAPTATION OF VERTEBRATE PREDATORS TO THEIR PREY
(1979) JAKSIC, FM; FUENTES, ER; YANEZ, JL
A COMPARATIVE-ANALYSIS OF FOOD-NICHE RELATIONSHIPS AND TROPHIC GUILD STRUCTURE IN 2 ASSEMBLAGES OF VERTEBRATE PREDATORS DIFFERING IN SPECIES RICHNESS - CAUSES, CORRELATIONS, AND CONSEQUENCES
(1987) JAKSIC, FM; DELIBES, M
We conducted a comparative analysis of food-niche relationships and trophic guild structure in two assemblages of vertebrate predators (including hawks, owls, snakes, and carnivores) living in similar habitats of Chile and Spain, which differed in species richness (11 and 25 predator species, respectively), to explore how the structure of predator assemblages reflects an increase (or decrease) in the number of coexisting species. Our results indicate that the Spanish assemblage appears enriched by the symmetrical "addition" of species with disparately large and small values of body weight, diet breadth, and mean prey size, around the same median value found in Chile. Or, alternatively, the Chilean assemblage appears impoverished by the symmetrical "loss" of peripheral species - those at both tails of the frequency distribution of the above trophic estimators. Spanish predators overlap less extensively among themselves, and with smaller variance, than Chilean predators. Consequently, the higher predator richness in Spain is not ascribable to their narrower diet breadths or more extensive diet overlaps as predicted by some theoretical models. Instead, it is associated with a more spread-out use of the available resources. Trophic guilds can be recognized in the two countries, but in Spain guilds are less tightly packed. Some taxomically unrelated species are close diet analogues between Spain and Chile, whereas some closely related species cannot be matched well between countries. Circumstantial evidence suggests that the presence of some trophic guilds and of some specialist predators in either country is based on the high abundance attained by some particular prey types.
A LONG-TERM STUDY OF A SMALL-MAMMAL ASSEMBLAGE IN THE CENTRAL CHILEAN MATORRAL
(1989) IRIARTE, JA; CONTRERAS, LC; JAKSIC, FM
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 shrubland) 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.
BEHAVIORAL ECOLOGY OF GREY EAGLE-BUZZARDS, GERANOAETUS-MELANOLEUCUS, IN CENTRAL CHILE
(1989) JIMENEZ, JE; JAKSIC, FM
Throughout 1 year we observed the behavioral ecology of Grey Eagle-Buzzards (Geranoaetus melanoleucus) in central Chile. The eagles'' activity period was bimodal, with peaks in mid-morning and mid-afternoon. During the day they spent most of their time flying (except during winter), extensively soaring in thermal and wind updrafts, rarely using flapping flight. Eagles appeared to select specific physiographic features that favored the presence of updrafts, particularly north- and west-facing slopes and ridge tops. Use of these features apparently was unrelated to prey abundance or vegetative cover. Prey were primarily large-sized small mammals, and secondarily reptiles and birds. Although aggressive, eagles were attacked by a number of species of other raptors. Comparison of the behavioral ecology of eagles and of Nearctic buteonines demonstrated some marked differences, particularly in activity time and habitat use. These differences appear to be related to weather conditions prevailing in montane vs. lowland terrain.
BIOLOGY OF THE AUSTRAL PYGMY-OWL
(1989) JIMENEZ, JE; JAKSIC, FM
Scattered information on the Austral Pygmy-Owl (Glaucidium nanum), published mostly in Argentine and Chilean journals and books of restricted circulation, is summarized and supplemented with field observations made by the authors. Information presented and discussed includes: taxonomy, morphometry, distribution, habitat, migration, abundance, conservation, reproduction, activity, vocalization, behavior, and diet. The first quantitative assessment of the Austral Pygmy-Owl''s food habits is presented, based on 780 prey items from a single central Chilean locality. Their food is made up of insects (50% by number), mammals (32%), and birds (14%). The biomass contribution, however, is strongly skewed toward small mammals and secondarily toward birds.
BIRD ASSEMBLAGES IN TEMPERATE FORESTS OF NORTH-AMERICA AND SOUTH-AMERICA - A COMPARISON OF DIVERSITY, DYNAMICS, GUILD STRUCTURE, AND RESOURCE USE
(1991) JAKSIC, FM; FEINSINGER, P
Using available data on entire bird assemblages of temperate forests in North and South America, we compare ecological patterns and dynamics between continents and suggest a comprehensive but low-cost research program to fill some of the many conspicuous gaps in the present state of knowledge. The scanty data available for comparison suggest that ecological trends of avifaunas are reasonably similar between grossly similar forest types on the two continents, but that important dissimilarities also occur due to different phylogenies, geologic histories, compositions of vegetation, and climate. For example, fruits apparently provide a steadier resource base in South America than in North America, whereas masting seed-, nut-, and cone-bearing trees, and "masting" insect larvae seem more prevalent in North than in South America. Accordingly, the South American avifaunas studied to date contain substantial proportions of frugivores or frugivore-insectivores, whereas North American avifaunas appear to contain larger numbers of opportunistic species and/or seed-, nut-, and cone-feeding species. We propose that North American temperate forests are more heterogeneous, seasonal, dynamic, and irruptive than their South American counterparts, from a bird's eye view. The consequence could be that South American avifaunas are less opportunistic than their North American counterparts in response to spatiotemporal heterogeneity in resources or community structure; that is, they migrate less over short and long distances. Nevertheless, data are not available to test this assertion. We propose a careful comparative study of avifaunas in evergreen and nearby deciduous forests on both continents.
BODY-SIZE OF CHILEAN FOXES - A NEW PATTERN IN LIGHT OF NEW DATA
(1995) JIMENEZ, JE; YANEZ, JL; TABILO, EL; JAKSIC, FM
By using body measurements and weight data of culpeo fox Dusicyon culpaeus Molina, 1782 and chilla fox D. griseus Gray, 1837 from the Chinchilla National Reserve (north-central Chile) and Torres del Paine National Park (southern Chile), the body size distribution of Chilean foxes was analyzed and compared to data previously published by Fuentes and Jaksic (1979). Contrary to those authors, our data show that not only the larger but both species increase in size in southern Chile. Thus, latitudinal size distribution of D. culpaeus and D. griseus may not be the result of character displacement through exploitation competition, as previously interpreted, but of bioenergetic adaptations.
COMPARATIVE ECOLOGY OF DARWIN FOX (PSEUDALOPEX-FULVIPES) IN MAINLAND AND ISLAND SETTINGS OF SOUTHERN CHILE
(1990) JIMENEZ, JE; MARQUET, PA; MEDEL, RG; JAKSIC, FM
Using comparable techniques we studied the abundance, habitat use, and diet of Darwin's fox (Pseudalopex fulvipes), as well as prey availability in two constrasting settings of southern Chile: on the mainland in the Nahuelbuta ranges, and in Chiloe Island. This fox lives in sympatry with its congener P. griseus in Nahuelbuta, but is the sole fox on Chiloe Island. We estimated that Darwin's fox is about twice as abundant in Chiloe than on the mainland. The structure of the habitat where Darwin's fox was found was remarkably similar between the two study sites despite floristic differences. Its diet, however, was markedly dissimilar, with mainland foxes preying extensively on mammals and reptiles and little on insects, and island foxes preying primarily on insects and amphibians, and little on mammals. The low consumption of mammals in Chiloe may be attributed to the low densities reached by that prey on the island as compared to Nahuelbuta (estimated at about double the insular density). Fruit consumption in Chiloe was almost three times higher than in Nahuelbuta, suggesting a lower energy diet for insular foxes. We also report behavioural observations on Darwin's fox provided by knowledgeable sources.
CORRELATES OF TAIL LOSSES IN 12 SPECIES OF LIOLAEMUS LIZARDS
(1980) JAKSIC, FM; FUENTES, ER
The relative frequencies of naturally occurring tail losses in 12 spp. of central Chile Liolaemus [L. altissimus, L. chiliensis, L. fuscus, L. lemniscatus, L. leopardinus, L. monticola, L. nigromaculatus, L. nigroviridis, L. nitidus, L. platei, L. schroederi and L. tenuis] are reported. Percentages vary between 23.8-77.2%. In an attempt to explain these differences, percent tail loss was correlated with an estimate of time exposed to predators (size of the lizards), with an estimate of intraspecific susceptibility to predators (sexual dimorphism), and with percent occupation of conspicuous perches. Partial correlation analysis exhibited statistical significance only with the latter variable suggesting that visibility to predators could be causally related to tail losses. Frequency of tail loss is not a measure of predation pressure, but of successful escapes after at least 1 close encounter with a predator.
DISCOVERY OF A CONTINENTAL POPULATION OF THE RARE DARWIN FOX, DUSICYON-FULVIPES (MARTIN, 1837) IN CHILE
(1990) MEDEL, RG; JIMENEZ, JE; JAKSIC, FM; YANEZ, JL; ARMESTO, JJ
The rare Darwin''s fox Dusicyon Fulvipes (Martin, 1837) was thought to be restricted to Chiloe Island in southern Chile, and to be a subspecies of Dusicyon griseus. We report the findings of a continential population of D. fulvipes, 600 km north of its known insular ranges and in sympatry with D. griseus. We document for the first time the food habits of Darwin''s fox, add new information on its morphometry, and discuss the systematic, zoogeographic and ecological implications of the discovery of the continental population.
ECOLOGICAL ASPECTS OF THERMOREGULATION AT HIGH-ALTITUDES - THE CASE OF ANDEAN-LIOLAEMUS LIZARDS IN NORTHERN CHILE
(1989) MARQUET, PA; ORTIZ, JC; BOZINOVIC, F; JAKSIC, FM
We document activity field temperatures, daily activity patterns, and extent of thermoregulation in four species of Liolaemus lizards inhabiting at high altitude (above 3500 m) in the Andes of northern Chile. These four species similar activity field temperature (Tb near 29.degree.C) despite their being distributed at different altitudinal belts. However, conspicuous differences exist between higher-altitude (L. alticolor and L. jamesi) and lower-altitude (L. islugensis and L. ornatus) lizards regarding extent of thermoregulation and activity period. Some differences in morphology, behavior, and patterns of microhabitat occupancy are also apparent among these four species and are seemingly related to the thermal environment to which they are subjected. In comparison to eight low-altitude Liolaemus species in central Chile (Tb near 35.degree.C) the four high-altitude species in northern Chile have lower activity field temperature. The latter is apparently due to the constraints imposed by the harsh Andean thermal environment, a hypothesis supported by the fact that high-altitude Liolaemus lizards under laboratory conditions demonstrated body temperatures that exceed by 5.degree.C or more, those recorded in the field.
ECOLOGICAL SPECIES REPLACEMENT OF LIOLAEMUS LIZARDS ALONG A HABITAT GRADIENT
(1980) FUENTES, ER; JAKSIC, FM
Ecological species replacement of L. platei by L. lemniscatus may occur along a north-south oriented herb density gradient. Both congeners are the only ground-dwelling lizards in the area; this suggests that L. lemniscatus is an ecological counterpart of L. platei in herbaceous habitats. Relatively longer legs may be associated with the utilization of herb-free habitats by L. platei; the shorter legs possessed by L. lemniscatus are associated with the utilization of habitats of higher herb density. Morphological evidence indicates the presence of intermediate populations in the zone of intermediate herb density. Alternatives of a single-species cline vs. interspecific hybridization between the 2 taxa are discussed.
ECOLOGICAL, MORPHOLOGICAL, AND BIOENERGETIC CORRELATES OF HUNTING MODE IN HAWKS AND OWLS
(1985) JAKSIC, FM; CAROTHERS, JH
We examined four correlates of hunting mode, dichotomized as active search (AS) and sit-and-wait (SW), in five assemblages of sympatric hawks and owls. Examining twenty-four hawk and ten owl species we found that: (1) Linearized wing loadings are light for kites, harriers, and eagles (which are primarily AS), and heavy for buteonines, falcons, and accipiters (which are mixed-mode hunters using both AS and SW techniques). Primarily AS-owls (mainly strigines and tytonines) have light linearized wing loadings, whereas SW-owls (mainly bubonines) are more heavily loaded. AS-hawks do not differ significantly from AS-owls, nor do SW-hawks from SW-owls; (2) Among hawks, diet breadth increases from accipiters through harriers, to falcons, eagles, buteonines, and to kites; and among owls, from strigines through bubonines to tytonines. No significant differences in diet breadth are detected between AS and SW hawks (or owls), nor between single-mode and mixed-mode hawks (or owls); (3) Among hawks, the ratio prey mass/body mass (PM/BM) increases from harriers through falcons to buteonines, accipiters, eagles, and to kites, and from tytonines through strigines to bubonines, among owls. No significant differences in the ratios PM/BM are found between AS and SW hawks (or owls); (4) Energetic costs incurred per prey capture are greater with the AS than with the SW mode inthree out of four cases analyzed, but information on energetic gains are available for only one. Here, AS rendered a larger differencebetween benefit and cost than did SW; in the other three cases that differential was not known, but several advantages associated to AS were claimed to offset its high energetic cost. Our main conclusions are: (1) Calculation of linearized wing loading of a hawk (or owl) enables prediction of its main hunting mode; (2) Although use of AS or SW techniques (singly or in combination) seems not to constrain access of raptors to prey resources (in terms of diversity and size), further studies focusing on single subfamilies are likely to detect differences in prey use by raptors using different techniques; (3) Little can be predicted about the extent of hunting modes used by different raptors, until the associated energetic gains are evaluated.
ECOLOGY AND BEHAVIOR OF SOUTHERN SOUTH-AMERICAN CINEREOUS HARRIERS, CIRCUS-CINEREUS
(1988) JIMENEZ, JE; JAKSIC, FM
We report field observations made in Torres del Paine National Park, southernmost Chile, on the ecology and behavior of breeding cinereous harriers (Circus cinereus) and summarize scattered information on the biology of this species. Information is presented and discussed on: taxonomy, morphology, distribution, habitat, migration, abundance, status, reproduction, behavior, and diet. Reproductive aspects of the population studied are documented with emphasis on behavior; 1620 min of observations on prey transport and transfer are analyzed quantitatively. The first quantitative assessment of the cinereous harrier''s diet is also presented, based on 1259 prey items identified among 413 regurgitated pellets collected in the study site: 33.6% of the prey (by number) was insects, 27.2% birds, 19.1% each, mammals and reptiles, and 1.0% arachnids. The biomass contribution to the diet, however, follows a decreasing order from birds, through mammals, reptiles, insects, and to arachnids.
EFFECTS OF VERTEBRATE PREDATION ON A CAVIOMORPH RODENT, THE DEGU (OCTODON-DEGUS), IN A SEMIARID THORN SCRUB COMMUNITY IN CHILE
(1993) MESERVE, PL; GUTIERREZ, JR; JAKSIC, FM
The effects of vertebrate predation have been monitored since 1989 on 16 replicated 0.56 ha study plots in a semiarid thorn scrub community in north-central Chile. Using fences of different heights with and without holes and suspended game netting to alter principal predator (foxes and raptors) and large rodent herbivore (Octodon degus) access, four grids each have been assigned to the following treatments: 1) low fencing and holes allowing free access of predators and small mammals; 2) low fencing without holes to exclude degus only, 3) high fencing and netting with holes to exclude predators only; and 4) high fencing and netting without holes to exclude predators and degus. Small mammal population censuses are conducted monthly using mark-recapture techniques. Degu population trends during 1989 and 1990 showed strongly but nonsignificantly lower numbers in control plots during months when densities were characteristically low (September November) for this seasonally reproductive species; since March 1991, differences have become persistent and increasingly significant. Predators appear to have greater numerical effects when their prey populations are low. Survival times of degus, particularly established adults, were significantly longer in predator exclusion grids during the 2 1/2 years of observation; thus, predation also affects prey population structure.
EUROPEAN RABBITS VERSUS NATIVE RODENTS IN CENTRAL CHILE - EFFECTS ON SHRUB SEEDLINGS
(1983) FUENTES, ER; JAKSIC, FM; SIMONETTI, JA
The importance of the introduced rabbit Ooryctolagus cunicueus and of the native rodent Octodon degus (= degu) as browsers of shrub seedlings in the central Chilean evergreen shrublands (-matorral) was experimentally assessed. Seedlings were planted in several spatial arrangements in 2 open successional stands and in 2 mature stands of different cover and exposure. The browsing impact of rabbits and degus was evaluated separately after .apprx. 1 yr since the start of the experiments. Degus cause important seedling mortality only within a 5 m-radius centered at the border of their retreats. Rabbits cause heavier seedling mortality, forage more widely and, consequently, have a greater impact than do degus. Rabbits may be halting the secondary succession process, shifting the matorral composition toward less palatable shrub species, and/or broadening the spacing between shrub clumps.
EXPERIMENTAL-EVIDENCE THAT HIGH POPULATION FREQUENCIES OF LIZARD TAIL AUTOTOMY INDICATE INEFFICIENT PREDATION
(1988) MEDEL, RG; JIMENEZ, JE; FOX, SF; JAKSIC, FM
Frequency of autotomized tails in lizard populations has been taken as an indicator of predation pressure upon those populations. However, recent correlational evidence points to autotomy as reflecting lizards'' escape efficiencies and/or predators'' attack inefficiencies. We report experimental evidence on the relative inefficiencies of three predator species (a teiid, a snake, and a falcon) as autotomy-producing agents, and on the relative escape efficiencies of three congeneric lizard species under laboratory conditions. The falcon was the least inefficient lizard predator (100% of successful attacks) whereas the teiid and snake were more inefficient (10-20% of the lizards escaped by autotomizing their tail). Lizards that successfully escaped predation by the widely-foraging teiid had relatively longer tails than unsuccessful ones. No difference in this feature was detected between successful and unsuccessful lizards attacked by the sit-and-wait snake. All three lizard species were equally efficient at escaping the three predators through tail autotomy. Our observed differences of comparative inefficiencies of lizard predators give experimental support to assertions that tail-loss frequencies do not adequately serve as indices of presumed predatation pressure. High rates of tail-loss among lizard populaions could instead reflect attempts at predation by inefficient predators.
FEEDING ECOLOGY OF THE BARN OWL IN CENTRAL CHILE AND SOUTHERN SPAIN - A COMPARATIVE-STUDY
(1980) HERRERA, CM; JAKSIC, FM
The food habits of the barn owl (T. alba) in the Mediterranean-climate areas of central chile and southern Spain were examined. In both areas most prey were small mammals (95% and 87% in Chile and Spain, respectively). Spanish barn owls frequently fed on reptiles and amphibians (4.5% of the diet), whereas such prey were not consumed by Chilean barn owls. The most noticeable difference involved mean body weight of small mammal prey (70.7 g in Chile vs. 21.2 g in Spain), which was associated with the different weight ranges of small mammals present in the 2 areas (40-320 g in Chile vs. 2.5-390 g in Spain). The narrower diet and specialization on mammals by Chilean barn owls was probably accounted for by the greater availability of larger small mammals and also perhaps by their greater overall density. In spite of the different prey weights taken by the owls, their body weights were similar in the 2 areas. These results are discussed in relation to the species configuration of the owl communities in Chile and Spain.
HETEROGENEOUS RESPONSES OF SMALL MAMMALS TO AN EL-NINO SOUTHERN-OSCILLATION EVENT IN NORTHCENTRAL SEMIARID CHILE AND THE IMPORTANCE OF ECOLOGICAL SCALE
(1995) MESERVE, PL; YUNGER, JA; GUTIERREZ, JR; CONTRERAS, LC; MILSTEAD, WB; LANG, BK; CRAMER, KL; HERRERA, S; LAGOS, VO; SILVA, SL; TABILO, EL; TORREALBA, MA; JAKSIC, FM
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 olivacerrs, 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, Oligorzyzomys longicaudatus, a granivore, experienced increases during both a dry (1990, ppt = 32 mm) and a wet year (1992). Other species such as Aborthrix longipilis, Abrocoma bennetti, and Thylamys elegans had smaller, delayed demo,oraphic responses. Reproductive rates for the first three species were higher due to the ENSO event only in O. negus 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.
LIZARDS AND RODENTS - EXPLANATION FOR THEIR RELATIVE SPECIES-DIVERSITY IN CHILE
(1979) FUENTES, ER; JAKSIC, FM

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