Species In Central Chile Research Articles

Effect of a native tree on seedling establishment of two exotic invasive species in a semiarid ecosystem

Theory predicts that in more stressful environments, positive plant-plant interactions should be more important than negative ones. For instance, in arid and semiarid regions, amelioration of soil drought produced by the shade of established plants could facilitate establishment of other species, in spite of light reduction. However, this theory has not been tested widely in the context of plant invasion. In this paper we evaluated the hypothesis that in a semiarid ecosystem of central Chile, the native tree, Lithrea caustica, should facilitate through positive shading effects, the seedling establishment of two widely planted and invasive forestry species, Pinus radiata and Eucalyptus globulus. We assessed the seedling establishment examining two processes: seedling recruitment (including germination) and subsequent seedling survival. We sowed seeds (to assess recruitment) and planted 8 months old seedlings (to assess seedling survival) of each exotic species under Lithrea patches, open sites and under an artificial shade mimicking Lithrea shading. The study was repeated in a north-facing and a south-facing slope in the study area located in a xeric zone within the distribution range of plantations of these species in central Chile. Our results show that in a north-facing slope Lithrea had positive effects on recruitment of both species, which was produced by shading. These effects were counteracted by negative effects on seedling survival but through a different mechanism, which suggests that Lithrea would have no significant effect on the whole seedling establishment process of Pinus radiata nor Eucalyptus globulus in this habitat. In turn, in a south-facing slope Lithrea had no significant effect on recruitment but had a negative effect on seedling survival, which was not produced by shading. This suggests that in this habitat Lithrea has a negative effect on the seedling establishment of these exotic species. Our results suggest that the effect of the native Lithrea caustica on the seedling establishment of these exotic species is dependent upon the life-cycle phase (recruitment or seedling survival) and habitat even within the same semiarid ecosystem. In contrast to the expected positive effects Lithrea is unlikely to facilitate seedling establishment of these exotic species in this area, and in fact in some habitats this effect could be negative. However, our results also suggest that a common mechanism proposed to resist invasion in forest ecosystems such as shading, probably is not sufficient to inhibit invasion in a semiarid region.

Olfactory cues mediating prey‐searching behaviour in interacting aphidophagous predators: are semiochemicals key factors in predator‐facilitation?

AbstractBased on their effect on prey populations, predators can interact synergistically, additively, or antagonistically. Predator attraction by semiochemicals in response to herbivory is well documented; however, the possibility of semiochemicals mediating synergistic interactions has not been explored. Eriopis connexa (Germar) and Hippodamia variegata (Goeze) (both Coleoptera: Coccinellidae) interact synergistically with carabid species in Central Chile, a phenomenon in which semiochemicals may be involved. Moreover, olfactory behaviour in these coccinellids is unknown. Olfactometries contrasting non‐infested vs. infested plants with Acyrthosiphon pisum Harris (Hemiptera: Aphididae) were performed to study olfactory prey‐searching in E. connexa, H. variegata, and Trirammatus striatula (Fabricius) (Coleoptera: Carabidae). To evaluate whether semiochemicals can mediate synergistic predatory interactions, four experiments were established: olfactometries contrasting (1) infested plants with and without a predator, (2) uninfested plants with and without a predator; (3) predator vs. air, and (4) plants with previous physical activity of a predator vs. clean plants (nine combinations of predator species, according to whether they corresponded to the stimulus or focal individual). Hippodamia variegata and T. striatula were attracted to infested plants when contrasted with non‐infested plants. Infested plants with a conspecific and H. variegata elicited attraction in E. connexa, whereas T. striatula preferred infested plants with E. connexa or H. variegata. Treatments with only predators (with or without the plant) did not elicit responses, except in E. connexa which was repelled by conspecifics and H. variegata, perhaps indicating an antagonistic interaction between them; plants with previous physical activity of predators did not elicit responses. These results corroborated the importance of semiochemicals produced by herbivory in the prey‐searching behaviour of aphidophagous predators. In addition, presence of predators on the foliage may favour emission of aphid alarm pheromones, which could attract E. connexa and T. striatula. Volatiles can intervene in synergistic interactions between carabids and coccinellids; this should be replicable in other systems where predator‐facilitation between aphidophagous predators is observed.

Freezing resistance varies within the growing season and with elevation in high‐Andean species of central Chile

Predicted increases in the length of the growing season as a result of climate change may more frequently expose high-elevation plants to severe frosts. Understanding the ability of these species to resist frosts during the growing season is essential for predicting how species may respond to changes in temperature regimes. Here, we assessed the freezing resistance of 24 species from the central Chilean Andes by determining their low temperature damage (LT(50)), ice nucleation temperature (NT), freezing point (FP) and freezing resistance mechanism (i.e. avoidance or tolerance). The Andean species were found to resist frosts from -8.2 to -19.5 degrees C during the growing season, and freezing tolerance was the most common resistance mechanism. Freezing resistance (LT(50)) varied within the growing season, decreasing towards the end of this period in most of the studied species. However, the FP showed the opposite trend. LT(50) increased with elevation, whilst FP was lower in plants from lower elevations, especially late in the growing season. Andean species have the potential to withstand severe freezing conditions during the growing season, and the aridity of this high-elevation environment seems to play an important role in determining this high freezing resistance.

MACROALGAE SURVIVE DIGESTION BY FISHES1

ABSTRACTSmall individuals (<15 cm long) of the clingfish Sicyases sanguineus consume as many as 18 seaweed species in Central Chile. Enteromorpha sp. was the only species able to survive digestion by fish recently collected from the field. Enteromorpha compressa and Gelidium chilense also survived by tissue regeneration when offered as food in the laboratory, but only E. compressa showed stimulation of swarmer production. In general, our results on a vertebrate species reproduce previous findings on diverse invertebrate species. Since fish are highly motile, their capacity to disperse algal species by defecation might be of great ecological importance.

Ecological aspects of thermoregulation at high altitudes: the case of andean Liolaemus lizards in northern Chile.

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 have similar activity field temperature (Tb near 29°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°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 demonstrate body temperatures that exceed by 5°C or more, those recorded in the field.

Feeding behavior and morphological adaptations in two sympatric sea urchin species in central Chile

Feeding behavior and morphological adaptations in two sympatric sea urchin species in central Chile

Interactions in the patterns of vegetative growth and reproduction in woody dioecious plants.

Interactions between vegetative growth and reproduction were evaluated in Peumus boldus, Lithraea caustica and Laretia acaulis, three woody dioecious species in central Chile. Phenological observations were made periodically on marked branches of male and female plants, and biomass allocation (dry weight) to vegetative and reproductive tissues was measured. The magnitude of flowering was evaluated in groups of plants in three successive seasons. The patterns of activities are species- and sex-dependent, and cycles of 2-4 years have been established. Branches that produce flowers either do not grow or grow less than branches without flowers, and males and females have differential resource allocation: male branches attain higher biomass values. Groups of plants show seasonal behavior that suggest synchrony in their reproductive activities.

Population variability in the genusTrichocereus (Cactaceae) in central Chile

Trichocereus has 4 species in central Chile. Population analyses indicate that introgressive hybridization has occurred betweenT. chilensis andT. litoralis in the Valparaiso and Santiago coast ranges. A taxonomic key is presented.

Comparison of Differential Environmental Responses of Colliguaja odorifera

Summary C. odorifera , a dominant species of Central Chile, presents a highly developed lateral superficial rooting and a moderately deep tap-root system. This shrub occurs on the wet and shady south-facing slopes and also on the sunny and more xeric north-facing slopes. Solar radiation, air and soil moisture are quite different on both slopes. Hence, plants respond according to their particular environmental conditions. Shrubs growing on north-facing slopes have a higher diurnal and seasonal water stress as compared with the ones observed on the south-facing shrubs. This stress is partially overcome by a stomatal closure in the morning, a more xeromorphic leaf structure and a significant reduction of leaf size. The lesser water stress on south-facing shrubs enables them to maintain an adequate water balance. This situation is reflected on an earlier, greater and longer vegetative growth period.

INTEGRATION OF THE GENOTYPE IN GEOGRAPHIC POPULATIONS OF DROSOPHILA PAVANI

Drosophila pavani, Brncic 1957, is a common species in central Chile, and in Argentina along the eastern slope of the Andes Mountains. Its populations are polymorphic for the gene arrangements in the second and fourth chromosomes (Brncic, 1957, 1958). In chromosome II there is a gene order which differs from Standard by two constantly associated inversions (A, B) in its middle part. In the right arm of chromosome IV there exists, besides Standard, a second gene sequence due to the presence of three overlapping inversions (IV-R; A + B + C). Finally, in the left arm of the same chromosome, there is a gene arrangement which differs from Standard also by a complex of three inversions (IV-L; A + B + C). The heterozygotes for these gene orders occur in most of the populations studied with frequencies close to 50 per cent (Brncic, 1957, 1958). This suggests that the inversion heterozygotes are adaptively superior to the corresponding homozygotes. In Drosophila pseudoobscura (Dobzhansky, 1951), D. willistoni (da Cunha and Dobzhansky, 1954) and in D. robusta (Carson and Stalker, 1947) the frequencies of inversions may show geographic and seasonal changes. When populations of these species are maintained in the laboratory under certain experimental conditions, substantial changes may occur in the frequencies of the different gene orders. The situation in D. pavani seems to be different. There is no good evidence of geographic or seasonal fluctuations (Brncic, 1957, 1958, and unpublished data). Moreover, in some of the stocks maintained for more than six years under the usual laboratory conditions, it has been observed that, although the frequencies of inversions suffer some variations, they usually remain high, as in the corresponding natural populations. This seemed to indicate that D. pavani represents a single large polymorphic population, not subdivided into geographic races differing in chromosome structure. However, the adaptive function of the chromosomal polymorphism need not depend on the inversions themselves, but on the polygene complexes which they maintain (Dobzhansky and Pavlovsky, 1958). Polygenes may exhibit two types of balance (Mather, 1943; Lerner, 1958), namely internal balance, by means of which certain blocks of genes are adapted to produce superior fitness, and relational balance, established between the genes in a pair of homologous chromosomes. The chromosomal inversions are a mechanism for maintaining the integrity of such coadapted genetic systems in the population. The relational balance is responsible for the high adaptive values of inversion heterozygotes and for establishment of balanced polymorphism (Dobzhansky, 1955). There is, however, evidence that, in at least some species of Drosophila, the same inversions may carry different polygene complexes in different populations. The high fitness may be lost in the heterozygotes for chromosomes with different gene arrangements coming from distant geographic regions; the genes of one region may not give high adaptive values with the genes from other regions. This has been found in D. pseudoobscura (Dobzhansky, 1957), D. willistoni, and D. paulistorum (Dobzhansky and Pavlovsky, 1958). Thus, natural populations of these and probably of some other species, show not only qualitative and 1 The work reported in this article has been carried out under Contract Number A.T. (30-1) 2465, U. S. Atomic Energy Commission. 2 Instituto de Biologia Juan Noe. Zaniartu 1042. Santiago, Chile.