Ecology
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Competition Between Two Chipmunk Species (Eutamias) Two chipmunk species were studied in the mountains of western Alberta from 1961 to 1965. One species, Eutamias minimus, is largely confined to alpine habitat but also ranges into subalpine forest, where its distribution narrowly overlaps that of E. amoenus. The fundamental niches of the two species, estimated from their habitat distributions elsewhere, are both reduced in western Alberta. Mark and recapture trapping in an overlap zone showed that neither species selected habitat deficient in cover and both species made the same relative use of the available forest. The boundary between the two species was not clearly predictable by obvious habitat features. Eutamias amoenus luteiventris is larger than E. minimus oreocetes and, on an average, has larger litters, earlier maturity, and higher populations density. The two species take similar foods, depending on availability in their respective habitats, but the food consumption of individual minimus is less than that of amoenus. In the laboratory, amoenus was highly successful in interspecific encounters with minimus, regardless of whether or not minimus was a resident of the observation cage. In addition, amoenus dominated minimus in a mixed—species group and minimus exhibited avoidance behavior under such conditions. The highly developed aggressive behavior of Eutamias amoenus enables it to exclude E. minimus from subalpine habitats, but the latter survives in alpine situations where its small size is an adaptation to a reduced food supply.
Ecology - Tập 52 Số 2 - Trang 320-329 - 1971
Mechanisms of Competitive Exclusion Between Two Species of Chipmunks Two species of chipmunks, Eutamias dorsalis and E. umbrinus exclude each other from certain elevations on isolated mountain ranges in the central Great Basin. Competitive success is determined by habitat; dorsalis excludes umbrinus from the sparse pinon—juniper forests at lower elevations and umbrinus excludes dorsalis from the denser forests at higher altitudes. The two species occur together only in a very narrow strip of intermediate habitat. Observation of the behavior and interactions of the two species within this overlap zone resulted in the following explanation for the mutual exclusion. E. dorsalis, the more aggressive and more terrestrial species, chases umbrinus from those areas where the trees are so widely spaced that umbrinus must flee on the ground. The competitive advantage immediately shifts to the more social and arboreal umbrinus when the trees are sufficiently large and dense that their branches interlock. In these habitats umbrinus readily escapes dorsalis by fleeing through the trees over routes that the more aggressive species cannot follow. In such situations the aggressive nature of dorsalis actually becomes competitively disadvantageous because the more social umbrinus is so numerous that dorsalis wastes a great deal of time and energy on fruitless chases. The differences between the two species in aggressive behavior apparently represent adaptations to the density of cover and food resources in their habitats. The main mechanisms of the competitive interaction between these two chipmunks (interspecific aggression, the ability of the subordinate species to utilize some feature of the habitat to escape from the dominant species, and aggressive neglect on the part of the dominant species) may frequently be important in cases of competitive exclusion between highly mobile animals.
Ecology - Tập 52 Số 2 - Trang 305-311 - 1971
Altitudinal Zonation of Chipmunks (Eutamias): Interspecific Aggression Eutamias alpinus, E. speciosus, E. amoenus, and E. minimus are contiguously allopatric on the eastern slope of the Sierra Nevada, California. This paper is part of a study of the factors determining the lines of contact between these contiguously allopatric populations. Overlapping fundamental niches and overlapping realized niches indicate that competitive exclusion has occurred. Patterns of intra— and interspecific aggression are described for these four species. The aggressive dominance of alpinus and amoenus explain the limited realized niches of speciosus and minimus. Hypotheses regarding the evolution of the patterns of aggressive behavior observed in these species are suggested. Aggression has been selected for in alpinus and amoenus because of a seasonal, potentially limited food supply which is economically defendable. Aggression has not been selected for in minimus because it is not metabolically feasible to engage in aggressive interactions in the hot sagebrush desert. Aggressive behavior has not been selected for in speciosus probably because of predator pressure and the seasonal abundance of food in its habitat.
Ecology - Tập 52 Số 2 - Trang 312-319 - 1971
Synergism and context dependency of interactions between arbuscular mycorrhizal fungi and rhizobia with a prairie legume Biotic interactions play primary roles in major theories of the distribution and abundance of species, yet the nature of these biotic interactions can depend upon the larger ecological community. Leguminous plants, for example, commonly associate with both arbuscular mycorrhizal fungi (AMF) and rhizobia bacteria, and the pairwise interactions may depend upon the presence or identity of the third partner. To determine if the dynamics of plant–AMF and plant–rhizobia interactions are affected by the alternate symbiont, we manipulated the presence and identity of each symbiont, as well as levels of the nutrients supplied by each symbiont (nitrogen and phosphorus), on the growth of prairie legume Amorpha canescens . We found strong synergistic effects of AMF and rhizobia inoculation on plant biomass production that were independent of nutrient levels. AMF and rhizobia responses were each influenced by the other, but not in the same direction. AMF infection increased root nodule number and mass, but rhizobia inoculation decreased AMF hyphal colonization of roots. The relative benefits of each combination of symbionts depended upon phosphorus level. The effect of nitrogen was also contingent on the biotic environment where nitrogen addition decreased nodulation, but this decrease was reduced with coinfection by AMF. Our results demonstrate a strong contingency on the co‐occurrence of AMF and rhizobia for the long‐term fitness of A. canescens , and suggest that the belowground community is critical for the success of this species in tallgrass prairies.
Ecology - Tập 95 Số 4 - Trang 1045-1054 - 2014
Defoliation and arbuscular mycorrhizal fungi shape plant communities in overgrazed semiarid grasslands Abstract Overgrazing substantially contributes to global grassland degradation by decreasing plant community productivity and diversity through trampling, defoliation, and removal of nutrients. Arbuscular mycorrhizal (AM) fungi also play a critical role in plant community diversity, composition, and primary productivity, maintaining ecosystem functions. However, interactions between grazing disturbances, such as trampling and defoliation, and AM fungi in grassland communities are not well known. We examined influences of trampling, defoliation, and AM fungi on semiarid grassland plant community composition for 3 yr, by comparing all combinations of these factors. Benomyl fungicide was applied to reduce AM fungal abundance. Overgrazing typically resulted in reduced dominance of Stipa Krylovii , contributing to degradation of typical steppe grasslands. Our results indicated trampling generally had little effect on plant community composition, unless combined with defoliation or AM fungal suppression. Defoliation was the main component of grazing that promoted dominance of Potentilla acaulis over Stipa krylovii and Artemisia frigida , presumably by alleviating light limitation. In non‐defoliated plots, AM fungi promoted A. frigida , with a concomitant reduction in S. krylovii growth compared to corresponding AM suppressed plots. Our results indicate AM fungi and defoliation jointly suppress S. krylovii biomass; however, prolonged defoliation weakens mycorrhizal influence on plant community composition. These findings give new insight into dominant plant species shifts in degraded semiarid grasslands.
Ecology - Tập 99 Số 8 - Trang 1847-1856 - 2018
Litter Decomposition on the Mauna Loa Environmental Matrix, Hawai'i: Patterns, Mechanisms, and Models We determined controls on litter decomposition and nutrient release for the widespread native tree Metrosideros polymorpha in 11 sites arrayed on gradients of elevation, precipitation, and substrate age on Hawaiian lava flows. The effects of site characteristics were evaluated using three common substrates (Metrosideros leaf litter from one of the sites, wood dowels, and filter paper) decomposed in each of the sites, and the inherent decomposability of tissue (substrate quality) was evaluated using Metrosideros leaf litter from each of the sites decomposed in a common site. Site characteristics were responsible for most of the variation in rates of decomposition in the range of sites and substrates examined. Common substrates decomposed much more rapidly in warm, low elevation sites; apparent Q1 0 values, calculated on the basis of variation in mean annual temperature with elevation on individual lava flows, ranged from 4 to 11. Litter decomposed slowly in the dry sites, but leaf litter produced in the dry sites decomposed more than twice as rapidly as litter from wet sites when both were measured in the same site. The higher substrate quality of litter from dry sites could be due to trade—offs among nutrient—use efficiency, water—use efficiency, and carbon gain by water—limited Metrosideros. We used these results to test a revision of the CENTURY soil organic matter model that had been designed to simulate the decomposition of surface litter. Simulations accurately matched the pattern but underestimated the magnitude of among—site differences in the decomposition of common substrates in a range of sites. Analyses of both field and simulation results suggested that the decomposition of Metrosideros leaf litter could be limited by nitrogen availability.
Ecology - Tập 75 Số 2 - Trang 418-429 - 1994
CLIMATE AND DISTURBANCE FORCING OF EPISODIC TREE RECRUITMENT IN A SOUTHWESTERN PONDEROSA PINE LANDSCAPE
Ecology - Tập 86 Số 11 - Trang 3030-3038 - 2005
CLIMATIC AND HUMAN INFLUENCES ON FIRE REGIMES OF THE SOUTHERN SAN JUAN MOUNTAINS, COLORADO, USA
Ecology - Tập 85 Số 6 - Trang 1708-1724 - 2004
Presettlement Regeneration Patterns in a Southwestern Ponderosa Pine Stand Tree stems @>106 yr old (i.e., established before significant European influence in this area) in a 7.3—ha old—growth ponderosa pine (Pinus ponderosa) forest in northern Arizona were aged and mapped. Age structure analysis showed that successful establishment of ponderosa pine was infrequent. The periods without successful establishment could be quite long, as suggested by four consecutive decades in which only two surviving trees were established. The stems were strongly aggregated, as measured with nearest neighbor analysis, and groups were visually distinct in the field. Most of the stems occurred in groups of three or more, with group size ranging from 3 to 44 stems and area occupied by a group ranging from 0.02 to 0.29 ha. Ages of stems within groups were variable, the most homogeneous group having a range of 33 yr and the least having a range of 268 yr. The data are not consistent with the commonly held view that southwestern ponderosa pine occurs in even—aged groups and that each group became established following the demise of the group previously occupying the site. Instead, it seems more likely that seedlings became established when one or two trees within the group died, the additional fuel surrounding the dead trees causing an intensely burned spot in the otherwise low—intensity fires that were frequent in the area. The hot spot would create a potential seedbed for pine by eliminating, at least temporarily, the competing grasses on that small area. This decreased competition, in conjunction with adequate seed production and favorable moisture conditions in the spring and early summer, may well have been critical for ponderosa pine establishment. The relative infrequency of all these events occurring in the necessary sequence could explain the erratic age structure data from this area.
Ecology - Tập 66 Số 2 - Trang 589-594 - 1985
A gentle floriphilic katydid <i>Phaneroptera brevis</i> can help with the pollination of <i>Bidens pilosa</i>
Ecology - Tập 99 Số 9 - Trang 2125-2127 - 2018
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