In savannas, the tree–grass balance is governed by water, nutrients, fire and herbivory, and their interactions. We studied the hypothesis that herbivores indirectly affect vegetation structure by changing the availability of soil nutrients, which, in turn, alters the competition between trees and grasses. Nine abandoned livestock holding-pen areas (kraals), enriched by dung and urine, were contrasted with nearby control sites in a semi-arid savanna. About 40 years after abandonment, kraal sites still showed high soil concentrations of inorganic N, extractable P, K, Ca and Mg compared to controls. Kraals also had a high plant production potential and offered high quality forage. The intense grazing and high herbivore dung and urine deposition rates in kraals fit the accelerated nutrient cycling model described for fertile systems elsewhere. Data of a concurrent experiment also showed that bush-cleared patches resulted in an increase in impala dung deposition, probably because impala preferred open sites to avoid predation. Kraal sites had very low tree densities compared to control sites, thus the high impala dung deposition rates here may be in part driven by the open structure of kraal sites, which may explain the persistence of nutrients in kraals. Experiments indicated that tree seedlings were increasingly constrained when competing with grasses under fertile conditions, which might explain the low tree recruitment observed in kraals. In conclusion, large herbivores may indirectly keep existing nutrient hotspots such as abandoned kraals structurally open by maintaining a high local soil fertility, which, in turn, constrains woody recruitment in a negative feedback loop. The maintenance of nutrient hotspots such as abandoned kraals by herbivores contributes to the structural heterogeneity of nutrient-poor savanna vegetation.
Climate warming is likely to increase nutrient mineralization rates in bog ecosystems which may change the plant species composition. We examined the competitive relationships between two graminoid species, Eriophorum vaginatum and Rhynchospora alba, and two ericoid species, Calluna vulgaris and Vaccinium oxycoccus, at different nutrient supply rates. In a greenhouse, the plants were grown in monocultures and mixtures at four nutrient treatments: control, high N, high P, and high N ? P. The results show that the ericoids responded more strongly to the nutrient treatments than the graminoids. The dwarf shrubs showed higher growth rates and reduced root:shoot ratio at high N ? P supply. When grown in mixture the ericoids increased their growth, while graminoids decreased in biomass or showed signs of nutrient limitation compared to their monoculture plants. This suggests that under increased nutrient availability, bogs are more likely to turn into dwarf shrub dominated ecosystems and not grassland.
This study compared Dutch alumni who previously participated in an honors program (n = 72) to non-honors alumni who entered university as high-achieving high school students (n = 72) with regard to (1) final university grade point average (GPA) and (2) early career outcomes. Final grades were drawn from university files. Using an online questionnaire, participants were asked to rate themselves on work engagement and other characteristics in their current jobs. Results indicate that, compared to the non-honors control group, honors alumni had a higher study GPA at the end of their studies and higher work engagement after graduation, while job characteristics were found to be similar. Implications for educators and job recruiters are discussed.
Honours programmes have become part of higher education systems around the globe, and an increasing number of students are enrolled in such programmes. So far, effects of these programmes are largely under-researched. Two gaps in previous research on the effects of such programmes were addressed: (1) most studies lack a comparable control group of students not enrolled in honours programmes and (2) few studies have longitudinally investigated effects of honours programmes on student characteristics other than academic achievement. By using propensity score matching, the current study investigated the effects of Dutch honours programmes on students' ability, motivation, creativity and academic achievement. Students' selfperceived ability, perseverance, mastery orientation, performance orientation, intellectual curiosity and self-efficacy, as well as students' gender and study grades were used to match undergraduate honours students to non-honours students (N = 94). Results showed no overall differences in ability, motivation and creativity halfway into the honours programme, although honours students seemed to slightly increase in intellectual curiosity, while non-honours students tended to decrease in mastery orientation. Outcomes of the study give rise to considerations about the role of honours programmes in curricula.ARTICLE HISTORY
BackgroundThe achievement goal theory defines two major foci of students’ learning goals (1) primarily interested in truly mastering a task (mastery orientation), and (2) striving to show ones competences to others (performance orientation). The present study is undertaken to better understand if and how health profession students’ goal orientations change during the undergraduate program and to what degree gender, academic achievement, and self-efficacy are associated with mastery and performance orientation between students and within students over time.MethodBy means of an online questionnaire, students of medical, pharmaceutical, and veterinary sciences (N = 2402) were asked to rate themselves on mastery orientation, performance orientation, and self-efficacy at the beginning of five consecutive semesters. Data on grades and gender were drawn from university’s files. Multilevel analyses were used for data analysis.ResultsStudents’ goal orientations showed relative stability over time, but substantial fluctuations within individual students were found. These fluctuations were associated with fluctuations in self-efficacy. Students’ gender, high school grades, study grades, and self-efficacy were all associated with differences in mastery or performance orientation between students. Self-efficacy was the strongest predictor for mastery orientation and grades for performance orientation.ConclusionsThe relatively strong association between the goal orientations and students’ self-efficacy found in this study emphasizes the potential of enhancing self-efficacy in health profession students. Also, for educators and researchers, fluctuations of both goal orientations within individual students are important to consider.
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