Inter-seasonal persistence and size-structuring of two minnow species within headwater streams in the Eastern Cape, South Africa
- Authors: Kadye, Wilbert T , Booth, Anthony J
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124866 , vital:35705 , https://doi.10.1111/j.1439-0426.2012.02027.x
- Description: This study examined temporal variation in population dynamics and size structuring of two cyprinid minnows, Pseudobarbus afer and Barbus anoplus, in relation to their proximate physical habitats. Population estimates were determined using three-pass depletion sampling during both summer and winter. The habitats were characterised by seasonal variation in all physico-chemical conditions and spatial variation in substrata compositions. Whereas significant differences in population size were noted between seasons for B. anoplus, no differences were found between seasons for density and capture probability for either species. An increase in boulders was associated with increase in population size and density for P. afer; for B. anoplus, increased percentages of bedrock and bank vegetation were associated with an increase in population size and probability of capture, respectively. According to Canonical Correspondence Analysis, size structuring in P. afer was explained predominantly by seasonality, with smaller length classes associated with the seasonal variable of summer, while larger length classes were associated with pH that was higher in winter. By comparison, for B. anoplus, the habitat variables – bank vegetation and bedrock – accounted for much of the explained variance for size structuring. Recruitment appeared to be the major driver of size structuring for the two species; refugia, especially boulders and bank vegetation, also appeared to be important. Overall, the two species were adapted to the headwater streams that were generally variable in environmental conditions. Potential invasions by non-native invasive fishes that occur within the mainstream habitats threaten these two species. Efforts should continue to protect these minnows from such invasions by constructing barriers to upstream migration of non-native fishes into these headwater habitats.
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- Date Issued: 2012
The nature and quality of the mathematical connections teachers make:
- Authors: Mhlolo, Michael K , Schäfer, Marc , Venkat, Hamsa
- Date: 2012
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140893 , vital:37927 , https://0-hdl.handle.net.wam.seals.ac.za/10520/EJC120887
- Description: Current reforms in mathematics education emphasise the need for pedagogy because it offers learners opportunities to develop their proficiency with complex high-level cognitive processes. One has always associated the ability to make mathematical connections, together with the teacher's role in teaching them, with deep mathematical understanding. This article examines the nature and quality of the mathematical connections that the teachers' representations of those connections enabled or constrained. The researchers made video recordings of four Grade 11 teachers as they taught a series of five lessons on algebra-related topics. The results showed that the teachers' representations of mathematical connections were either faulty or superficial in most cases. It compromised the learners' opportunities for making meaningful mathematical connections. The researchers concluded by suggesting that helping teachers to build their representation repertoires could increase the effectiveness of their instructional practices.
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- Date Issued: 2012