title: Over the threshold: learning and student retention in electronic courses

authors: Scott, Jonathan B.

subjects: electronics

abstract: Retention of students in early electronics courses is a problem acknowledged worldwide. It is a particular problem in universities, such as the University of Waikato, that have a common first-year programme because students can change streams (e.g. from electrical to mechanical) at the end of the first year. It is commonly believed that the major reason for the low level of student retention is practical engagement—mechanical engineers can see and get their hands on boats, cars, propellers, cogwheels and so forth from the start, while electronics is too small to see and handle, and its workings are alien to most school leavers.

text: Over the threshold: learning and student retention in electronic courses Retention of students in early electronics courses is a problem acknowledged worldwide. It is a particular problem in universities, such as the University of Waikato, that have a common first-year programme because students can change streams (e.g. from electrical to mechanical) at the end of the first year. It is commonly believed that the major reason for the low level of student retention is practical engagement—mechanical engineers can see and get their hands on boats, cars, propellers, cogwheels and so forth from the start, while electronics is too small to see and handle, and its workings are alien to most school leavers.

year: 2010-06

title: The whole-plant compensation point as a measure of juvenile tree light requirements

authors: Lusk, Christopher H.

subjects: forest dynamics

abstract: 1.	Although ‘shade tolerance’ has featured prominently in the vocabulary of foresters and ecologists for a century, we have yet to agree on a standardized method for quantifying this elusive property. The ‘whole-plant compensation point’, interpolated from stem growth measurements across a wide range of light environments, has been proposed as a simple, robust measure of species shade tolerance. Others have argued that shade tolerance is primarily a function of differential ability to survive periods of slow growth (‘suppression’), implying that measurements of survival are vital.
2.	We measured growth of juveniles (500–1000 mm tall) of five evergreen trees over 12 months in a cool-temperate rain forest in New Zealand, to determine whether whole-plant compensation points predicted species differences in occupancy of understorey light environments, which were quantified using hemispherical photography.
3.	The five species encompassed 3•5-fold variation in whole-plant compensation points. Compensation points of most species fell within the first quartile of the distribution of light environments occupied by juveniles; they were also correlated with low-light mortality rates of juveniles, estimated from permanent plot data archived in the National Vegetation Survey Databank. Compensation points were also significantly positively correlated with height growth rates in high light, confirming the presence of the growth vs. shade tolerance trade-off detected in many other forest tree assemblages.
4.	Results show that, in temperate evergreen forests, the whole-plant compensation point distinguishes reliably between species of differing shade tolerance. Excepting situations involving parameterization of demographic models, shade tolerance can therefore be assessed without survival measurements. However, estimating whole-plant compensation points may prove more difficult in deciduous forests, where seasonal variation in understorey light transmission poses additional challenges.

text: The whole-plant compensation point as a measure of juvenile tree light requirements 1.	Although ‘shade tolerance’ has featured prominently in the vocabulary of foresters and ecologists for a century, we have yet to agree on a standardized method for quantifying this elusive property. The ‘whole-plant compensation point’, interpolated from stem growth measurements across a wide range of light environments, has been proposed as a simple, robust measure of species shade tolerance. Others have argued that shade tolerance is primarily a function of differential ability to survive periods of slow growth (‘suppression’), implying that measurements of survival are vital.
2.	We measured growth of juveniles (500–1000 mm tall) of five evergreen trees over 12 months in a cool-temperate rain forest in New Zealand, to determine whether whole-plant compensation points predicted species differences in occupancy of understorey light environments, which were quantified using hemispherical photography.
3.	The five species encompassed 3•5-fold variation in whole-plant compensation points. Compensation points of most species fell within the first quartile of the distribution of light environments occupied by juveniles; they were also correlated with low-light mortality rates of juveniles, estimated from permanent plot data archived in the National Vegetation Survey Databank. Compensation points were also significantly positively correlated with height growth rates in high light, confirming the presence of the growth vs. shade tolerance trade-off detected in many other forest tree assemblages.
4.	Results show that, in temperate evergreen forests, the whole-plant compensation point distinguishes reliably between species of differing shade tolerance. Excepting situations involving parameterization of demographic models, shade tolerance can therefore be assessed without survival measurements. However, estimating whole-plant compensation points may prove more difficult in deciduous forests, where seasonal variation in understorey light transmission poses additional challenges.

year: 2013

title: Evaluating the effects of invasive brown bullhead catfish (Ameiurus nebulosus) on kōura (freshwater crayfish, Paranephrops planifrons) in Lake Rotoiti

authors: Francis, Laura Beverley

subjects: catfish

abstract: Brown bullhead catfish (Ameiurus nebulosus) are opportunistic carnivores native to North America and were first detected in Te Weta Bay, Lake Rotoiti, in March 2016. A cordon was placed across the bay to try and contain catfish, but they had already established populations elsewhere. Spread of catfish in the lake raised concern for resident populations of freshwater crayfish or kōura (Paranephrops planifrons), which are of ecological and cultural significance to Māori. Given the limited knowledge of the potential impacts of catfish on native biota, this thesis aims to evaluate the effects of catfish on kōura in Lake Rotoiti. To do this, Bay of Plenty Regional Council (BOPRC) routine fyke netting data was used to explore species trends and relationships. A habitat survey was also conducted using whakaweku (bracken fern bundles) and fyke nets, to generate data on species’ habitat preferences and kōura metrics (e.g., sizes and sex ratios). In addition to fishing, kōura and catfish stomachs were dissected to determine diet. Potential food items of catfish were also collected for stable isotope analysis to estimate dietary overlap between catfish and kōura, and long-term resource acquisition. 

Routine BOPRC fyke netting results indicated that kōura catch per unit effort (CPUE) has declined in Lake Rotoiti, with mean catch rates dropping from 10.6 kōura net-1 night-1 in 2016 to 4.2 kōura net-1 night-1 in 2018. Over the same period, catfish CPUE has increased in the lake, with the highest catch rates in Te Weta Bay, where mean catch rates have increased from 1.1 catfish net-1 night-1 in 2016 to 63.7 catfish net-1 night-1 in 2018. Catfish catch rates were negatively associated with catch rates of kōura (r = −0.180). Mean catfish density also had a significant effect on kōura catch rates, with significantly more kōura being caught at sites without catfish. The negative association between catfish and kōura could be due to catfish eating or competing with kōura, or their differing habitat preferences. Catfish were positively associated with sites that are weedy or muddy and kōura were negatively associated with muddy habitats and were positively associated with rocky habitats. Whakaweku set at shallow depths <1 m in the lake littoral zone were ineffective at catching kōura during the habitat survey. 

Catfish diet consisted largely of chironomid larvae (Chironomidae), detritus, common bullies (Gobiomorphus cotidianus), and to a lesser extent kōura. Kōura were found in 12% of large catfish (>200 mm fork length; FL) stomachs analysed and contributed 5% volumetrically to large catfish diet. Unfortunately, the contribution of kōura to catfish diet could not be established using stable isotopes because isotopic signatures of kōura and bullies were too close to differentiate. Kōura diet consisted primarily of animal remains (common bullies and invertebrates) and detritus. Stable isotopes of carbon and nitrogen revealed that diets of kōura and catfish overlapped, with kōura sharing more of their diet with catfish than vice versa, likely reflecting catfish’s broad diet. This study suggests that catfish are responsible for the recent decline in kōura CPUE in Lake Rotoiti and that catfish are directly and indirectly affecting kōura through predation and competition for shared food resources.

text: Evaluating the effects of invasive brown bullhead catfish (Ameiurus nebulosus) on kōura (freshwater crayfish, Paranephrops planifrons) in Lake Rotoiti Brown bullhead catfish (Ameiurus nebulosus) are opportunistic carnivores native to North America and were first detected in Te Weta Bay, Lake Rotoiti, in March 2016. A cordon was placed across the bay to try and contain catfish, but they had already established populations elsewhere. Spread of catfish in the lake raised concern for resident populations of freshwater crayfish or kōura (Paranephrops planifrons), which are of ecological and cultural significance to Māori. Given the limited knowledge of the potential impacts of catfish on native biota, this thesis aims to evaluate the effects of catfish on kōura in Lake Rotoiti. To do this, Bay of Plenty Regional Council (BOPRC) routine fyke netting data was used to explore species trends and relationships. A habitat survey was also conducted using whakaweku (bracken fern bundles) and fyke nets, to generate data on species’ habitat preferences and kōura metrics (e.g., sizes and sex ratios). In addition to fishing, kōura and catfish stomachs were dissected to determine diet. Potential food items of catfish were also collected for stable isotope analysis to estimate dietary overlap between catfish and kōura, and long-term resource acquisition. 

Routine BOPRC fyke netting results indicated that kōura catch per unit effort (CPUE) has declined in Lake Rotoiti, with mean catch rates dropping from 10.6 kōura net-1 night-1 in 2016 to 4.2 kōura net-1 night-1 in 2018. Over the same period, catfish CPUE has increased in the lake, with the highest catch rates in Te Weta Bay, where mean catch rates have increased from 1.1 catfish net-1 night-1 in 2016 to 63.7 catfish net-1 night-1 in 2018. Catfish catch rates were negatively associated with catch rates of kōura (r = −0.180). Mean catfish density also had a significant effect on kōura catch rates, with significantly more kōura being caught at sites without catfish. The negative association between catfish and kōura could be due to catfish eating or competing with kōura, or their differing habitat preferences. Catfish were positively associated with sites that are weedy or muddy and kōura were negatively associated with muddy habitats and were positively associated with rocky habitats. Whakaweku set at shallow depths <1 m in the lake littoral zone were ineffective at catching kōura during the habitat survey. 

Catfish diet consisted largely of chironomid larvae (Chironomidae), detritus, common bullies (Gobiomorphus cotidianus), and to a lesser extent kōura. Kōura were found in 12% of large catfish (>200 mm fork length; FL) stomachs analysed and contributed 5% volumetrically to large catfish diet. Unfortunately, the contribution of kōura to catfish diet could not be established using stable isotopes because isotopic signatures of kōura and bullies were too close to differentiate. Kōura diet consisted primarily of animal remains (common bullies and invertebrates) and detritus. Stable isotopes of carbon and nitrogen revealed that diets of kōura and catfish overlapped, with kōura sharing more of their diet with catfish than vice versa, likely reflecting catfish’s broad diet. This study suggests that catfish are responsible for the recent decline in kōura CPUE in Lake Rotoiti and that catfish are directly and indirectly affecting kōura through predation and competition for shared food resources.

year: 2019