title: Tree species sorting along temperature gradients: How do frost-resistant traits influence competitive ability in the forest environment?

authors: FitzPatrick, Dominic Luke

subjects: forest ecology

abstract: To thrive in the forest environment a species must be able to pass each of three filters: first it must reach a site (the historical filter), then it must be able to tolerate the physical environment (the physiological filter) and finally it must be able to cope with biotic interactions at the site (the biotic filter). This thesis comprises of two complementary studies that explore the role temperature gradients play in determining a species ability to pass the physiological and biotic filters of a temperate rainforest. These studies were conducted using the seedlings of New Zealand warm- and cool- temperate tree species. The first study addresses how the trade-off in shade tolerance vs. growth rate found throughout closed-canopy forests changes from warm-temperate to cool-temperate environments using a transplant experiment. The second study aims to determine the implications of climate-related variation in xylem anatomy for morphological and physiological traits related to competitive ability. Warm-temperate species were found to be both faster-growing and more shade-tolerant than the cool-temperate species, indicating that cold resistant traits reduce competitive ability in warmer environments. This was supported by findings that the warm-temperate species had more conductive xylem and correspondingly higher levels of leaf area deployed than the cool species, indicating that cold resistance indirectly reduces the leafiness of a species. These cool-temperate species with less leaf surface area are less effective at intercepting light, resulting in lower growth rates and reduced shade tolerance which are important components of competitive ability in tree species. This may explain their absence from warmer forest environments, and their restriction to colder environments.

text: Tree species sorting along temperature gradients: How do frost-resistant traits influence competitive ability in the forest environment? To thrive in the forest environment a species must be able to pass each of three filters: first it must reach a site (the historical filter), then it must be able to tolerate the physical environment (the physiological filter) and finally it must be able to cope with biotic interactions at the site (the biotic filter). This thesis comprises of two complementary studies that explore the role temperature gradients play in determining a species ability to pass the physiological and biotic filters of a temperate rainforest. These studies were conducted using the seedlings of New Zealand warm- and cool- temperate tree species. The first study addresses how the trade-off in shade tolerance vs. growth rate found throughout closed-canopy forests changes from warm-temperate to cool-temperate environments using a transplant experiment. The second study aims to determine the implications of climate-related variation in xylem anatomy for morphological and physiological traits related to competitive ability. Warm-temperate species were found to be both faster-growing and more shade-tolerant than the cool-temperate species, indicating that cold resistant traits reduce competitive ability in warmer environments. This was supported by findings that the warm-temperate species had more conductive xylem and correspondingly higher levels of leaf area deployed than the cool species, indicating that cold resistance indirectly reduces the leafiness of a species. These cool-temperate species with less leaf surface area are less effective at intercepting light, resulting in lower growth rates and reduced shade tolerance which are important components of competitive ability in tree species. This may explain their absence from warmer forest environments, and their restriction to colder environments.

year: 2015

title: Momentum, idiosyncratic volatility and market dynamics: Evidence from China

authors: Cheema, Muhammad A.

abstract: Recent evidence on the relation between momentum and idiosyncratic volatility (IV) in the U.S. is mixed. We verify the relation between momentum and IV in China and find at best, no relation supporting the view that idiosyncratic risk is not a significant arbitrage cost for momentum returns. While the absence of a positive relation between momentum returns and IV rejects both the underreaction and the overconfidence and self-attribution stories of momentum, we find support for the overconfidence and self-attribution story from our results on market dynamics and momentum. Our results are robust when verified in other Asian markets. We also find support for the suggestion that cross-country differences in momentum returns could be the result of differences in market dynamics rather than differences in levels of individualism as suggested earlier in the literature.

text: Momentum, idiosyncratic volatility and market dynamics: Evidence from China Recent evidence on the relation between momentum and idiosyncratic volatility (IV) in the U.S. is mixed. We verify the relation between momentum and IV in China and find at best, no relation supporting the view that idiosyncratic risk is not a significant arbitrage cost for momentum returns. While the absence of a positive relation between momentum returns and IV rejects both the underreaction and the overconfidence and self-attribution stories of momentum, we find support for the overconfidence and self-attribution story from our results on market dynamics and momentum. Our results are robust when verified in other Asian markets. We also find support for the suggestion that cross-country differences in momentum returns could be the result of differences in market dynamics rather than differences in levels of individualism as suggested earlier in the literature.

year: 2017

title: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2017

authors: Hicks, Brendan J.

abstract: The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (tuna, or eels, morihana, or goldfish, and kōura, or freshwater crayfish). In the current study, we present the findings from the eleventh year of sampling (2017) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 1,110 fish and 3 kōura (18.2 kg in total) from 11 sites on 5 December 2017. The sites comprised 2,909 lineal m and 11,636 m2 in area. Kōura (freshwater crayfish) and 6 fish species were present, with common bully the most abundant species (up to 29.6 fish 100 m⁻² at the site 8, edge habitat). Goldfish (up to 14.2 100 m⁻²) was the next most abundant species, with most goldfish at sites 8 and 11 in and around the side channel. Common smelt were next the most abundant species (up to 11.4 fish 100 m⁻²). Mean density of bullies (7.8 fish 100 m⁻²) was much higher than for smelt (1.69 fish 100 m⁻²). Kōura had a patchy distribution with only 3 individuals were caught at two sites.
Comparing catches over the 11 years of sampling, the mean abundance of common bullies in 2017 was consistent with densities in most post-wall years (after 2007), but lower than in 2007 before wall closure (Newman-Keuls multiple range test, P = 0.034). The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, but low BDD did not correspond with low common bully densities. In 2017, smelt abundance had recovered somewhat from the low catches from 2014 to 2016.
Goldfish biomass increased initially (2009-2010) because of targeted fishing in the side channel (site 11), which has dense macrophytes and offers good habitat for goldfish with no flow. However, the continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers. In contrast to most previous years, no eels were caught in 2017.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 10 years of post-wall data, and comparisons of means and standard deviations suggest that the number of bullies have been lower since 2008 with the exception of 2015, when bully densities were the same as 2007, i.e., before wall closure. The large number of small juvenile bullies (<30 mm) suggests that recruitment is taking place in the channel, so fluctuating bully abundance is likely to be controlled by factors other than wall closure.

text: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2017 The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (tuna, or eels, morihana, or goldfish, and kōura, or freshwater crayfish). In the current study, we present the findings from the eleventh year of sampling (2017) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 1,110 fish and 3 kōura (18.2 kg in total) from 11 sites on 5 December 2017. The sites comprised 2,909 lineal m and 11,636 m2 in area. Kōura (freshwater crayfish) and 6 fish species were present, with common bully the most abundant species (up to 29.6 fish 100 m⁻² at the site 8, edge habitat). Goldfish (up to 14.2 100 m⁻²) was the next most abundant species, with most goldfish at sites 8 and 11 in and around the side channel. Common smelt were next the most abundant species (up to 11.4 fish 100 m⁻²). Mean density of bullies (7.8 fish 100 m⁻²) was much higher than for smelt (1.69 fish 100 m⁻²). Kōura had a patchy distribution with only 3 individuals were caught at two sites.
Comparing catches over the 11 years of sampling, the mean abundance of common bullies in 2017 was consistent with densities in most post-wall years (after 2007), but lower than in 2007 before wall closure (Newman-Keuls multiple range test, P = 0.034). The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, but low BDD did not correspond with low common bully densities. In 2017, smelt abundance had recovered somewhat from the low catches from 2014 to 2016.
Goldfish biomass increased initially (2009-2010) because of targeted fishing in the side channel (site 11), which has dense macrophytes and offers good habitat for goldfish with no flow. However, the continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers. In contrast to most previous years, no eels were caught in 2017.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 10 years of post-wall data, and comparisons of means and standard deviations suggest that the number of bullies have been lower since 2008 with the exception of 2015, when bully densities were the same as 2007, i.e., before wall closure. The large number of small juvenile bullies (<30 mm) suggests that recruitment is taking place in the channel, so fluctuating bully abundance is likely to be controlled by factors other than wall closure.

year: 2018