title: Dietary overlap between the non-native mosquitofish  (Gambusia affinis) and native common bully (Gobiomorphus cotidianus):  Evidence for interspecific competition?

authors: Ember, Flavian

abstract: Since their establishment in New Zealand in the 1930s, the globally invasive western mosquitofish (Gambusia affinis) has become widespread throughout lowland freshwaters, primarily in the North Island. Despite co-occurring in many ecosystems, interactions between native common bullies (Gobiomorphus cotidianus) and G. affinis are presently unknown. Like G. affinis, G. cotidianus are abundant in lowland waterways, tolerant of a wide range of environmental conditions and can consume similar prey. My research investigated the potential dietary overlap between these two species using a controlled mesocosm experiment and a stable isotope study of co-occurring G. affinis and G. cotidianus in natural lake habitats. 

Zooplankton were selected as the prey source for the mesocosm experiment. Twenty-one 100 L mesocosms were assigned either four G. cotidianus, four G. affinis, or were left as a control group (i.e., with no fish) and monitored for 14 days. Zooplankton community composition in the fish treatments was significantly different from the control tanks by Day 14 of the experiment yet did not differ significantly from one another. Both G. cotidianus and G. affinis reduced the abundances of larger crustacean zooplankton relative to the controls. This is likely to have reduced the effects of predation, competition, and physical interference by the crustaceans on rotifers, allowing rotifer species to reach numerical dominance in the treatment mesocosms by the end of the experiment. In contrast, zooplankton assemblages in the control mesocosms were dominated by cladocerans by Day 14, indicating that these had a competitive advantage in the absence of zooplanktivorous fish. 

Four Waikato lakes were selected as sites for the stable isotope study. Gambusia affinis, G. cotidianus, and basal food web taxa were collected from each lake during the austral winter of 2022. Samples were analysed for the stable carbon and nitrogen isotopes ¹³C and ¹⁵N, and results were compared to data published by Collier et al. (2018) from the same taxa and lakes during an austral summer. Mean δ¹³C values of G. affinis were significantly enriched compared to G. cotidianus at three lakes in both summer and winter, while the mean δ¹⁵N of G. affinis was significantly enriched at three lakes in summer and all lakes in winter. These differences were greatest in winter, even when the summer dataset was censored to match the winter fish length distribution. My results indicate that G. affinis and G. cotidianus are likely consuming different prey sources and that their diet is most similar during summer. Additionally, my results showed seasonal variation between lakes in the isotopic enrichment of both fish and basal food web taxa, suggesting food webs and trophic interactions may differ between sites. 

Overall, my thesis demonstrates the potential for interspecific competition between native G. cotidianus and non-native G. affinis in New Zealand through an example of zooplankton dietary overlap in a controlled experimental context. The stable isotope experiment provided mixed evidence for dietary overlap across both summer and winter in sympatric lake populations. Both experiments offer numerous future research opportunities to investigate the mechanisms behind the findings.

text: Dietary overlap between the non-native mosquitofish  (Gambusia affinis) and native common bully (Gobiomorphus cotidianus):  Evidence for interspecific competition? Since their establishment in New Zealand in the 1930s, the globally invasive western mosquitofish (Gambusia affinis) has become widespread throughout lowland freshwaters, primarily in the North Island. Despite co-occurring in many ecosystems, interactions between native common bullies (Gobiomorphus cotidianus) and G. affinis are presently unknown. Like G. affinis, G. cotidianus are abundant in lowland waterways, tolerant of a wide range of environmental conditions and can consume similar prey. My research investigated the potential dietary overlap between these two species using a controlled mesocosm experiment and a stable isotope study of co-occurring G. affinis and G. cotidianus in natural lake habitats. 

Zooplankton were selected as the prey source for the mesocosm experiment. Twenty-one 100 L mesocosms were assigned either four G. cotidianus, four G. affinis, or were left as a control group (i.e., with no fish) and monitored for 14 days. Zooplankton community composition in the fish treatments was significantly different from the control tanks by Day 14 of the experiment yet did not differ significantly from one another. Both G. cotidianus and G. affinis reduced the abundances of larger crustacean zooplankton relative to the controls. This is likely to have reduced the effects of predation, competition, and physical interference by the crustaceans on rotifers, allowing rotifer species to reach numerical dominance in the treatment mesocosms by the end of the experiment. In contrast, zooplankton assemblages in the control mesocosms were dominated by cladocerans by Day 14, indicating that these had a competitive advantage in the absence of zooplanktivorous fish. 

Four Waikato lakes were selected as sites for the stable isotope study. Gambusia affinis, G. cotidianus, and basal food web taxa were collected from each lake during the austral winter of 2022. Samples were analysed for the stable carbon and nitrogen isotopes ¹³C and ¹⁵N, and results were compared to data published by Collier et al. (2018) from the same taxa and lakes during an austral summer. Mean δ¹³C values of G. affinis were significantly enriched compared to G. cotidianus at three lakes in both summer and winter, while the mean δ¹⁵N of G. affinis was significantly enriched at three lakes in summer and all lakes in winter. These differences were greatest in winter, even when the summer dataset was censored to match the winter fish length distribution. My results indicate that G. affinis and G. cotidianus are likely consuming different prey sources and that their diet is most similar during summer. Additionally, my results showed seasonal variation between lakes in the isotopic enrichment of both fish and basal food web taxa, suggesting food webs and trophic interactions may differ between sites. 

Overall, my thesis demonstrates the potential for interspecific competition between native G. cotidianus and non-native G. affinis in New Zealand through an example of zooplankton dietary overlap in a controlled experimental context. The stable isotope experiment provided mixed evidence for dietary overlap across both summer and winter in sympatric lake populations. Both experiments offer numerous future research opportunities to investigate the mechanisms behind the findings.

year: 2023

title: Measuring ATM traffic: final report for New Zealand Telecom

authors: Cleary, John G.

subjects: computer science

abstract: The report describes the development of a low-cost ATM monitoring system, hosted by a standard PC. The monitor can be used remotely returning information on ATM traffic flows to a central site. The monitor is interfaces to a GPS timing receiver, which provides an absolute time accuracy of better than 1 µsec. By monitoring the same traffic flow at different points in a network it is possible to measure cell delay and delay variation in real time, and with existing traffic. The monitoring system characterises cells by a CRC calculated over the cell payload, thus special measurement cells are not required. Delays in both local area and wide-area networks have been measured using this system. It is possible to measure delay in a network that is not end-to-end ATM, as long as some cells remain identical at the entry and exit points. Examples are given of traffic and delay measurements in both wide and local area network systems, including delays measured over the Internet from Canada to New Zealand.

text: Measuring ATM traffic: final report for New Zealand Telecom The report describes the development of a low-cost ATM monitoring system, hosted by a standard PC. The monitor can be used remotely returning information on ATM traffic flows to a central site. The monitor is interfaces to a GPS timing receiver, which provides an absolute time accuracy of better than 1 µsec. By monitoring the same traffic flow at different points in a network it is possible to measure cell delay and delay variation in real time, and with existing traffic. The monitoring system characterises cells by a CRC calculated over the cell payload, thus special measurement cells are not required. Delays in both local area and wide-area networks have been measured using this system. It is possible to measure delay in a network that is not end-to-end ATM, as long as some cells remain identical at the entry and exit points. Examples are given of traffic and delay measurements in both wide and local area network systems, including delays measured over the Internet from Canada to New Zealand.

year: 1998-10

title: Foresight in hindsight: Visions of the future from Julius Vogel, Āpirana Ngata, Truby King, and Ettie Rout, 1889-1923

authors: Lemberg, Nicola Johanna

subjects: history

abstract: This thesis examines seven future-focused texts authored by four New Zealanders: Julius Vogel, Āpirana Ngata, Truby King, and Ettie Rout. ‘The future’ is a neglected lens for historical research and this thesis explores the value of such an approach, using New Zealand society from the 1880s and to the 1920s as a case study. A methodological combination of textual analysis, biography, and historical contexts, including consideration of print culture, allows for nuanced examination of depictions of the future, and suggests such connections are vital to fully understanding histories of the future. This research serves as a framework to inform further exploration of historical future imaginings, either in New Zealand or in other geographic or temporal contexts.

From Vogel’s novel Anno Domini 2000 (1889) to Ngata’s 1892 essay The Past and Future of the Maori to King’s and Rout’s twentieth-century guidebooks on the care of babies and the use of contraception, the four authors utilize various textual forms to communicate their imagined future, and commonly frame their ideas within concepts of utopia and dystopia. This thesis compares the futures depicted by male and female authors, and those emerging from Māori and Pākehā cultural contexts. It examines futures envisioned by politicians, community leaders, and ostracized individuals. Shaped by preoccupations with empire, gender, and identity, these future-focused texts highlight relationships between national and global spaces. This in turn allows for a fresh exploration of New Zealand’s past, and especially the country’s colonial histories.

text: Foresight in hindsight: Visions of the future from Julius Vogel, Āpirana Ngata, Truby King, and Ettie Rout, 1889-1923 This thesis examines seven future-focused texts authored by four New Zealanders: Julius Vogel, Āpirana Ngata, Truby King, and Ettie Rout. ‘The future’ is a neglected lens for historical research and this thesis explores the value of such an approach, using New Zealand society from the 1880s and to the 1920s as a case study. A methodological combination of textual analysis, biography, and historical contexts, including consideration of print culture, allows for nuanced examination of depictions of the future, and suggests such connections are vital to fully understanding histories of the future. This research serves as a framework to inform further exploration of historical future imaginings, either in New Zealand or in other geographic or temporal contexts.

From Vogel’s novel Anno Domini 2000 (1889) to Ngata’s 1892 essay The Past and Future of the Maori to King’s and Rout’s twentieth-century guidebooks on the care of babies and the use of contraception, the four authors utilize various textual forms to communicate their imagined future, and commonly frame their ideas within concepts of utopia and dystopia. This thesis compares the futures depicted by male and female authors, and those emerging from Māori and Pākehā cultural contexts. It examines futures envisioned by politicians, community leaders, and ostracized individuals. Shaped by preoccupations with empire, gender, and identity, these future-focused texts highlight relationships between national and global spaces. This in turn allows for a fresh exploration of New Zealand’s past, and especially the country’s colonial histories.

year: 2024