title: Do benthic macrofauna functional groups or their key constituent species better predict variation in ecosystem functioning?

authors: Petersen, Grady

subjects: Marine science

abstract: Estuarine ecosystems are important zones for primary productivity and nutrient processing, have rich communities of plants and animals and support important fisheries and are fundamental to food webs. Intertidal habitats in estuaries are highly dynamic environments, subject to tidal variation and often have strong environmental gradients of salinity, turbidity and bed sediment grain size. These environmental factors contribute to the diversity of macrofaunal assemblages which vary over a range of spatial and temporal scales. This study was based in the Manukau Harbour, New Zealand, and aimed to investigate the spatial variation of nutrient processing within the harbour, and whether this variation is best explained by biotic or abiotic variables. Additionally, DistLM models were employed to find if either macrofauna functional groups or key species in these groups serve as better predictors of ecosystem function.
To provide empirical information to a project designing a whole-estuary nutrient mixing model, a team of ecologists deployed benthic incubation chambers (0.25 m2) to measure solute fluxes, and assessed the macrofauna community and sediment characteristics at 6 intertidal sandflat sites in the Manukau Harbour over a 4 day period in December 2016. Denitrification rates were measured at 2 sites to provide information on nitrogen removal from the harbour. This thesis deals specifically with how the macrofaunal communities and how they relate to and influence nutrient fluxes.
Macrofauna collected from the Manukau Harbour were assigned functional groups based on species specific traits. Multiple regression models were performed using functional groups and ecosystem variables as predictors, and dark chamber fluxes of O2, NH4+ and NOx- as response variables. Significantly correlated functional groups (p < 0.05) were substituted for their constituent species to determine whether functional groups or individual species served as better predictors of ecosystem functioning. 
The results indicated that while functional groups may provide redundancy in terms of multiple species carrying out similar functional roles, there are key species that dominate these roles. In addition to the macrofauna functional groups, several environmental variables (mud content, phaeophytin biomass and organic content) served as important predictors for changes in ecosystem functioning. 
This suggests that macrofauna functional groups form complex relationships with environmental variables which influence ecosystem functioning through benthic metabolism and excretion and macrofaunally-mediated such as bioturbation and irrigation of sediments. These biological processes alter the oxic-anoxic boundaries and facilitate the breakdown and remineralisation of deposited organic matter, fuelling primary productivity and nitrogen cycling.
At two sites where denitrification was measured, the total amount of nitrogen leaving the water column was similar (242.3 and 234.8 µmol N m-2 h-1), however the rates of denitrification of these sites was significantly (p = 0.0001) different, suggesting that permanent removal of nitrogen varies spatially across the harbour, which can have important connotations for ecosystem management.

text: Do benthic macrofauna functional groups or their key constituent species better predict variation in ecosystem functioning? Estuarine ecosystems are important zones for primary productivity and nutrient processing, have rich communities of plants and animals and support important fisheries and are fundamental to food webs. Intertidal habitats in estuaries are highly dynamic environments, subject to tidal variation and often have strong environmental gradients of salinity, turbidity and bed sediment grain size. These environmental factors contribute to the diversity of macrofaunal assemblages which vary over a range of spatial and temporal scales. This study was based in the Manukau Harbour, New Zealand, and aimed to investigate the spatial variation of nutrient processing within the harbour, and whether this variation is best explained by biotic or abiotic variables. Additionally, DistLM models were employed to find if either macrofauna functional groups or key species in these groups serve as better predictors of ecosystem function.
To provide empirical information to a project designing a whole-estuary nutrient mixing model, a team of ecologists deployed benthic incubation chambers (0.25 m2) to measure solute fluxes, and assessed the macrofauna community and sediment characteristics at 6 intertidal sandflat sites in the Manukau Harbour over a 4 day period in December 2016. Denitrification rates were measured at 2 sites to provide information on nitrogen removal from the harbour. This thesis deals specifically with how the macrofaunal communities and how they relate to and influence nutrient fluxes.
Macrofauna collected from the Manukau Harbour were assigned functional groups based on species specific traits. Multiple regression models were performed using functional groups and ecosystem variables as predictors, and dark chamber fluxes of O2, NH4+ and NOx- as response variables. Significantly correlated functional groups (p < 0.05) were substituted for their constituent species to determine whether functional groups or individual species served as better predictors of ecosystem functioning. 
The results indicated that while functional groups may provide redundancy in terms of multiple species carrying out similar functional roles, there are key species that dominate these roles. In addition to the macrofauna functional groups, several environmental variables (mud content, phaeophytin biomass and organic content) served as important predictors for changes in ecosystem functioning. 
This suggests that macrofauna functional groups form complex relationships with environmental variables which influence ecosystem functioning through benthic metabolism and excretion and macrofaunally-mediated such as bioturbation and irrigation of sediments. These biological processes alter the oxic-anoxic boundaries and facilitate the breakdown and remineralisation of deposited organic matter, fuelling primary productivity and nitrogen cycling.
At two sites where denitrification was measured, the total amount of nitrogen leaving the water column was similar (242.3 and 234.8 µmol N m-2 h-1), however the rates of denitrification of these sites was significantly (p = 0.0001) different, suggesting that permanent removal of nitrogen varies spatially across the harbour, which can have important connotations for ecosystem management.

year: 2018

title: Agglomeration elasticities and firm heterogeneity

authors: Maré, David C.

subjects: agglomeration

abstract: This paper examines three key issues encountered when estimating the relationship between agglomeration and multi factor productivity ('agglomeration elasticities'): the sorting of heterogeneous firms, the convexity of agglomeration effects, and the challenges of identifying the impact of persistent spatial differences in effective density. We use a firm-level panel containing production data together with detailed information on the geographic location of employment, covering a high proportion of the New Zealand economy. We are able to control for heterogeneity along firm, region, and industry dimensions, and to estimate separate agglomeration elasticities across industries and regions. Sorting leads to upward biased elasticity estimates but using firm fixed effects can lead to downward bias due to the highly persistent nature of agglomeration variables. Our preferred estimates control for sorting across regions and industries. Overall, we find a positive agglomeration elasticity of 0.066. Within industries and, to a lesser extent within regions, there is pronounced variation in the strength of agglomeration effects, and evidence of decreasing returns to agglomeration. High density areas attract firms that benefit most from agglomeration.

text: Agglomeration elasticities and firm heterogeneity This paper examines three key issues encountered when estimating the relationship between agglomeration and multi factor productivity ('agglomeration elasticities'): the sorting of heterogeneous firms, the convexity of agglomeration effects, and the challenges of identifying the impact of persistent spatial differences in effective density. We use a firm-level panel containing production data together with detailed information on the geographic location of employment, covering a high proportion of the New Zealand economy. We are able to control for heterogeneity along firm, region, and industry dimensions, and to estimate separate agglomeration elasticities across industries and regions. Sorting leads to upward biased elasticity estimates but using firm fixed effects can lead to downward bias due to the highly persistent nature of agglomeration variables. Our preferred estimates control for sorting across regions and industries. Overall, we find a positive agglomeration elasticity of 0.066. Within industries and, to a lesser extent within regions, there is pronounced variation in the strength of agglomeration effects, and evidence of decreasing returns to agglomeration. High density areas attract firms that benefit most from agglomeration.

year: 2013

title: Keynote address: Is there a distinctive Māori psychology?

authors: Durie, Mason

subjects: Maori

abstract: Many of the theoretical paradigms that underpin the study of psychology pay marginal attention to culture as a determinant of psychology.
While there are some aspects of human experience that are universal, patterns of thinking, feeling and behaving are by no means divorced from specific cultural influence. A challenge for Māori psychologists is to re-examine psychological theory from a Māori perspective. In attempting to identify the psychological distinctiveness underlying a Māori perspective, this paper has introduced marae encounters as a rich source of information within which distinctive psychological characteristics can be identified.

text: Keynote address: Is there a distinctive Māori psychology? Many of the theoretical paradigms that underpin the study of psychology pay marginal attention to culture as a determinant of psychology.
While there are some aspects of human experience that are universal, patterns of thinking, feeling and behaving are by no means divorced from specific cultural influence. A challenge for Māori psychologists is to re-examine psychological theory from a Māori perspective. In attempting to identify the psychological distinctiveness underlying a Māori perspective, this paper has introduced marae encounters as a rich source of information within which distinctive psychological characteristics can be identified.

year: 2003