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Accueil du site → Doctorat → Australie → 2011 → Vegetation structure & food resources in drought affected semi-natural grasslands : Implications for the nationally vulnerable Plains-wanderer Pedionomus torquatus

Charles Sturt University (2011)

Vegetation structure & food resources in drought affected semi-natural grasslands : Implications for the nationally vulnerable Plains-wanderer Pedionomus torquatus

Eklom, Kylie

Titre : Vegetation structure & food resources in drought affected semi-natural grasslands : Implications for the nationally vulnerable Plains-wanderer Pedionomus torquatus

Auteur : Eklom, Kylie

Grade : Doctor of Philosophy (PhD) 2011

Université de soutenance : Charles Sturt University

Résumé
This thesis investigates the availability of invertebrate and seed food resources in grasslands used by the Plains-wanderer Pedionmus torquatus, a nationally vulnerable grassland bird endemic to Australia. While there is good knowledge about the relationship between vegetation structure and habitat suitability for Plains-wanderers, less is known about how food resources vary across grasslands of different structural suitability and how stock grazing impacts on food abundance. Also, the diet of the Plains-wanderer is relatively well known (comprising fallen seeds and invertebrates), but there is no information about the nutritional importance of seeds and invertebrates as sources of assimilated nutrients.The overall aim of this thesis is to investigate the relationship between vegetation structure, grazing and food resources and the nutritional importance of these food resources for Plains-wanderers in semi-natural grasslands. Plains-wanderers occurred in very low numbers throughout this study which prevented any direct work being carried out on the interaction between Plains-wanderers and food resources. Therefore, the approach used was to relate the projects’ research findings to current knowledge about Plains-wanderer ecology. The study was carried out during spring in 2006, 2007 and 2008 at Oolambeyan National Park (ONP) and surrounding pastoral properties in western NSW, Australia. In 2006, vegetation structure was measured, and seeds and invertebrates collected from three grassland types designated as primary, secondary and unsuitable grassland, occurring entirely within ONP. In 2007, the same information was collected from grasslands under two contrasting management regimes, conservation grazed grasslands on ONP and production grazed grasslands on neighbouring properties. Blood samples were collected from 14 Plains-wanderers during the spring of 2007 and 2008 for stable isotope analysis to determine the nutritional importance of seeds and invertebrates as sources of assimilated stable-carbon ( δ13C) and stable-nitrogen (δ15N).Following univariate and multivariate analyses, vegetation structure was found to be similar between primary and secondary grasslands, whereas unsuitable grassland comprised a thick layer of dead fallen rye grass. There was little difference in invertebrate abundance between grassland types, although there were almost twice as many seeds in unsuitable grassland than primary grassland. Despite substantial differences in vegetation structure between conservation and production grazed grasslands, the abundance of seeds and invertebrates varied little between these management types. To determine how invertebrate and seed abundance were related to vegetation structure, I modelled relationships using hierarchical generalized linear models. Overall there was a high level of uncertainty in predicting seed and invertebrate abundance based on vegetation structure alone. It is likely that extremely dry climatic conditions constrained invertebrate and seed abundance at the time of sampling, potentially reducing differences between grassland and management types.Finally, I examined the spatial pattern of seeds and invertebrates within each site to determine differences in the dispersion of food items (e.g. uniform or clumped), as this may have implications for Plains-wanderer foraging efficiency. Inverse distance weighting interpolation was used to map the predicted dispersion of these resources within each site. The Gini coefficient was used as a measure of evenness for each site. While some sites had a clumped dispersion of seeds, overall, seeds and invertebrates had a fairly uniform dispersion within sites regardless of grassland type or management regime. There was some evidence of a dietary shift in Plains- wanderers between years based on assimilated δ13C and δ15N ratios. A substantial shift in stable-carbon ratios suggests that carbon was being sourced from seeds of plants with a different photosynthetic pathway (C3 and C4) in different years, while nitrogen was sourced from invertebrates in 2007 and seeds in 2008. This indicates that Plains-wanderers may switch their diet based on food availability at the time and are thus dietary generalists.It is likely that the prolonged drought had a substantial impact on food resources, although comparative data from ‘wet’ years are required to substantiate this. The main conclusion from this study is that during drought, the abundance and dispersion of food resources did not vary substantially between grassland types or management types. This suggests that grassland suitability for Plains-wanderers is defined principally by vegetation structure during drought periods. It also suggests that regardless of the grazing intensity during drought, food resources are affected similarly owing to the over-riding influence of climate, but production grazing creates areas of grassland that are structurally too bare for Plains-wanderers

Subjects : Drought ; Food resources ; Grassland ; Invertebrates ; Pitfall, vaccum ; Plains-wanderer ; Seeds ; Vegetation structure

Présentation National Library of Australia

Page publiée le 20 mai 2012, mise à jour le 2 juin 2017