Responses of floodplain birds to high-amplitude precipitation fluctuations over two decades
- Authors: Reid, Tim , Lada, Hania , Selwood, Katherine , Horrocks, Gregory , Thomson, James , Mac Nally, Ralph
- Date: 2022
- Type: Text , Journal article
- Relation: Austral Ecology Vol. 47, no. 4 (2022), p. 828-840
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- Description: Globally, high-amplitude variation in weather (e.g. precipitation) is increasing in frequency and magnitude. This appears to be so for the southern Murray-Darling Basin, Australia, where droughts of unprecedented (in the instrumental record, extending back to the mid-1800s) depth and duration (1997–first half of 2010; second half of 2012–) are being punctuated by extreme wet periods, albeit of shorter duration (‘Big Wet’, second half of 2010–first half of 2012). We have previously reported on the responses of floodplain-forest birds to the cessation of the longest recorded drought (‘Big Dry’, 1997–first half of 2010), but we found little evidence of a rebound, at least shortly after the Big Wet. However, we reasoned that there may have been insufficient time for the birds to have responded in that short time, so we repeated the survey program 5 years after the end of the Big Wet (2017). Bird occurrences, reproductive activity and success were substantially greater compared with late in the Big Dry (2009) than they had been soon after the Big Wet (2013). However, bird occurrences still fell well below measurements in the early-Big Dry (1998), so that the avifauna appears to be in decline, most probably because the length of drought periods far exceeds that of wet periods giving the birds too little time to recover fully. © 2022 The Authors. Austral Ecology published by John Wiley & Sons Australia, Ltd on behalf of Ecological Society of Australia.
Bird responses to riparian management of degraded lowland streams in southeastern Australia
- Authors: Hale, Robin , Reich, Paul , Johnson, Matthew , Hansen, Birgita , Lake, Philip , Thomson, James , Mac Nally, Ralph
- Date: 2015
- Type: Text , Journal article
- Relation: Restoration Ecology Vol. 23, no. 2 (2015), p. 104-112
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- Description: We assessed the degree to which fencing, livestock exclusion, and replanting of riparian zones affected avian assemblages in massively cleared landscapes. Measurements were made at three creeks in the southern Murray-Darling Basin in southeastern Australia, each of which had circa 1-km long treated sections and paired "untreated" circa 1-km sections, where no fencing, planting, or stock exclusion was done. We measured the change in vegetation characteristics and abundances of native birds for up to 8 years after works were completed. Prior to data collection, we developed expected responses of bird species based on the anticipated time-courses of change in vegetation structure. We used hierarchical Bayesian models to explore the effects of the management actions, and to account for within-site variation in vegetation characteristics. There were major changes in vegetation structure (reductions in bare ground and increases in shrubs and tree recruitment) but avian responses generally were small and not as expected. There are at least four possible reasons for the limited avian responses: (1) there has been a long-term decline in woodland birds across the region; (2) the study was conducted during the longest drought in the instrumental record in the study region; (3) the total amount of replanted vegetation was small in a massively denuded region; and (4) monitoring may have been over too short a term to detect responses to longer-term changes in structural vegetation. © 2014 Society for Ecological Restoration.
Climate drying amplifies the effects of land-use change and interspecific interactions on birds
- Authors: Bennett, Joanne , Clarke, Rohan , Horrocks, Gregory , Thomson, James , Mac Nally, Ralph
- Date: 2015
- Type: Text , Journal article
- Relation: Landscape Ecology Vol. 30, no. 10 (2015), p. 2031-2043
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- Description: Context: Climate change may amplify the effects of land-use change, including induced changes in interspecific interactions. Objectives: To investigate whether an avifauna changed over a period of severe drought, and if changes in avifaunas were related to changes in vegetation characteristics and the irruption of a despotic native species, the noisy miner Manorina melanocephala. Methods: In the box–ironbark forests of south-eastern Australia, we resurveyed the avifaunas and remeasured vegetation characteristics in 120 forest transects in 2010–2011 that had previously been measured in 1995–1997. Results: The avifauna changed markedly over the prolonged drought, and changes were more marked in smaller fragments of remnant vegetation in which more pronounced vegetation change had occurred. The noisy miner increased differentially in smaller remnants adding to the declines, especially for small-bodied birds. Conclusions: Long droughts interspersed with short wet periods are projected for the region, so the imposition of climate effects on an already much-modified region has profound implications for the avifauna. The noisy miner has (and continues) to benefit from both land-use and climate change, so future sequences of drought interspersed with short wet periods are likely to lead to further changes in the avifauna as the miner extends its occupancy. Differential reductions in small nectarivores and insectivores will affect ecosystem processes, including the control of defoliating insects, seed dispersal and pollination. © 2015, Springer Science+Business Media Dordrecht.
Regime shifts, thresholds and multiple stable states in freshwater ecosystems; a critical appraisal of the evidence
- Authors: Capon, Samantha , Lynch, Jasmyn , Bond, Nick , Chessman, Bruce , Davis, Jenny , Davidson, Nick , Finlayson, C. Max , Gell, Peter , Hohnberg, David , Humphrey, Chris , Kingsford, Richard , Nielsen, Daryl , Thomson, James , Ward, Keith , Mac Nally, Ralph
- Date: 2015
- Type: Text , Journal article
- Relation: Science of the Total Environment Vol. , no. (2015), p.
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- Description: The concepts of ecosystem regime shifts, thresholds and alternative or multiple stable states are used extensively in the ecological and environmental management literature. When applied to aquatic ecosystems, these terms are used inconsistently reflecting differing levels of supporting evidence among ecosystem types. Although many aquatic ecosystems around the world have become degraded, the magnitude and causes of changes, relative to the range of historical variability, are poorly known. A working group supported by the Australian Centre for Ecological Analysis and Synthesis (ACEAS) reviewed 135 papers on freshwater ecosystems to assess the evidence for pressure-induced non-linear changes in freshwater ecosystems; these papers used terms indicating sudden and non-linear change in their titles and key words, and so was a positively biased sample. We scrutinized papers for study context and methods, ecosystem characteristics and focus, types of pressures and ecological responses considered, and the type of change reported (i.e., gradual, non-linear, hysteretic or irreversible change). There was little empirical evidence for regime shifts and changes between multiple or alternative stable states in these studies although some shifts between turbid phytoplankton-dominated states and clear-water, macrophyte-dominated states were reported in shallow lakes in temperate climates. We found limited understanding of the subtleties of the relevant theoretical concepts and encountered few mechanistic studies that investigated or identified cause-and-effect relationships between ecological responses and nominal pressures. Our results mirror those of reviews for estuarine, nearshore and marine aquatic ecosystems, demonstrating that although the concepts of regime shifts and alternative stable states have become prominent in the scientific and management literature, their empirical underpinning is weak outside of a specific environmental setting. The application of these concepts in future research and management applications should include evidence on the mechanistic links between pressures and consequent ecological change. Explicit consideration should also be given to whether observed temporal dynamics represent variation along a continuum rather than categorically different states.
Floodplain ants show a stronger response to an extensive flood than to variations in fallen-timber load
- Authors: Horrocks, Gregory , Cunningham, Shaun , O'Dowd, Dennis , Thomson, James , Mac Nally, Ralph
- Date: 2012
- Type: Text , Journal article
- Relation: Austral Ecology Vol. 37, no. 4 (2012), p. 518-528
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- Description: Understanding how species respond to differences in resource availability is critical to managing biodiversity under the increasing pressures associated with climate change and growing human populations. Over the last century, the floodplain forests of Australia's largest river system, the Murray-Darling Basin, have been much affected by intensive harvesting of timber and firewood, and increasingly stressed by river regulation and, recently, an extended drought. Fallen timber - logs and shed branches - is known to play a key role in the ecology of several important species on these floodplains. Here, we monitored the response of the ant assemblages of a floodplain forest along the Murray River to a large-scale (34ha) experimental manipulation of fallen-timber load (0 to 80tha -1) over 4years. The forest was subjected to an incidental, extensive flood that enabled us to examine how two important stressors (timber removal and river regulation) affect ant assemblages. Ants showed little response to the proximity of fallen timber within plots, prior to the flood, or to different loads among plots, unlike other floodplain biota. After the flood, both ant abundance and species richness increased and species composition changed. However, this increase in species richness after flooding was less pronounced in plots with higher amounts of fallen timber. Managing river red gum forest using a mosaic of flood regimes, more representative of historical conditions, is likely to be the most effective way to maintain and enhance the diversity of ants and other biota on these important floodplains. © 2011 The Authors. Austral Ecology © 2011 Ecological Society of Australia.