370 research outputs found
Modelling confinement experiments in community ecology: Differential mobility among competitors
No full textField experiments in which mobile organisms are confined inside enclosures have been widely used in many areas of marine, freshwater and terrestrial ecology in the past three decades. Some ecologists believe that at least some and possibly most, of the interpretation of this work may be subject to dispute because of potential artefacts associated with the confinement itself. Simulations suggested that moderate or even severe artefacts may arise from using enclosures that are ‘too small’, which could produce inferential nonsense in some circumstances (Mac Nally, 1997). Here, the influence of differential mobility is explicitly considered in a simulated environment, with organisms confined in enclosures of a variety of sizes. Some simulations involve single populations, while others pit together competitors differing only in mobility. Three foraging strategies based on simple movement principles are simulated. Results indicate that the relationships between resource consumption and mobility will depend upon foraging strategy, often in unexpected ways compared with the implications of spatial averaging. Outcomes of interactions among pairs of populations having the same foraging strategy but with different mobilities also are complex, indicating that the results of confinement experiments may involve non-intuitive interactions between mobility and foraging method. There needs to be a refocusing on basic biology of organisms used in confinement experiments (e.g. movement distributions) and, particularly, constructing defensible statements on why the selected scales were used
Catchment zoning for freshwater conservation: refining plans to enhance action on the ground
No full textSummary: Recent advances in freshwater conservation planning allow addressing some of the specific needs of these systems. These include spatial connectivity or propagation of threats along stream networks, essential to ensure the maintenance of ecosystem processes and the biodiversity they sustain. However, these peculiarities make conservation recommendations difficult to implement as they often require considering large areas that cannot be managed under conventional conservation schemes (e.g. strict protection). To facilitate the implementation of conservation in freshwater systems, a multizoning approach with different management zones subject to different management regimes was proposed. So far, this approach has only been used in post hoc exercises where zones were allocated using expert criteria. This might undermine the cost-effectiveness of conservation recommendations, because both the allocation and extent of these zones have never been optimized using the principles of systematic planning. Here, we demonstrate how to create a catchment multizone plan by using a commonly applied tool in marine and terrestrial realms. We first test the capability of Marxan with Zones to address problems in rivers by using a simulated example and then apply the findings to a real case in the Daly River catchment, northern Australia. We also demonstrate how to address common conservation planning issues, such as accounting for threats or species-specific connectivity needs in this multizone framework, and evaluate their effects on the spatial distribution and extent of different zones. We found that by prioritizing the allocation of zones subject to different management regimes, we could minimize the total area in need of strict conservation by a twofold factor. This reduction can be further reduced (threefold) when considering species' connectivity needs. The integration of threats helped reduce the average threats of areas selected by a twofold factor. Synthesis and applications. Catchment zoning can help refine conservation recommendations and enhance cost-effectiveness by prescribing different management regimes informed by ecological needs or distribution of threats. Reliable information on these factors is a key to ensure soundness of planning. Freely available software can be used to implement the approach we demonstrate here. Catchment zoning can help refine conservation recommendations and enhance cost-effectiveness by prescribing different management regimes informed by ecological needs or distribution of threats. Reliable information on these factors is a key to ensure soundness of planning. Freely available software can be used to implement the approach we demonstrate here
Do space-for-time assessments underestimate the impacts of logging on tropical biodiversity? : an Amazonian case study using dung beetles
No full textHuman alteration of the global environment is leading to a pervasive loss of biodiversity. Most studies evaluating human impacts on biodiversity occur after the disturbance has taken place using spatially distinct sites to determine the undisturbed reference condition. This approach is known as a space-for-time (SFT) substitution. However, SFT substitution could be underestimating biodiversity loss if spatial controls fail to provide adequate inferences about pre-disturbance conditions. We compare the SFT substitution with a before–after control–impact (BACI) approach by assessing dung beetles before and after a logging exploration in the Brazilian Amazon. We sampled 34 logging management units, of which 29 were selectively logged with different intensities after our first collection. We used dung beetle species richness, species composition and biomass as our biodiversity response metrics and the gradient of selective logging intensity as our explanatory metric. Only the BACI approach consistently demonstrated the negative impacts of logging intensification on all dung beetle community metrics. Moreover, the BACI approach explained significantly more of the variance in all the relationships and it doubled the estimates of species loss along the gradient of logging intensity when compared to SFT. Synthesis and applications. Our results suggest that space-for-time (SFT) substitution may greatly underestimate the consequences on local species diversity and community turnover. These results have important implications for researchers investigating human impacts on biodiversity. Incentivizing before–after control–impact (BACI) approaches will require longer-term funding to gather the data and stronger links between researchers and landowners. However, BACI approaches are accompanied by many logistical constraints, making the continued use of SFT studies inevitable in many cases. We highlight that non-significant results and weak effects should be viewed with caution
Birds, fruit and nectar: spatio-temporal patterns of regional bird abundance and food availability in subtropical eastern Australia
No full textSpatio-temporal patterns of animal abundance, and the factors explaining them, have seldom been studied at a regional scale. I sought to describe and explain patterns of bird abundance (for all birds, and for frugivores and nectarivores) by counting birds and measuring fruit and flower availability monthly for 24 months at 83 sites across a 300 000 ha region in subtropical eastern Australia. In particular, I wanted to examine the effects on abundance of climate, primary productivity, vegetation and food availability. Patterns of fruit availability were similar in both years, but the spatio-temporal pattern of flowering differed between years because of irregular blossoming by eucalypts. Most variation in fruit and flowers was spatial; spatio-temporal variation was also important, but there was relatively little temporal variation. Vegetation type and primary productivity were the greatest influences on fruit availability; flowering was chiefly influenced by primary productivity and rainfall. As with food availability, most variation in bird abundance was spatial: there were more birds in certain vegetation types and where mean food (fruit and flower) availability was higher. Spatio-temporal variation resulted from food tracking, whereby frugivores and nectarivores moved among localities and vegetation types in response to seasonal changes in the availability of fruit and flowers. However, spatio-temporal variation in consumer abundance was not as great as might have been expected, given the degree of spatio-temporal variation in food availability; this suggests that fruit and nectar were generally in over-supply during the study. Temporal variation in bird abundance was less marked than spatial or spatio-temporal variation, and was chiefly associated with variation in primary productivity, probably because recruitment of juveniles and influxes of migratory insectivores occurred during times of high productivity; there was little net migration into or out of the study region by frugivores or nectarivores. Of the explanatory factors I examined, food (fruit and flower) availability had the greatest influence on bird abundance. Because food availability differed among vegetation types, the association between vegetation and bird abundance was also strong. Although variables relating to primary productivity were important influences on food availability, they had only weak effects on bird abundance. The weakness of the productivity-abundance relationship was partly due to a combination of low spatial (but high temporal) variation in productivity and low temporal (but high spatial) variation in bird abundance. I would expect the relationship to be stronger in areas with greater spatial variation in productivity, or where long-distance migrants were a greater component of the avifauna. My study represents an important advance in our understanding of the factors that influence animal abundance over large areas. Abundance is strongly influenced by food availability, which is in turn affected by climate, primary productivity and vegetation characteristics. Seasonal changes in food availability drive intra-regional bird movements among vegetation types and localities; such movements need to be considered in conservation planning, which is often premised on species having static distributions
Impacts of multiple stressors on ecological dynamics of river red gum (Eucalyptus camaldulensis) Denhn. forests on the Murray River floodplain
No full textRiverine ecosystems already under stress from human actions, such as land-use change, river regulation and excessive surface and groundwater extraction, now are experiencing a profound, chronic, additional stress through climate change. Forest mortality, due to water extraction and salinization, is likely to be exacerbated by climate change-induced droughts. In south-eastern Australia, the extensive river red gum (Eucalyptus camaldulensis Dehnh.) forests provide one of the world’s most dramatic examples of forest dieback. Reduced water availability has created conditions that are unfavourable for the seedling regeneration and adult survival. I used 42-year tree growth dataset to examine the effects of initial stand density on mortality, tree growth and structure of floodplain forests. I showed that a dramatic increase in mortality in the high-density river red gum stands coincided with a steep temporal gradient of drying (imposed by a warming climate, river regulation and reduced groundwater availability), while mortality remained little changed in lower-density treatments. Lower-density planting also produced stands with higher median and maximum stem diameters than higher–density stands. Early thinning also had a pronounced effect on forest structure, tree growth, habitat quality and aboveground carbon (AGC) storage rates of river red gum stands on the eastern reaches of the Murray River floodplain. Thinning improved habitat value by producing hollow-bearing trees, while the unthinned treatment produced none. Moderately thinned stands had the highest aboveground carbon storage rate (4.1 t C yr-1) and the highest aboveground carbon stocks (200.2 ± 9.6 t C ha -1) after 42 years, while the unthinned treatment had the lowest carbon storage rate (1.6 t C yr-1) and an intermediate level of aboveground standing carbon (165.1 ± 31.1 t C ha-1). I showed that flooding and tree canopy cover affected the composition and native richness of understorey plant assemblages on semi-arid and temperate reaches of the Murray River. Sites with the highest canopy cover had the lowest native richness, whereas sites with low to intermediate canopy cover had the highest native species richness. Flooding more than doubled the predicted number of native species compared to unflooded sites. Seedling survival is likely to be a critical process limiting population viability of dominant floodplain tree species in many water-limited river basins. My survival experiment (including 960 planted seedlings) showed that flooding had a pronounced positive effect on regeneration, increasing survival by a factor of 8 (in the absence of livestock feral and native grazing). Grazing and sediment salinity had strong negative effects on seedling survival at both flooded and unflooded sites. Positive effects of flooding (on survival) largely were nullified by grazing and sediment salinity. My results highlight the importance of initial stand density and seedling survival as key determinants of the structural development of floodplain forests. Variation in flooding, grazing and sediment salinity are strong environmental filters, controlling short-term establishment and long-term population viability. Given the extensive dieback of mature trees from river regulation and salinization, there is an urgent need to enhance seedling regeneration, the future forest. Managing these filters correctly probably will enhance regeneration and structural development of floodplain forests. I recommend that environmental flooding and early thinning of developing stands be considered as part of a broader management strategy to enhance regeneration, carbon storage, wildlife habitat and plant-community diversity
Changes in forest-bird assemblage structure in response to multiple pressures: climate and vegetation change
No full textClimate change is linked to negative effects on vegetation, including drought-induced vegetation dieback. Large-scale dieback leads to considerable carbon emissions and loss of ecological resources for fauna. The consequences of vegetation change for biodiversity include; reductions in breeding success, population sizes, dispersal, resistance to other pressures, and changes in species composition. Changes in species composition alter interspecific interactions, such as competition, predation, parasitism and pollination, which collectively affect assemblage dynamics and ecosystem function. Competitive species that are resistant to, or have benefited from disturbances may monopolize resources (nesting sites and food) and limit the survival and recruitment of disturbance-sensitive species. I investigated whether and how the vegetation structure, composition and carbon content changed over a period of extended drought in a much-modified forest ecosystem. I explored if landscape configuration, management practice or soil type influenced vegetation change and identified the factors that influence the spatial and temporal distribution of bird assemblages, including climate, vegetation structure, vegetation loss/fragmentation, interspecific species interactions and resource provision. Lastly, I assessed if the recruitment of native birds is influenced by vegetation loss/fragmentation, drought-driven habitat degradation, and interspecific interactions. Box and ironbark forests of Victoria in south-eastern Australia are an example of a highly modified, ecosystem in which the joint effects of fragmentation and climate change have not been systematically measured. These forests experienced drought stress from 1997 until 2010, in conjunction with the on-going loss, degradation and fragmentation of native vegetation by human encroachment. The study design incorporates vegetation fragments of a range of sizes, allowing the evaluation of fragmentation/habitat loss effects. I made direct comparisons of changes in avian and vegetation assemblage structure and condition over the last 15 years by revisiting sites measured previously (1997). These data, used in conjunction with observations of breeding success, provided an opportunity to investigate the long-term interaction between vegetation change and climate-change. Forest structure was systemically different between the two periods. Canopy cover, shrub cover and litter decreased between 1997 and 2010, while the total basal area of dead trees in all size classes increased. The effects were amplified in fragmented vegetation, probably due to greater water and heat stress. Avian assemblages changed significantly between 1997 and 2010, with many woodland bird species halving in both prevalence (proportion of sites occupied) and abundance (numbers when present). Declines were largely independent of species ecological traits (i.e. nesting, foraging, range etc.). Changes in the bird community were associated with precipitation, temperature, vegetation cover (canopy, ground and mid-storey cover) and the density of the noisy miner Manorina melanocephala. The reduction in canopy foliage, ground-litter and shrub cover probably has reduced food resources and nesting sites. Greater noisy miner abundance as an additive effect of fragmentation and degradation had a greater negative effect on species’ breeding behavior than on-transect vegetation characteristics. Nectarivores tracked spatial and temporal variation in flowering, but this relationship was disrupted in the presence of noisy miners. The box-ironbark region serves as an exemplar for other regions undergoing increases in the frequency and duration of extreme climatic events, such as North America, Europe, southern Africa and Asia. My work is among the first to consider interacting pressures that arise from major drivers of ecological change. The loss, fragmentation and degradation of habitat have caused declines in many native species but have facilitated increases in the abundance and distribution of other native species. Projected climate change (i.e. hotter and drier conditions) may exacerbate changes in the bird assemblage by accelerating vegetation degradation, especially in smaller fragments. I found that greater drought-driven vegetation degradation in smaller fragments facilitated the expansion of a highly competitive native, the noisy miner. The noisy miner by acting as an interference competitor (defending space) disproportionately excluded smaller-bodied birds from sites where the noisy miner occurs. This reduced the access of small-bodied birds to valuable resources (nesting and food) which may limit their capacity to recover from adverse climate events (e.g. long drought), with long-term consequences for the persistence of small-bodied species. As climates become more extreme, similar effects to those that I report are likely to arise in other fragmented regions and for other taxa, because interspecific interactions are not limited to avifaunas, and fragmentation has been linked to altered species interactions in many regions of the world
Restoring connectivity: the effect of riparian replanting on in-stream organic carbon dynamics in a degraded agricultural landscape
No full textStreams and rivers are intrinsically linked to the terrestrial environment by the exchange of water, nutrients, organic matter and biota. Terrestrial-aquatic connectivity has been disrupted by the degradation and removal of riparian vegetation due to widespread agricultural development. Loss of terrestrial vegetation modifies channel shading, in-stream habitat, and the quantity and composition of organic carbon (i.e. energy) subsidies provided to stream food webs. Collectively, these changes result in biodiversity loss and altered ecosystem functioning. Replanting riparian vegetation aims to alleviate the adverse ecological effects of riparian clearance. Replanting is already commonly used for ecological restoration, but revegetation may become more widespread if restoration activities are driven by economic forces, such as payments for planting trees to mitigate climate change. However, replantings currently are often spatially limited and isolated, so the plantings may not have a large effect on halting or reversing ecological degradation. Riparian clearance and revegetation are likely to alter carbon dynamics, which is a critical process underpinning biodiversity and ecosystem functioning in streams. We have little knowledge of if, and when, riparian replanting will restore in-stream organic-carbon processes towards pre-clearance conditions, or of the broad-scale effects on carbon balances. The integration of aquatic fluxes into regional carbon budgets is an important component of regional, national and global carbon accounting. I sought to: (1) quantify the reach-scale effects of replanting on in-stream organic carbon dynamics; (2) assess the potential for organic matter properties to reflect the success of restoring terrestrial-aquatic connectivity; and (3) upscale organic carbon fluxes to project the consequences of revegetation for carbon balance and atmospheric feedback at watershed (= catchment) scales. I assessed the dynamics of aquatic organic carbon (input, standing stock, export and metabolism) in 15 streams (1st-3rd Strahler order) of an agricultural landscape in south-eastern Australia. Ten of the streams had reaches that were replanted with native woody vegetation 8 to 22 years prior to the study; I refer to these restored reaches as ‘replanted’ and other reaches in which there had been no plantings, pasture reaches, as ‘untreated’. Replanted stream reaches had greater inputs and accumulation of terrestrial organic carbon on the stream-bed than did untreated reaches. Replanting was correlated with a reduction in net ecosystem productivity and a shorter organic carbon turnover length. Within two decades of planting, metabolic rates in replanted reaches had values more typical of those in natural, forested streams, supporting the use of ecosystem metabolism as a functional indictor of restoration success at reach-scales. Metabolic measures could be combined with pattern-based measures, such as biodiversity, to demonstrate the ecological value of replanting. The export of organic carbon was governed by land-use and climatic variables at spatial scales larger than typical replanting projects. Watershed tree cover affected the composition of dissolved organic matter, but not its quantity. A greater proportion of the dissolved organic matter in agricultural streams was from within the stream and a reduced proportion was from terrestrial vegetation, compared to streams in forested watersheds. The characteristics of dissolved organic matter potentially provide an aggregate measure of aquatic and terrestrial connectivity over large spatial scales. The quantity of total organic carbon transported was controlled by discharge. Projected increases in rainfall variability will affect the timing and magnitude of storm-flows, altering the fluxes of energy subsidies among ecosystems in landscapes. The estimated organic carbon budget showed that replanted reaches potentially were a greater source of carbon than were untreated reaches (net change -0.52 g C m-2 day-1 ± 0.80 SD). At a watershed scale, this increased carbon loss per unit area of stream was small compared to organic carbon export from 3rd-order streams. Riparian restoration at reach spatial scales (i.e. 100s of m) can restore ecosystem processes towards pre-clearance condition, within two decades. However, the effects of replanting at small scales may be overwhelmed by changes to hydrologic processes arising from probable increased climate variability in the future. Addressing land-use effects requires a landscape perspective that incorporates spatial context and connectivity at multiple scales to guide restoration activities into the areas likely to provide the greatest ecological return for investment
Scale and an organism-centric focus for studying interspecific interactions in landscapes:Issues and Perspectives in Landscape Ecology
No full textMurray-Darling Basin Environmental Water Knowledge and Research Project: Waterbirds Theme Research Appendix
No full textAppendix 1 McGinness, H. M. (2016) Waterbird responses to flooding, stressors and threats. CSIRO, Australia. Technical literature review report. Appendix 2 McGinness, H.M., Langston, A., Robinson, F., Piper, M., Martin, J., Doerr, V.A.J., Kingsford, R., and Mac Nally, R. Satellite-tracking ibis and spoonbill movements and habitat choices. Appendix 3 McGinness, H.M., Robinson, F., Piper, M., and Hodgson, J., Kingsford, R., Mac Nally, R. and Doerr, V.A.J. Quantifying ibis and spoonbill egg and chick survival rates and mortality drivers using motion-sensing and time-lapse cameras. Appendix 4 Brandis, K., Bellio, M., Callaghan, D., Webster, E., Francis, R. Monitoring ibis and spoonbill nest success through on-ground tagged nest and water depth monitoring.Appendix 5 Brandis, K., McCann, J., Lyons, M. Ibis and spoonbill nest and colony mapping using drone imagery.Appendix 6 Ibis and spoonbill chick energy source assimilation. Current authors include: Paul McInerney, Kate Brandis, Heather McGinness, Ralph Mac Nally. Appendix 7 O’Brien, L. and McGinness, H.M. (in review) Ibis and spoonbill chick energy requirements: Implications for wetland management. Appendix 8 Lucy Wenger and Heather McGinness (2018) Waterbird Chick Development: A Visual Guide to Selected Australian Species. CSIRO, Australia. Appendix 9 Webster, E. (2017) Similarities and differences in breeding ecology of straw-necked ibis Threskiornis spinicollis and Australian white ibis T. moluccus in response to environmental flows. Honours thesis, UNSW. Appendix 10 Theme Data InventoryAppendix 11 Theme OutputsAppendix 12 Theme Engagement and Communications Activitie
- …
