Plant families exhibit unique geographic trends in C4 richness and cover in Australia

Numerous studies have analysed the relationship between C4 plant cover and climate. However, few have examined how different C4 taxa vary in their response to climate, or how environmental factors alter C4:C3 abundance. Here we investigate (a) how proportional C4 plant cover and richness (relative to C3) responds to changes in climate and local environmental factors, and (b) if this response is consistent among families. Proportional cover and richness of C4 species were determined at 541 one-hectare plots across Australia for 14 families. C4 cover and richness of the most common and abundant families were regressed against climate and local parameters. C4 richness and cover in the monocot families Poaceae and Cyperaceae increased with latitude and were strongly positively correlated with January temperatures, however C4 Cyperaceae occupied a more restricted temperature range. Seasonal rainfall, soil pH, soil texture, and tree cover modified proportional C4 cover in both families. Eudicot families displayed considerable variation in C4 distribution patterns. Proportional C4 Euphorbiaceae richness and cover were negatively correlated with increased moisture availability (i.e. high rainfall and low aridity), indicating they were more common in dry environments. Proportional C4 Chenopodiaceae richness and cover were weakly correlated with climate and local environmental factors, including soil texture. However, the explanatory power of C4 Chenopodiaceae models were poor, suggesting none of the factors considered in this study strongly influenced Chenopodiaceae distribution. Proportional C4 richness and cover in Aizoaceae, Amaranthaceae, and Portulacaceae increased with latitude, suggesting C4 cover and richness in these families increased with temperature and summer rainfall, but sample size was insufficient for regression analysis. Results demonstrate the unique relationships between different C4 taxa and climate, and the significant modifying effects of environmental factors on C4 distribution. Our work also revealed C4 families will not exhibit similar responses to local perturbations or climate.Samantha E. M. MunroeID, Francesca A. McInerney, Greg R. Guerin, Jake W. Andrae, Nina WeltiID, Stefan Caddy-Retalic, Rachel Atkins, Ben Sparro

Environmental associations of abundance-weighted functional traits in Australian plant communities

Predictions of how vegetation responds to spatial and temporal differences in climate rely on established links with plant functional traits and vegetation types that can be encoded into Dynamic Global Vegetation Models. Individual traits have been linked to climate at species level and at community level within regions. However, a recent global assessment of aggregated community level traits found unexpectedly weak links with macroclimate, bringing into question broadscale trait–climate associations and implicating local-scale environmental differences in the filtering of communities. To further evaluate patterns in light of these somewhat contradictory results, we quantified the power of macro-environmental variables to explain aggregated plant community traits, taking advantage of new trait data for leaf area, plant height and seed mass combined with a national survey that records cover-abundance using consistent methods for a large number of plots across Australia. In contrast to the global study, we found that abundance-weighted community mean and variance of leaf area and maximum height were correlated with macroclimate. Height and leaf area were highest in wet (especially warm, wet) environments, with actual evapotranspiration explaining 30% of variation in leaf area and 26% in maximum height. Seed mass was weakly related to environment, with no variable explaining more than 5% of variance. Considering all three traits together in a redundancy analysis, the complete set of environmental variables explained 43% of variation in site-mean traits and 29% of within-site trait variance. While significant trait variation remains unexplained, the trait–environment relationships reported here suggest climatically-driven filtering plays a strong role in assembling these vegetation communities. Regional assessments using standardised species abundances can therefore be used to predict aspects of vegetation function. Our quantification of plant community trait patterns along macroclimatic gradients at continental scale thereby contributes a much-needed functional basis for Australian vegetation.Greg R. Guerin, Rachael V. Gallagher, Ian J. Wright, Samuel C. Andrew, Daniel S. Falster, Elizabeth Wenk, Samantha E.M. Munroe, Andrew J. Lowe, Ben Sparro

Defining shark ecological specialisation: concepts, context, and examples

Sharks are traditionally classified as generalists that use a diverse range of habitats and prey. While this is an accurate description of some species, sharks exhibit a range of resource use strategies that affect their influence on communities. These strategies also influence resilience in the face of environmental and anthropogenic effects. Identifying resource use patterns is critical to understanding sharks in aquatic environments. However, despite the rapid increase in studies focused on measuring the dietary and habitat selection patterns of sharks, discussion on how to define the ecological specialisation of sharks has been limited. This is an impediment to communication and research as definitions of specialisation and how to measure it vary based on context. This review presents a conceptual framework within which to define the specialisation of sharks that can be applied to different environmental scales and goals. We present examples of species with varying degrees of specialisation at large and small scales within the proposed context. The effects of specialisation on population stability are also briefly discussed. Specialists are more sensitive to environmental fluctuations and thus more susceptible to population depletion following environmental changes. Therefore identifying specialised species is key to understanding species vulnerabilities and advancing ecological discussions

Habitat and space use of an abundant nearshore shark, Rhizoprionodon taylori

Shark resource-use strategies affect how they will respond to changes within their environment and, as such, may be important to consider in conservation and management. Movement data on sharks that use nearshore areas is particularly valuable because these habitats are highly dynamic. The present study used passive acoustic telemetry to examine the space-use, habitat-selection and habitat-specialisation patterns of the Australian sharpnose shark, Rhizoprionodon taylori, in a nearshore area. Habitat selectivity and specialisation were assessed across five benthic habitat types, including outer bay, seagrass, reef, sandy inshore and intertidal mudflats. The majority of R. taylori sharks were present for short periods of time, ranging from 1 to 112 days (mean ± s.e. = 16.9 ± 4.9). Activity-space analysis indicated that R. taylori roamed widely, but monthly activity-space size was consistent among individuals and through time. Both the population and individuals displayed wide habitat niches, indicating that the species may be resilient to environmental change. However, R. taylori consistently selected for seagrass over other habitats, potentially for feeding. Therefore, declines in seagrass availability may reduce R. taylori presence in nearshore areas and may be relevant to spatial management of this species

Variation in blacktip shark movement patterns in a tropical coastal bay

Comparisons between shark nursery populations are limited, however recent work has shown different populations exhibit distinct space use patterns. This study examined the residency and space use of young of the year (YOY) and juvenile Australian blacktip sharks, Carcharhinus tilstoni in a northern Australian nursery using acoustic telemetry. Presence and space use patterns exhibited by C. tilstoni were highly variable among individuals. In contrast to other shark nursery populations, the majority of YOY individuals left the nursery area within three months of release, while most juveniles exhibited long-term residency (6 months - 1 year). In addition, YOY individuals used smaller amounts of space than juveniles. Variable activity space size and location indicated individuals used different areas and often moved into new areas. High individual variation in juvenile populations is atypical for carcharhinid sharks, and contrasts with other nursery species, including the common blacktip shark C. limbatus, which are known to exhibit residency and consistent space use patterns in nursery areas. The unique patterns observed among C. tilstoni may be due to a number of factors, including differences in nursery habitat and population structure, or strategies to improve survival. This study highlights the importance of investigating nursery behaviour across different habitats and populations

Interspecific interactions, movement patterns and habitat use in a diverse coastal shark assemblage

Sharks are a highly diverse predatory taxon and are regularly found in large, potentially competitive, assemblages. However, the mechanisms that enable long-term coexistence and factors that drive complementary movement are poorly understood. As interspecific interactions can have a large influence on survival and trophic linkages, research on shark assemblages could substantially increase our understanding of marine community dynamics. In this study, we used passive acoustic telemetry to compare the activity space size, spatial overlap and habitat use patterns of six co-occurring shark species from the same family in a tropical nearshore embayment. Our results indicated that all sizes of Rhizoprionodon taylori (a small-bodied, highly productive species) used significantly larger amounts of space (e.g., mean 95% KUD = 85.9 km2) than juveniles of large-bodied, less productive species (e.g., Carcharhinus amboinensis; 62.3 km2) that use nearshore areas as nursery areas. Most large, less productive species appeared risk averse by using less space, while the smaller more productive species took greater risk by roaming broadly. These movement strategies are likely a means of avoiding predation or gaining access to new or additional resources. Spatial overlap patterns varied substantially between species with overlap in core use areas ranging from 1.2 to 27.6%, but were consistent over time. Most species exhibited low spatial overlap, suggesting spatial partitioning to reduce interspecific competition. While a few species exhibited a high degree of spatial overlap (up to 60% of activity space extent), dietary diversity may reduce competition to support co-occurrence. These data suggest that complex interactions occur in communal nurseries in nearshore waters where species are in direct competition for resources at vulnerable life stages.Michelle R. Heupel, Samantha E.M. Munroe, Elodie J.I. Lédée, Andrew Chin, Colin A. Simpfendorfe

Regional movement patterns of a small-bodied shark revealed by stable-isotope analysis

This study used stable-isotope analysis to define the nearshore regional residency and movements of the small-bodied Australian sharpnose shark Rhizoprionodon taylori. Plasma and muscle C-13 and N-15 of R. taylori were collected from across five embayments and compared with values of seagrass and plankton from each bay. Linear distances between adjacent bays ranged from 30 to 150 km. There was a positive geographic correlation between R. taylori tissue and environmental C-13 values. Populations with the highest tissue N-15 were collected from bays that had the highest environmental N-15 values. These results suggest that R. taylori did not forage more than 100 km away from their capture location within 6 months to 1 year. The successful application of isotope analysis to define R. taylori movement demonstrates that this technique may be used in addition to traditional methods to study the movement of sharks, even within similar habitats across regionally small spatial scales (<100 km)

Preservation quality of plant macrofossils through a Quaternary cave sediment sequence at Naracoorte, South Australia: Implications for vegetation reconstruction

Plant macrofossils are an important source for detailed vegetation reconstructions, often at the species level, which usually cannot be achieved with other plant material such as pollen and spores. However, the preservation quality of plant macrofossils is not well understood, especially in cave settings. Here, we assess the preservation quality of Quaternary plant macrofossils of Casuarinaceae, Astroloma humifusum, Banksia marginata and Eucalyptus species for Robertson Cave, in the World Heritage listed Naracoorte Caves. We conclude that the level of preservation varies considerably among taxa and plant organs, which can influence the vegetation reconstruction. Woody endocarps and fruits preserved better as macrofossils than leaves and flowers. The age of the sediment did not always impact the preservation quality, although in some cases it led to clear deterioration. The impact of fire was evident and possibly influenced the preservation potential of some taxa. Therefore, care must be taken when reconstructing vegetation from plant macrofossils as preservational changes and floristic change are sometimes difficult to separate.Rachel A. Atkins, Robert S. Hill, Kathryn E. Hill, Samantha E.M. Munroe, Elizabeth H. Ree

A vegetation carbon isoscape for Australia built by combining continental-scale field surveys with remote sensing

Published online: 5 July 2022Context: Maps of C3 and C4 plant abundance and stable carbon isotope values (δ13C) across terrestrial landscapes are valuable tools in ecology to investigate species distribution and carbon exchange. Australia has a predominance of C4- plants, thus monitoring change in C3: C4 cover and δ13C is essential to national management priorities. Objectives: We applied a novel combination of field surveys and remote sensing data to create maps of C3 and C4 abundance in Australia, and a vegetation δ13C isoscape for the continent. Methods: We used vegetation and land-use rasters to categorize grid-cells (1 ha) into woody ( C3), native herbaceous, and herbaceous cropland ( C3 and C4) cover. Field surveys and environmental factors were regressed to predict native C4 herbaceous cover. These layers were combined and a δ13C mixing model was used to calculate site-averaged δ13C values. Results: Seasonal rainfall, maximum summer temperature, and soil pH were the best predictors of C4 herbaceous cover. Comparisons between predicted and observed values at field sites indicated our approach reliably predicted generalised C3: C4 abundance. Southern Australia, which has cooler temperatures and winter rainfall, was dominated by C3 vegetation and low δ13C values. C4- dominated areas included northern savannahs and grasslands. Conclusions: Our isoscape approach is distinct because it incorporates remote sensing products that calculate cover beneath the canopy, the influence of local factors, and extensive validation, all of which are critical to accurate predictions. Our models can be used to predict C3: C4 abundance under climate change, which is expected to substantially alter current C3: C4 abundance patterns.Samantha E. M. Munroe, Greg R. Guerin, Francesca A. McInerney, Irene Martín, Forés, Nina Welti, Mark Farrell, Rachel Atkins, Ben Sparro

The photosynthetic pathways of plant species surveyed in Australia’s national terrestrial monitoring network

Published online: 01 April 2021The photosynthetic pathway of plants is a fundamental trait that influences terrestrial environments from the local to global level. The distribution of different photosynthetic pathways in Australia is expected to undergo a substantial shift due to climate change and rising atmospheric CO2; however, tracking change is hindered by a lack of data on the pathways of species, as well as their distribution and relative cover within plant communities. Here we present the photosynthetic pathways for 2428 species recorded across 541 plots surveyed by Australia’s Terrestrial Ecosystem Research Network (TERN) between 2011 and 2017. This dataset was created to facilitate research exploring trends in vegetation change across Australia. Species were assigned a photosynthetic pathway using published literature and stable carbon isotope analysis of bulk tissue. The photosynthetic pathway of species can be extracted from the dataset individually, or used in conjunction with vegetation surveys to study the occurrence and abundance of pathways across the continent. This dataset will be updated as TERN’s plot network expands and new information becomes available.Samantha E. M. Munroe, Francesca A. McInerney, Jake Andrae, Nina Welti, Greg R. Guerin, Emrys Leitch, Tony Hall, Steve Szarvas, Rachel Atkins, Stefan Caddy-Retalic, Ben Sparro