Nearshore movement ecology of a medium-bodied shark, the creek whaler Carcharhinus fitzroyensis

Background: The movement and habitat use patterns of medium-bodied nearshore sharks are poorly understood. However, these species face some of the highest levels of exposure to anthropogenic development. The habitat and space use strategies species exhibit affect their role within communities and how they respond to environmental change. The present study used passive acoustic telemetry to evaluate the residency, space use, and habitat use patterns of the creek whaler Carcharhinus fitzroyensis in a nearshore embayment in Queensland, Australia. Results: Individuals were monitored for approximately 18 months. Half of the monitored population were highly resident to the bay. In contrast, several individuals spent less than 2 weeks in the bay, suggesting that broader movements may occur in a portion of the population. Size had no effect on residency. Activity space size varied between months and time of day but was also not affected by animal size. All C. fitzroyensis spent the majority of time in seagrass habitat (70%) and deep water (>5 m) mud substrate (20%). Shallow mudflat, sandy inshore, and reef habitats were rarely used (7%). Although the sample size of immature individuals was relatively small, results indicated immature and mature C. fitzroyensis shared space and habitats. Conclusions: Overall, C. fitzroyensis used a combination of nearshore movement patterns typically exhibited by small- and large-bodied species. The movement patterns exhibited by C. fitzroyensis suggest that this species has a moderately high degree of seagrass habitat specialisation. Seagrass habitat is typically highly productive and may be an important foraging habitat for this species. Given the consistent use of seagrass habitat, C. fitzroyensis are likely vulnerable to population decline as a result of seagrass habitat loss. Future research should continue to investigate the unique movements of medium-bodied sharks

Effective ecosystem monitoring requires a multi-scaled approach

Ecosystem monitoring is fundamental to our understanding of how ecosystem change is impacting our natural resources and is vital for developing evidence-based policy and management. However, the different types of ecosystem monitoring, along with their recommended applications, are often poorly understood and contentious. Varying definitions and strict adherence to a specific monitoring type can inhibit effective ecosystem monitoring, leading to poor program development, implementation and outcomes. In an effort to develop a more consistent and clear understanding of ecosystem monitoring programs, we here review the main types of monitoring and recommend the widespread adoption of three classifications of monitoring, namely, targeted, surveillance and landscape monitoring. Landscape monitoring is conducted over large areas, provides spatial data, and enables questions relating to where and when ecosystem change is occurring to be addressed. Surveillance monitoring uses standardised field methods to inform on what is changing in our environments and the direction and magnitude of that change, whilst targeted monitoring is designed around testable hypotheses over defined areas and is the best approach for determining the causes of ecosystem change. The classification system is flexible and can incorporate different interests, objectives, targets and characteristics as well as different spatial scales and temporal frequencies, while also providing valuable structure and consistency across distinct ecosystem monitoring programs. To support our argument, we examine the ability of each monitoring type to inform on six key types of questions that are routinely posed for ecosystem monitoring programs, such as where and when change is occurring, what is the magnitude of change, and how can the change be managed? As we demonstrate, each type of ecosystem monitoring has its own strengths and weaknesses, which should be carefully considered relative to the desired results. Using this scheme, scientists and land managers can design programs best suited to their needs. Finally, we assert that for our most serious environmental challenges, it is essential that we include information from each of these monitoring scales to inform on all facets of ecosystem change, and this is best achieved through close collaboration between the scales. With a renewed understanding of the importance of each monitoring type, along with greater commitment to monitor cooperatively, we will be well placed to address some of our greatest environmental challenges

Evidence for inter- and intraspecific trophic niche separation among deepwater elasmobranchs on the southern Great Barrier Reef, Australia

Quantifying the trophic structure and interactions of deepwater (>200 m depth) elasmobranch assemblages is required to improve our understanding of deepwater ecosystems and the impacts of increased deepwater exploitation. To this end, we investigated the trophic ecology of deepwater elasmobranchs on the Great Barrier Reef (GBR) using a stable isotope (delta C-13 and delta N-15) approach. Our study included 4 species captured in the southern GBR deepwater eastern king prawn trawl fishery: the eastern spotted gummy shark Mustelus walkeri, the piked spurdog Squalus megalops, the pale spotted catshark Asymbolus pallidus, and the Argus skate Dentiraja polyommata. The delta C-13 and delta N-15 values of all 4 species ranged from -18.6 to -16.2 parts per thousand and 8.3 to 13.8 parts per thousand, respectively. The small C-13 range was likely due to the limited number of unique carbon baseline sources typically found in deepwater environments. Despite this, 3 of the 4 species exhibited relatively low core (40% SEA b ) isotopic niche overlap (<1 to 44%). Isotopic niche separation may be driven by multiple interacting factors including morphology, feeding strategies, or resource partitioning to reduce competition. Isotope analysis also provided evidence for intraspecific variation; S. megalops, D. polyommata and M. walked exhibited significant increases in delta N-15 (similar to 3 parts per thousand) and delta C-13 (similar to 2 parts per thousand) with size. Latitude, longitude, and depth had statistically significant but comparatively minor effects on isotope values (<= 1 parts per thousand) of the 4 species. Cumulatively, our results indicate that isotopic variation among deepwater elasmobranchs on the GBR is principally driven by size and species-level differences in resource use

Geographic and temporal variation in the trophic ecology of a small-bodied shark: evidence of resilience to environmental change

Shark dietary patterns can determine how they will respond to changes in prey availability and biodiversity. Geographic variation in diet can also indicate if species have unique structuring roles or feeding strategies in different environments. Unfortunately, little is known about the diet of most shark species and how diet varies over time and space. This study used stable isotope analysis to assess the diet of the Australian sharpnose shark (Rhizoprionodon taylori). Plasma and muscle δ13C and δ15N of R. taylori were compared with δ13C and δ15N baselines from multiple embayments to determine the isotopic niche, trophic position, and benthic and pelagic contributions to diet over time and space. Overall, R. taylori had a wide trophic position range and consumed prey from benthic and pelagic sources. However, there was geographic and temporal variation in trophic position and benthic and pelagic contributions. These findings indicate R. taylori is a dietary generalist, but different populations may have unique effects on distinct ecosystems. Geographic variation in diet also suggests R. taylori may be adaptive to changes in prey availability

Alien plants alter the growth form ratio and structure of Australian grasslands

[Questions]: Niche complementarity is often invoked to explain co-existence between native and alien plant species in grasslands. However, positive correlations between native and alien plant diversity observed in recent studies could mask the displacement of particular native species and functional groups or the negative effects of particular alien species. We asked: do alien species alter the species composition or proportions of growth forms in grasslands? Do particular alien species decrease native plant diversity?. [Location]: South Australian grasslands. [Methods]: We performed RDA ordination on growth form abundances or Hellinger-transformed species abundances obtained from plot-based surveys, constrained by alien species richness and cumulative cover. Control variables (climate, soil, land use and geographic space) were partialled out. We related individual alien species abundances to native richness, diversity and cover. We tested for functional differences between coexisting growth forms using trait hypervolumes. Results: While alien richness and cover explained just 2% of variance in native species composition (control variables 17%), aliens explained 18% of variance in native growth form abundance (control variables 33%), and were associated with increased herb and grass cover. Few individual alien species were associated with strong negative or positive differences in native richness, diversity or cover: correlations followed a Gaussian distribution with near-zero mean. Trait hypervolumes differed between native and alien herbs with an overlap of 0.44, indicating substantial, but not complete, functional differences.[Conclusions]: Given environmental context, alien cover was a good predictor of native herb and grass abundance relative to woody growth forms, but not of species composition per se. While the direction of causality is equivocal, aliens may facilitate native grasses and herbs, and niche complementarity may be involved. Due to functional redundancy across the species pool, the resulting species composition appears to be spatially contingent. Importantly for management, we identify alien species associated with reduced native diversity.TRY is currently supported by DIVERSITAS/Future Earth and the German Centre for Integrative Biodiversity Research (iDiv) Halle‐Jena‐Leipzig. SPONFOREST (BiodivERsA3‐2015‐58, PCIN‐2016‐055), COMEDIAS FEDER/Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación (CGL2017‐83170‐R), and REMEDINAL (Comunidad de Madrid grant REMEDINAL TE‐CM S2018/EMT‐4338) supported IMF

Alien plants alter the growth form ratio and structure of Australian grasslands

[Questions]: Niche complementarity is often invoked to explain co-existence between native and alien plant species in grasslands. However, positive correlations between native and alien plant diversity observed in recent studies could mask the displacement of particular native species and functional groups or the negative effects of particular alien species. We asked: do alien species alter the species composition or proportions of growth forms in grasslands? Do particular alien species decrease native plant diversity?. [Location]: South Australian grasslands. [Methods]: We performed RDA ordination on growth form abundances or Hellinger-transformed species abundances obtained from plot-based surveys, constrained by alien species richness and cumulative cover. Control variables (climate, soil, land use and geographic space) were partialled out. We related individual alien species abundances to native richness, diversity and cover. We tested for functional differences between coexisting growth forms using trait hypervolumes. Results: While alien richness and cover explained just 2% of variance in native species composition (control variables 17%), aliens explained 18% of variance in native growth form abundance (control variables 33%), and were associated with increased herb and grass cover. Few individual alien species were associated with strong negative or positive differences in native richness, diversity or cover: correlations followed a Gaussian distribution with near-zero mean. Trait hypervolumes differed between native and alien herbs with an overlap of 0.44, indicating substantial, but not complete, functional differences.[Conclusions]: Given environmental context, alien cover was a good predictor of native herb and grass abundance relative to woody growth forms, but not of species composition per se. While the direction of causality is equivocal, aliens may facilitate native grasses and herbs, and niche complementarity may be involved. Due to functional redundancy across the species pool, the resulting species composition appears to be spatially contingent. Importantly for management, we identify alien species associated with reduced native diversity.TRY is currently supported by DIVERSITAS/Future Earth and the German Centre for Integrative Biodiversity Research (iDiv) Halle‐Jena‐Leipzig. SPONFOREST (BiodivERsA3‐2015‐58, PCIN‐2016‐055), COMEDIAS FEDER/Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación (CGL2017‐83170‐R), and REMEDINAL (Comunidad de Madrid grant REMEDINAL TE‐CM S2018/EMT‐4338) supported IMF

Effective ecosystem monitoring requires a multi-scaled approach

Ecosystem monitoring is fundamental to our understanding of how ecosystem change is impacting our natural resources and is vital for developing evidence-based policy and management. However, the different types of ecosystem monitoring, along with their recommended applications, are often poorly understood and contentious. Varying definitions and strict adherence to a specific monitoring type can inhibit effective ecosystem monitoring, leading to poor program development, implementation and outcomes. In an effort to develop a more consistent and clear understanding of ecosystem monitoring programs, we here review the main types of monitoring and recommend the widespread adoption of three classifications of monitoring, namely, targeted, surveillance and landscape monitoring. Landscape monitoring is conducted over large areas, provides spatial data, and enables questions relating to where and when ecosystem change is occurring to be addressed. Surveillance monitoring uses standardised field methods to inform on what is changing in our environments and the direction and magnitude of that change, whilst targeted monitoring is designed around testable hypotheses over defined areas and is the best approach for determining the causes of ecosystem change. The classification system is flexible and can incorporate different interests, objectives, targets and characteristics as well as different spatial scales and temporal frequencies, while also providing valuable structure and consistency across distinct ecosystem monitoring programs. To support our argument, we examine the ability of each monitoring type to inform on six key types of questions that are routinely posed for ecosystem monitoring programs, such as where and when change is occurring, what is the magnitude of change, and how can the change be managed? As we demonstrate, each type of ecosystem monitoring has its own strengths and weaknesses, which should be carefully considered relative to the desired results. Using this scheme, scientists and land managers can design programs best suited to their needs. Finally, we assert that for our most serious environmental challenges, it is essential that we include information from each of these monitoring scales to inform on all facets of ecosystem change, and this is best achieved through close collaboration between the scales. With a renewed understanding of the importance of each monitoring type, along with greater commitment to monitor cooperatively, we will be well placed to address some of our greatest environmental challenges