• Energy Research

Effects of anthropogenic and environmental stressors on freshwater communities can propagate to ecosystem functions and may in turn impede ecosystem services. We investigated potential shifts in ecosystem functions that provide energy for freshwater ecosystems due to pesticides and salinity in 24 sites in streams of southeast Australia. First, effects on allochthonous organic matter (AOM) breakdown using three different substrates (leaves, cotton strips, wood sticks) in coarse and fine bags were investigated. Second, we examined effects on stream metabolism that delivers information on the ecosystem functions of gross primary production and ecosystem respiration. We found up to a fourfold reduction in AOM breakdown due to exposure to pesticides and salinity, where both stressors contributed approximately equally to the reduction. The effect was additive as, no interaction or correlation between the two stressors was found. Leaf breakdown responded strongly and exclusively to exposure to pesticides and salinity, whereas cotton strip breakdown was less sensitive and responded also to other stressors such as nutrients. No functional redundancy for the effects of pesticides and salinity on leaf breakdown was observed. For wood stick breakdown, no relationship to environmental gradients was found, however, the sample size was lower. We did not detect effects of pesticides or salinity on gross primary production or ecosystem respiration. A reduction in AOM breakdown by pesticides and salinity may impair the ecosystem services of food provision and possibly water purification. Hence, future studies should examine the spatial extent of these effects.

Effects of anthropogenic and environmental stressors on freshwater communities can propagate to ecosystem functions and may in turn impede ecosystem services. We investigated potential shifts in ecosystem functions that provide energy for freshwater ecosystems due to pesticides and salinity in 24 sites in streams of southeast Australia. First, effects on allochthonous organic matter (AOM) breakdown using three different substrates (leaves, cotton strips, wood sticks) in coarse and fine bags were investigated. Second, we examined effects on stream metabolism that delivers information on the ecosystem functions of gross primary production and ecosystem respiration. We found up to a fourfold reduction in AOM breakdown due to exposure to pesticides and salinity, where both stressors contributed approximately equally to the reduction. The effect was additive as, no interaction or correlation between the two stressors was found. Leaf breakdown responded strongly and exclusively to exposure to pesticides and salinity, whereas cotton strip breakdown was less sensitive and responded also to other stressors such as nutrients. No functional redundancy for the effects of pesticides and salinity on leaf breakdown was observed. For wood stick breakdown, no relationship to environmental gradients was found, however, the sample size was lower. We did not detect effects of pesticides or salinity on gross primary production or ecosystem respiration. A reduction in AOM breakdown by pesticides and salinity may impair the ecosystem services of food provision and possibly water purification. Hence, future studies should examine the spatial extent of these effects.

Secondary salinisation of rivers and streams is a global and growing threat that might be amplified by climate change. It can have many different causes, like irrigation, mining activity or the use of salts as de-icing agents for roads. Freshwater organisms only tolerate certain ranges of water salinity. Therefore secondary salinisation has an impact at the individual, population, community and ecosystem levels, which ultimately leads to a reduction in aquatic biodiversity and compromises the goods and services that rivers and streams provide. Management of secondary salinization should be directed towards integrated catchment strategies (e.g. benefiting from the dilution capacity of the rivers) and identifying threshold salt concentrations to preserve the ecosystem integrity. Future research on the interaction of salinity with other stressors and the impact of salinization on trophic interactions and ecosystem properties is needed and the implications of this issue for human society need to be seriously considered.

Secondary salinisation of rivers and streams is a global and growing threat that might be amplified by climate change. It can have many different causes, like irrigation, mining activity or the use of salts as de-icing agents for roads. Freshwater organisms only tolerate certain ranges of water salinity. Therefore secondary salinisation has an impact at the individual, population, community and ecosystem levels, which ultimately leads to a reduction in aquatic biodiversity and compromises the goods and services that rivers and streams provide. Management of secondary salinization should be directed towards integrated catchment strategies (e.g. benefiting from the dilution capacity of the rivers) and identifying threshold salt concentrations to preserve the ecosystem integrity. Future research on the interaction of salinity with other stressors and the impact of salinization on trophic interactions and ecosystem properties is needed and the implications of this issue for human society need to be seriously considered.

# The thermal breadth of temperate and tropical freshwater insects supports the climate variability hypothesis [https://doi.org/10.5061/dryad.9cnp5hqs1](https://doi.org/10.5061/dryad.9cnp5hqs1) **Primary article citation:** Dewenter, B. S., et al. (2024). "The thermal breadth of temperate and tropical freshwater insects supports the climate variability hypothesis." Ecology and Evolution 14(2): e10937. DOI: 10.1002/ece3.10937. **Overview:** The data consists of three thermal traits: critical thermal maximum (CTmax), critical thermal minimum (CTmin), and thermal breadth (TB) of freshwater insect species from two elevation gradients in temperate eastern Australia (southern New South Wales, NSW) and tropical eastern Australia (northern Queensland, QLD). Also included are the associated measures of the thermal regimes at the sites where the freshwater insects were collected. TB = CTmax - CTmin. Also reported are the size of the insects in terms of their head width (mm) and their taxonomy, the site collected from, and its elevation (m above sea level (asl)). ## Description of the data and file structure The variables in the dataset are described in the following table. The locations of the sites (and site information) are given in a second data set (see below). All measures of temperature or thermal traits are in degrees C. Head width refers to the width of the head of the individual insects at their widest point (in mm). NA = no observation (i.e., missing data) and does not imply 0. | Variable | Type | Full description of the variable | | :--------------- | :------------ | :------------------------------------------------------------------------------------------------------------ | | location | Site info | Location of the site either NSW (New South Wales) or QLD (Queensland) both in Australia | | Climate | Site info | Climate of the site either Temperate or Tropical | | elev | Site info | Elevation of the site (m asl) | | Order | Taxonomy | Order of the insect E (Ephemeroptera or mayflies) P (Plecoptera or stoneflies) T (Trichoptera or caddisflies) | | family | Taxonomy | Family of the inset | | genus | Taxonomy | Genus of the insect | | species | Taxonomy | Genus and species of the insect | | n\_CTmin | Thermal trait | Number of individuals that CTmin estimated from (min of 3) | | CTmin\_mean | Thermal trait | Mean estimate of CTmin | | CTmin\_sd | Thermal trait | Standard deviation of CTmin | | CTmin\_mean\_hw | Thermal trait | Mean head width (mm) of individuals that CTmin was estimated from | | CTmin\_sd\_hw | Thermal trait | Standard deviation of head width (mm) of individuals that CTmin was estimated from | | n\_CTmax | Thermal trait | Number of individuals that CTmax estimated from (min of 3) | | CTmax\_mean | Thermal trait | Mean estimate of CTmax | | CTmax\_sd | Thermal trait | Standard deviation of CTmax | | CTmax\_mean\_hw | Thermal trait | Mean head width (mm) of individuals that CTmax was estimated from | | CTmax\_sd\_hw | Thermal trait | Standard deviation of head width (mm) of individuals that CTmax was estimated from | | n\_TB | Thermal trait | Number of individuals that TB estimated from (min of 3) | | TB | Thermal trait | Mean estimate of TB | | TB\_sd | Thermal trait | Standard deviation of TB | | TB\_mean\_hw | Thermal trait | Mean head width (mm) of individuals that TB was estimated from | | TB\_mean\_hw\_sd | Thermal trait | Standard deviation of head width (mm) of individuals that TB was estimated from | A second data files contains the locations of the sites were the species were collected from for determining CTmin, CTmax and TB. This dataset also contains information about the thermal environment of these sites, recorded from data loggers measuring water temperature every 15 min, water quality (chemistry) and habitat. Where water quality variables were below detection limit, they are recorded as 0. Blank cells indicate no data. | Sample Sites | Climate | Either Temperate (for sites in NSW) or Tropical (for sites in QLD) | | :---------------------------------- | :----------------------------------------------------------------------- | :----------------------------------------------------------------- | | Stream | Name of the steam where collections made | | | Catchment | Catchment of the stream, Sn=Snowy River, Mu=Murry River, Ba=Barron River | | | Latitude | Latitude (S) of the site | | | Longitude | Longitude (E) of the site | | | Elevation (m) | Elevation of the site in m above sea level | | | Note | Notes about missing temperature data | | | Barometric Pressure (mm Hg) | Air pressure at the site (when dissolved oxygen measured) | | | 365 days | Annual minimum (°C) | Minimum temperature over a 365 day period | | Annual maximum (°C) | Maximum temperature over a 365 day period | | | Annual temperature range(°C) | Temperature range over a 365 day period | | | Annual mean (°C) | Mean temperature over a 365 day period | | | sd | Temperature standard deviation over a 365 day period | | | Mean diel variability per year (°C) | Mean diel temperature range over a 365 day period | | | sd | Standard elevation temperature diel range over a 365 day period | | | Sampling season | Season | Season Au= autumn, Dr=dry | | Seasonal temperature range (°C) | Temperature range over this season | | | Water Quality | Alkalinity (mg/L) | Alkalinity | | Nitrite (mg/L) | Nitrite | | | Total Phosphorus (mg/L) | Total P | | | Nitrogen Ammonia (mg/L) | Ammonia | | | Nitrate (mg/L) | Nitrate | | | Conductivity (mS/cm) | Electrical conductivity at 25°C | | | pH | pH | | | Dissolved Oxygen (% sat) | Dissolved oxygen | | | Turbidity (NTU) | Turbidity | | | Habitat | Velocity (m/s on bottom of stream) | Water velocity | | Stream depth (cm) | Water depth | | ## Sharing/Access information NA Climate change involves increases in mean temperature and changes in temperature variability at multiple temporal scales but research rarely considers these temporal scales. The Climate Variability Hypothesis (CVH) provides a conceptual framework for exploring the potential effects of annual scale thermal variability across climatic zones. The CVH predicts ectotherms in temperate regions tolerate a wider range of temperatures than those in tropical regions in response to greater annual variability in temperate regions. However, various other aspects of thermal regimes (e.g., diel variability), organisms’ size, and taxonomic identity are also hypothesised to influence thermal tolerance. Indeed, high temperatures in the tropics have been proposed as constraining organisms’ ability to tolerate a wide range of temperatures, implying that high annual maximum temperatures would be associated with tolerating a narrow range of temperatures. We measured thermal regimes and critical thermal limits (CTmax and CTmin) of freshwater insects in the orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) along elevation gradients in streams in temperate and tropical regions of eastern Australia and tested the CVH by determining which variables were most correlated with thermal breadth (Tbr = CTmax - CTmin). Consistent with the CVH, Tbr tended to increase with increasing annual temperature range. Tbr also increased with body size and Tbr was generally wider in Plecoptera than in Ephemeroptera or Trichoptera. We also find some support for a related hypothesis, the Climate Extreme Hypothesis (CEH), particularly for predicting upper thermal limits. We found no evidence that higher annual maximum temperature constrained individuals’ abilities to tolerate a wide range of temperatures. The support for the CVH we document, suggests that temperate organisms may be able to tolerate wider ranges of temperatures than tropical organisms. There is an urgent need to investigate other aspects of thermal regimes, such as diel temperature cycling and minimum temperature.

# The thermal breadth of temperate and tropical freshwater insects supports the climate variability hypothesis [https://doi.org/10.5061/dryad.9cnp5hqs1](https://doi.org/10.5061/dryad.9cnp5hqs1) **Primary article citation:** Dewenter, B. S., et al. (2024). "The thermal breadth of temperate and tropical freshwater insects supports the climate variability hypothesis." Ecology and Evolution 14(2): e10937. DOI: 10.1002/ece3.10937. **Overview:** The data consists of three thermal traits: critical thermal maximum (CTmax), critical thermal minimum (CTmin), and thermal breadth (TB) of freshwater insect species from two elevation gradients in temperate eastern Australia (southern New South Wales, NSW) and tropical eastern Australia (northern Queensland, QLD). Also included are the associated measures of the thermal regimes at the sites where the freshwater insects were collected. TB = CTmax - CTmin. Also reported are the size of the insects in terms of their head width (mm) and their taxonomy, the site collected from, and its elevation (m above sea level (asl)). ## Description of the data and file structure The variables in the dataset are described in the following table. The locations of the sites (and site information) are given in a second data set (see below). All measures of temperature or thermal traits are in degrees C. Head width refers to the width of the head of the individual insects at their widest point (in mm). NA = no observation (i.e., missing data) and does not imply 0. | Variable | Type | Full description of the variable | | :--------------- | :------------ | :------------------------------------------------------------------------------------------------------------ | | location | Site info | Location of the site either NSW (New South Wales) or QLD (Queensland) both in Australia | | Climate | Site info | Climate of the site either Temperate or Tropical | | elev | Site info | Elevation of the site (m asl) | | Order | Taxonomy | Order of the insect E (Ephemeroptera or mayflies) P (Plecoptera or stoneflies) T (Trichoptera or caddisflies) | | family | Taxonomy | Family of the inset | | genus | Taxonomy | Genus of the insect | | species | Taxonomy | Genus and species of the insect | | n\_CTmin | Thermal trait | Number of individuals that CTmin estimated from (min of 3) | | CTmin\_mean | Thermal trait | Mean estimate of CTmin | | CTmin\_sd | Thermal trait | Standard deviation of CTmin | | CTmin\_mean\_hw | Thermal trait | Mean head width (mm) of individuals that CTmin was estimated from | | CTmin\_sd\_hw | Thermal trait | Standard deviation of head width (mm) of individuals that CTmin was estimated from | | n\_CTmax | Thermal trait | Number of individuals that CTmax estimated from (min of 3) | | CTmax\_mean | Thermal trait | Mean estimate of CTmax | | CTmax\_sd | Thermal trait | Standard deviation of CTmax | | CTmax\_mean\_hw | Thermal trait | Mean head width (mm) of individuals that CTmax was estimated from | | CTmax\_sd\_hw | Thermal trait | Standard deviation of head width (mm) of individuals that CTmax was estimated from | | n\_TB | Thermal trait | Number of individuals that TB estimated from (min of 3) | | TB | Thermal trait | Mean estimate of TB | | TB\_sd | Thermal trait | Standard deviation of TB | | TB\_mean\_hw | Thermal trait | Mean head width (mm) of individuals that TB was estimated from | | TB\_mean\_hw\_sd | Thermal trait | Standard deviation of head width (mm) of individuals that TB was estimated from | A second data files contains the locations of the sites were the species were collected from for determining CTmin, CTmax and TB. This dataset also contains information about the thermal environment of these sites, recorded from data loggers measuring water temperature every 15 min, water quality (chemistry) and habitat. Where water quality variables were below detection limit, they are recorded as 0. Blank cells indicate no data. | Sample Sites | Climate | Either Temperate (for sites in NSW) or Tropical (for sites in QLD) | | :---------------------------------- | :----------------------------------------------------------------------- | :----------------------------------------------------------------- | | Stream | Name of the steam where collections made | | | Catchment | Catchment of the stream, Sn=Snowy River, Mu=Murry River, Ba=Barron River | | | Latitude | Latitude (S) of the site | | | Longitude | Longitude (E) of the site | | | Elevation (m) | Elevation of the site in m above sea level | | | Note | Notes about missing temperature data | | | Barometric Pressure (mm Hg) | Air pressure at the site (when dissolved oxygen measured) | | | 365 days | Annual minimum (°C) | Minimum temperature over a 365 day period | | Annual maximum (°C) | Maximum temperature over a 365 day period | | | Annual temperature range(°C) | Temperature range over a 365 day period | | | Annual mean (°C) | Mean temperature over a 365 day period | | | sd | Temperature standard deviation over a 365 day period | | | Mean diel variability per year (°C) | Mean diel temperature range over a 365 day period | | | sd | Standard elevation temperature diel range over a 365 day period | | | Sampling season | Season | Season Au= autumn, Dr=dry | | Seasonal temperature range (°C) | Temperature range over this season | | | Water Quality | Alkalinity (mg/L) | Alkalinity | | Nitrite (mg/L) | Nitrite | | | Total Phosphorus (mg/L) | Total P | | | Nitrogen Ammonia (mg/L) | Ammonia | | | Nitrate (mg/L) | Nitrate | | | Conductivity (mS/cm) | Electrical conductivity at 25°C | | | pH | pH | | | Dissolved Oxygen (% sat) | Dissolved oxygen | | | Turbidity (NTU) | Turbidity | | | Habitat | Velocity (m/s on bottom of stream) | Water velocity | | Stream depth (cm) | Water depth | | ## Sharing/Access information NA Climate change involves increases in mean temperature and changes in temperature variability at multiple temporal scales but research rarely considers these temporal scales. The Climate Variability Hypothesis (CVH) provides a conceptual framework for exploring the potential effects of annual scale thermal variability across climatic zones. The CVH predicts ectotherms in temperate regions tolerate a wider range of temperatures than those in tropical regions in response to greater annual variability in temperate regions. However, various other aspects of thermal regimes (e.g., diel variability), organisms’ size, and taxonomic identity are also hypothesised to influence thermal tolerance. Indeed, high temperatures in the tropics have been proposed as constraining organisms’ ability to tolerate a wide range of temperatures, implying that high annual maximum temperatures would be associated with tolerating a narrow range of temperatures. We measured thermal regimes and critical thermal limits (CTmax and CTmin) of freshwater insects in the orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) along elevation gradients in streams in temperate and tropical regions of eastern Australia and tested the CVH by determining which variables were most correlated with thermal breadth (Tbr = CTmax - CTmin). Consistent with the CVH, Tbr tended to increase with increasing annual temperature range. Tbr also increased with body size and Tbr was generally wider in Plecoptera than in Ephemeroptera or Trichoptera. We also find some support for a related hypothesis, the Climate Extreme Hypothesis (CEH), particularly for predicting upper thermal limits. We found no evidence that higher annual maximum temperature constrained individuals’ abilities to tolerate a wide range of temperatures. The support for the CVH we document, suggests that temperate organisms may be able to tolerate wider ranges of temperatures than tropical organisms. There is an urgent need to investigate other aspects of thermal regimes, such as diel temperature cycling and minimum temperature.