School of Geography - Research Publications
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ItemHydrological controls on oviposition habitat are associated with egg-laying phenology of some caddisflies(WILEY, 2021-07)Abstract Seasonal variation in resource availability can have strong effects on life histories and population densities. Emergent rocks (ERs) are an essential oviposition resource for multiple species of stream insects. The availability of ERs depends upon water depth and clast size, which vary with discharge and river geomorphology, respectively. Recruitment success for populations may depend on whether peak egg‐laying periods occur at times when ERs are also abundant. For multiple species that oviposit on ERs, we tested whether seasonal fluctuations in ER abundance were concurrent with oviposition phenology. We also tested whether high discharge drowned ERs for sufficiently long periods to preclude egg laying, and whether this problem varied between rivers differing in channel morphology and particle size distribution. We obtained a continuous timeseries of water level (WL) measured every 30 min for 2 years at sites on three rivers in south‐eastern Australia with similar hydrology but different geomorphology. A relationship between WL and ER numbers was determined empirically at each site and these relationships were used to predict ER availability over the 2 years. Egg masses of 10 species of caddisflies were enumerated each month for a year in one river to establish oviposition phenology. Abundance of ERs was inversely related to discharge in all three rivers. ERs were most abundant during autumn and scarce during spring. Site‐specific geomorphology resulted in skewed or multimodal distributions of ER abundance each year. Between years, catchment‐scale hydrometeorology mediated patterns of ER availability, despite the close proximity of sites. Temporal variance in ER availability was not consistently correlated with mean WL or WL variance. ER variance increased with WL variance, when WL was below a threshold equivalent to mean annual WL. Above this threshold, most ERs were likely to be submerged. Oviposition phenology varied strongly among the 10 species of caddisflies, with egg‐laying ranging from 1–2 months to year‐round. Temporal variations in ER and egg mass abundance were not correlated for most species. Below a threshold minimum number of ERs, egg masses were highly crowded onto the few available ERs, which is evidence that ERs were in short supply. For five species, high egg mass abundance was positively associated with periods of the year when the time above the threshold number of ERs was high. Unusually, two species laid most egg masses during winter and when the time above this threshold was short. Three species showed no association between egg mass abundance and time above this threshold; two of these species laid eggs year‐round. Regional hydrometeorology controlled the availability of ERs, but between‐river differences were sufficient to deliver different outcomes in the availability of oviposition sites between years and seasons. Caddisflies were rarely prevented from laying eggs but periods when ERs were in short supply created crowding, which may be associated with negative fitness effects on hatching larvae. Geomorphological controls on availability of oviposition resources may have strong implications for the coexistence of species that overlap in egg‐laying phenology.
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ItemCapturing geomorphologial patterns in ecological resources: fractal dimensions describe fluvial rock distributions( 2020-12-02)Oral presentation at the annual meeting of the Ecological Society of Australia in December 2020
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ItemExplaining species diversity in a fractal world( 2020-12-01)Oral presentation at the annual meeting of the Ecological Society of Australia, Dec 2020
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ItemA novel method reveals how channel retentiveness and stocks of detritus (CPOM) vary among streams differing in bed roughness(Wiley, 2020-08)1. Coarse particulate organic matter (CPOM) is a fundamental resource in freshwater streams, providing food, shelter and habitat for diverse invertebrate taxa and playing a key role in metabolism in low‐order streams. Benthic CPOM stocks are determined by rates of supply and breakdown of detritus and by channel retentiveness (i.e. the capacity for the channel to trap and retain CPOM). We focussed on factors affecting the retentiveness of channels, which theoretically differs among streams with different sediment sizes and concomitant channel morphology. 2. We developed a new, rapid method to measure retentiveness using line‐intercept surveys along transects. With this rapid approach, we surveyed 32 sites from three types of streams (smooth sandy channels, n = 10; gravel channels of intermediate roughness, n = 12; rough cobble channels, n = 10) in Victoria, south‐eastern Australia, and tested the simple hypotheses that: (1) retentiveness increases in channels with increasing channel roughness (i.e. sandy versus gravel versus cobble‐bed streams); (2) different types of channel features (e.g. log jams, cobbles, depositional areas) differ in the efficiency with which they retain CPOM. The line‐intercept survey method was readily adapted to measure retentiveness as m of retentive structure per m of transect (i.e. the Linear Coverage Index) and trapping efficiency as m of CPOM per m of retentive element, for 10 different types of retentive elements. 3. Unexpectedly, the retentiveness of channels did not increase with channel roughness. This occurred because channels with different roughness were dominated by different types of retentive structure. Retentive structure in cobble sites was dominated by cobbles themselves, which were highly retentive in other studies but poorly retentive in our system. Gravel and sand sites had more log jams and depositional areas, such as pools and backwaters, and these features were more effective at trapping CPOM. Thus, retention of CPOM was highest in gravel and sand sites. 4. Our method provides a new tool for investigators testing hypotheses about CPOM retention in streams. The method is rapid, requires a minimum of equipment and personnel, and may be applied in any wadeable stream. Retentiveness is calculated in intuitive units that are directly comparable among sites and may have utility as variables in models of CPOM dynamics. We hope this method will open up new avenues for research that may shed light on how CPOM stocks vary among streams, with implications for diversity of aquatic fauna and ecosystem functions such as decomposition.
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ItemTerrestrial-aquatic transitions: Local abundances and movements of mature female caddisflies are related to oviposition habits but not flight capability(Wiley, 2020-01-09)1. Movement behaviours of adult aquatic insects can produce distinct spatial distribution patterns. Studies of adult abundance with distance away from water bodies are common and may invoke flight capability to explain species differences. In contrast, distribution patterns along river channels are poorly described, but are no less important for understanding population dynamics. Longitudinal patterns in adult abundance along short river lengths may differ between sexes and at different life stage transitions between aquatic and terrestrial environments, i.e. at emergence and oviposition. Flight capability is unlikely to influence longitudinal patterns created at emergence, but may influence local abundances of mature females seeking to lay eggs. We tested hypotheses about how local abundances of mature females might differ according to oviposition habits and flight capability. 2. We surveyed abundances of mature female caddisflies at adjacent riffle–pool pairs along short river lengths with homogeneous riparian cover. Our survey included nine species in three families (Hydrobiosidae, Leptoceridae, Hydropsychidae), which encompassed multiple different oviposition habits and a range of wing sizes and shapes. Several of the species oviposit preferentially in riffles. Accordingly, we tested for differences in female abundance between channel units (adjacent riffle–pool pairs). We also tested whether females attained higher abundances in some places along channels than others (i.e. over larger spatial scales and regardless of channel unit) which imply movements along the channel and aggregation in some locations. Wing morphology was used as a proxy measure of flight capability and included measures of wing span, area, aspect ratio and the second moment of wing area. 3. Three distinctly different distribution patterns of mature female caddisflies were identified. The abundance of three species varied over larger scales only (multiple channel units). Six species that oviposit preferentially in riffles had higher female abundances at riffles than pools, but for only one did abundances also vary over larger scales. There was no association between these different patterns and measures of wing morphology, after removing metrics that were correlated and that differed systematically between taxonomic families. However, we could not reject the hypothesis that some aspect of flight behaviour may have contributed to observed patterns. 4. The diverse but distinct distributions of mature female caddisflies we observed along short channel lengths are novel and suggest that species differ in their propensity for movement along streams, which could have consequences for local densities of eggs and juveniles in the aquatic environment. The degree to which population sizes are coupled across the terrestrial‐to‐aquatic transition is rarely investigated in aquatic insects and may provide fresh insight into sources of spatial variation within
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ItemAvoidance and aggregation create consistent egg distribution patterns of congeneric caddisflies across spatially variable oviposition landscapes.(Springer Nature, 2020-02)Amongst oviparous animals, the spatial distribution of individuals is often set initially by where females lay eggs, with potential implications for populations and species coexistence. Do the spatial arrangements of oviposition sites or female behaviours determine spatial patterns of eggs? The consequences of spatial patterns may be context independent if strong behaviours drive patterns; context dependent if the local environment dominates. We tested these ideas using a guild of stream-dwelling caddisflies that oviposit on emergent rocks, focussing on genera with contrasting behaviours. In naturally occurring oviposition landscapes (riffles with emergent rocks), we surveyed the spatial arrangement and environmental characteristics of all emergent rocks, identified and enumerated egg masses on each. Multiple riffles were surveyed to test for spatially invariant patterns and behaviours. In landscapes, we tested for spatial clumping of oviposition sites exploited by each species and for segregation of congeneric species. At oviposition sites, we characterised the frequency distributions of egg masses and tested for species associations. Genus-specific behaviours produced different spatial patterns of egg masses in the same landscapes. Congregative behaviour of Ulmerochorema spp. at landscape scales and an aggregative response at preferred oviposition sites led to clumped patterns, local aggregation and species overlap. In contrast, avoidance behaviours by congeners of Apsilochorema resulted in no or weak clumping, and species segregation in some landscapes. Spatial patterns were consistent across riffles that varied in area and oviposition site density. These results suggest that quite different oviposition behaviours may be context independent, and the consequences of spatial patterns may be spatially invariant also.