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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ItemCoexistence of predatory caddisfly species may be facilitated by variations in the morphology of feeding apparatus and diet(WILEY, 2020-12-24)1. The hypothesis of community‐wide character displacement (CWCD) predicts that coexisting species in the same guild should differ in morphological traits associated with resource acquisition, such that interspecific competition is unlikely. Hypothesis tests often focus on trophic structures involved in food acquisition, because variations in the morphology of foraging apparatus and diet composition may be directly related. Empirical evidence of such associations among sympatric guild members is, however, uncommon. 2. The predatory larvae of caddisflies in the family Hydrobiosidae are ideal for studies of CWCD because the morphology of the prehensile foreleg, used to capture prey, varies markedly among genera. Further, hydrobiosids typically occur as species‐rich guilds, often with 10–20 species in a single community. Although the larvae are known to be predatory, detailed information on the diet of coexisting species is scarce. This study tested whether larval diet varied among multiple, sympatric species of hydrobiosid caddisflies that differed in foreleg morphology. 3. Larval specimens were collected in summer and primarily from one river in central Victoria, Australia. Gut contents of late instar larvae were examined to describe diet composition, and diet was compared among taxa using measures of diet breadth and overlap. 4. Seven sympatric species from six genera that differed in foreleg morphology were collected and late instar larvae were exclusively carnivorous. Diet composition and breadth varied markedly among some species, and diet was associated with morphology of the prehensile foreleg. Specialist predator species consumed predominantly chironomids and had high diet overlap. Generalists consumed primarily chironomids and mayflies, but overlap varied depending upon the preferred mayfly family and representation of other prey items, such as blackflies and insect eggs. All predator species consumed some caseless caddisflies and intraguild predation was strong in at least one species. 5. The marked differences in diet and foreleg morphology among hydrobiosid species are consistent with the notion that CWCD influences guild membership and may facilitate species coexistence within guilds that are typically species‐rich. Although rarely considered for freshwater communities, CWCD may help explain species membership within other guilds. The magnitude of diet variations among genera within this family are more usually found across multiple families or orders, demonstrating that assumptions about the diet of even closely related taxa may be erroneous.
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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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ItemUsing fractal dimension to capture ecologically-relevant physical variation in streams( 2017)Abstract of the oral presentation at the Annual General Meeting of the Australian Society for Limnology in 2017.
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ItemExplaining species diversity in a fractal world( 2019)Conference presentation at the Ecological Society of America annual meeting, 2019 Also given at the Australian Freshwater Sciences Society annual meeting in 2019
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ItemEgg masses of some stream-dwelling caddisflies (Trichoptera: Hydrobiosidae) from Victoria, Australia(Wiley, 2019-08-01)Eggs are a largely neglected life stage in most ecological studies of aquatic insects, despite the importance of oviposition behaviour and fecundity estimates for many research questions. Incorporating egg stages into ecological research requires that ecologists can identify and quantify eggs, but descriptions of eggs and egg masses are scarce for many groups and particularly for Australian taxa. This paper focusses on stream-dwelling caddisflies in the family Hydrobiosidae and provides species-level identifications, morphological descriptions and images of egg masses of some species that commonly occur in south-eastern Australia. All the species we identified laid plaque-shaped egg masses attached to the underside of river rocks that protrude above the water surface. These egg masses can be identified in the field with the naked eye or the aid of a low-magnification hand lens. Interspecific variations in egg mass morphology were primarily thickness and firmness of the spumaline layer, egg mass size and arrangement of eggs within the mass. We also provide some ecological information on clutch sizes and the physical characteristics of oviposition sites, and we discuss various ways in which these taxa could be exploited as model systems for ecological research.
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ItemCelebrating women conducting research in freshwater ecology ... and how the citation game is damaging them(CSIRO Publishing, 2019-01-01)We highlight women's contributions to freshwater ecology by firstly considering the historical context and gender-based barriers faced by women attempting to gain an education and secure research jobs in science over the past 100+ years. The stories of four remarkable, pioneering women in freshwater ecology (Kathleen Carpenter, Ann Chapman, Rosemary Lowe-McConnell and Ruth Patrick) illustrate the impact of barriers, emphasise the significance of their contributions and provide inspiration for the challenges ahead. Women still face barriers to participation in science, and the second part of the paper focuses on a current form of discrimination, which is citation metrics used to measure the 'quality' or 'impact' of research. We show that arguments that citation metrics reflect research quality are logically flawed, and that women are directly disadvantaged by this practice. Women are also indirectly disadvantaged in ecology because they are more likely to carry out empirical than theoretical research, and publications are generated more slowly from empirical research. Surveys of citation patterns in ecology reveal also that women are less likely to be authors of review papers, which receive three times more citations than do original articles. Unless unfettered use of citation metrics is stopped, research will be damaged, and women will be prominent casualties.
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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.