Bigger is not necessarily better: empirical tests show that dispersal proxies misrepresent actual dispersal ability.

Tests for the role of species' relative dispersal abilities in ecological and biogeographical models rely heavily on dispersal proxies, which are seldom substantiated by empirical measures of actual dispersal. This is exemplified by tests of dispersal-range size relationships and by metacommunity research that often features invertebrates, particularly freshwater insects. Using rare and unique empirical data on dispersal abilities of caddisflies, we tested whether actual dispersal abilities were associated with commonly used dispersal proxies (metrics of wing size and shape; expert opinion).

A large-scale field experiment across six rivers illustrates how the effects of resource enrichment are context dependent.

Resource supplementation can increase species richness and change the faunal composition of communities, but experiments have produced variable outcomes. An often overlooked element is that species richness can only increase if new taxa can disperse to resource-rich locations and invade established, local communities. We experimentally increased a basal resource (detritus) in six rivers in south-eastern Australia by driving wooden stakes into the riverbed to increase retention of detritus.

Multiyear resource enrichment creates persistently higher species diversity in a landscape-scale field experiment.

Short-term resource enrichment can increase species diversity in communities, but prolonged resource enrichment may result in either a diversity collapse or persistent high species diversity if fluctuation-dependent mechanisms of species coexistence are triggered. We tested the effects of resource enrichment on stream invertebrates by boosting densities of benthic detritus. In a 22-km stream length, we used wooden stakes to enhance retention of detritus at 40-m-long sites; other sites acted as controls.

Just add water: rapid assembly of new communities in previously dry riverbeds, and limited long-distance effects on existing communities.

Barriers preventing species from dispersing to a location can have a major influence on how communities assemble. Dispersal success may also depend on whether dispersers have to colonise an established community or a largely depauperate location. In freshwater systems, dams and weirs have fragmented rivers, potentially limiting dispersal of biota along rivers.

Avoidance and aggregation create consistent egg distribution patterns of congeneric caddisflies across spatially variable oviposition landscapes.

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.

Aquatic versus Terrestrial Insects: Real or Presumed Differences in Population Dynamics?

The study of insect populations is dominated by research on terrestrial insects. Are aquatic insect populations different or are they just presumed to be different? We explore the evidence across several topics. (1) Populations of terrestrial herbivorous insects are constrained most often by enemies, whereas aquatic herbivorous insects are constrained more by food supplies, a real difference related to the different plants that dominate in each ecosystem.

Dispersal traits may reflect dispersal distances, but dispersers may not connect populations demographically.

Ecological traits that reflect movement potential are often used as proxies for measured dispersal distances. Whether such traits reflect actual dispersal is often untested. Such tests are important because maximum dispersal distances may not be achieved and many dispersal events may be unsuccessful (without reproduction).

A landscape-scale field experiment reveals the importance of dispersal in a resource-limited metacommunity.

Dispersal may play a strong role in driving species diversity across landscapes. Theoretically, dispersal permits species to remain extant within a metacommunity, even if they are periodically excluded from some local communities. Field tests of dispersal effects are difficult, and most non-experimental data suggest that environmental conditions play the predominant role in setting species diversity.

Population densities and density-area relationships in a community with advective dispersal and variable mosaics of resource patches.

Many communities comprise species that select resources that are patchily distributed in an environment that is otherwise unsuitable or suboptimal. Effects of this patchiness can depend on the characteristics of patch arrays and animal movements, and produce non-intuitive outcomes in which population densities are unrelated to resource abundance. Resource mosaics are predicted to have only weak effects, however, where patches are ephemeral or organisms are transported advectively.

Lasting effects of maternal behaviour on the distribution of a dispersive stream insect.

1. Predicting population dynamics at large spatial scales requires integrating information about spatial distribution patterns, inter-patch movement rates and within-patch processes. Advective dispersal of aquatic species by water movement is considered paramount to understanding their population dynamics.

Environmental constraints on oviposition limit egg supply of a stream insect at multiple scales.

Species with complex life cycles pose challenges for understanding what processes regulate population densities, especially if some life stages disperse. Most studies of such animals that are thought to be recruitment limited focus on the idea that juvenile mortality limits the density of recruits (and hence population density), fewer consider the possibility that egg supply may be important. For species that oviposit on specific substrata, environmental constraints on oviposition sites may limit egg supply.

Does dispersal control population densities in advection-dominated systems? A fresh look at critical assumptions and a direct test.

1. In advection-dominated systems (both freshwater and marine), population dynamics are usually presumed to be dominated by the effects of migrants dispersing by advection, especially over the small spatial scales at which populations can be studied, but few studies have tested this presumption. We tested the hypothesis that benthic densities are controlled by densities of dispersers for two aquatic insects in upland streams.

Separating natural responses from experimental artefacts: habitat selection by a diadromous fish species using odours from conspecifics and natural stream water.

Animals use sensory stimuli to assess and select habitats, mates and food as well as to communicate with other individuals. One way they do this is to use olfaction, whereby they identify and respond to chemical cues. All organisms release odours, which mix with other chemical substances and ambient environmental conditions.

Experimental evidence for physical cues involved in oviposition site selection of lotic hydrobiosid caddis flies.

Cues involved in determining the distribution of invertebrate propagules within a stream landscape contribute greatly to our knowledge of the supply and arrangement of new recruits and thus an improved understanding of factors that might ultimately affect population parameters. Previous observations indicated that both current velocity and rock size were important determinants of the egg mass distribution of certain hydrobiosid caddis flies that lay their eggs in single masses beneath emergent rocks. These observations were tested experimentally in a temperate, upland Australian stream.

Spatial and temporal variation in recruitment and its effects on regulation of parasite populations.

Variation in recruitment rates of parasites to hosts possibly contributes significantly to fluctuations in parasite numbers, yet is almost never measured directly in the field. I measured the variation in recruitment rates of three species of parasitic mites living in two species of freshwater mussels over several spatial and temporal scales. I also examined separately the effect of spatial dispersion of hosts on mite recruitment.

Competition between mobile species using patchy resources: an example from a freshwater, symbiotic assemblage.

Three species of freshwater mites that are symbiotic with mussels in St Mark's River, north Florida, have consistently high rates of colonization to and occupy high proportions of mussels. The mites Unionicola poundsi and U. serrata are territorial and have limited numbers/host, whereas the non-territorial U.

Guild structure in water mites (Unionicola spp.) inhabiting freshwater mussels: choice, competitive exclusion and sex.

Unionicolid water mites inhabit freshwater unionid mussels during the nymphal and adult stages of their life-cycle. Regular sampling of mussels from two sites in St. Mark's River, Fl.

Recruitment of marine invertebrates: the role of active larval choices and early mortality.

Spatial variation in the recruitment of sessile marine invertebrates with planktonic larvae may be derived from a number of sources: events within the plankton, choices made by larvae at the time of settlement, and mortality of juvenile organisms after settlement, but before a census by an observer. These sources usually are not distinguished.A study of the recruitment of four species of sessile invertebrates living on rock walls beneath a kelp canopy showed that both selection of microhabitats by settling larvae and predation by fish may be important.