Invasion of the shelter snatchers: behavioural plasticity in invasive red swamp crayfish,Procambarus clarkii

1. In many freshwater systems, competition for shelter plays an important role in determining the persistence of both native and alien species. The red swamp crayfish, Procambarus clarkii, is currently invading the native habitat of the signal crayfish, Pacifastacus leniusculus, in southern Oregon, and interspecific competition for shelter may be driving the species replacement in this region. 2. We designed a 2 × 3 factorial mesocosm experiment, with shelter density and species combination as factors, to investigate shelter occupancy and resource competition. Contrary to our predictions, the two crayfish species are equal competitors for shelter. Further, the invasive P. clarkii modified its shelter occupancy behaviour in the presence of the native P. leniusculus and has broader microhabitat preferences. 3. Specifically, we found that P. clarkii alters shelter occupancy and space use patterns when the two species occurred together, such that shelter use was identical between P. clarkii and P. leniusculus in mixed‐species treatments. In such treatments, both species increased their use of shelters when shelter density increased. When P. clarkii was alone, however, individuals did not alter shelter use as a function of shelter density, whereas P. leniusculus exhibited similar density‐dependent behaviour in both mixed‐ and single‐species treatments. 4. In a complementary field survey, we employed an ‘epicentre‐based’ design to sample two field sites. We observed patterns of microhabitat use and breadth for each species similar to those in our mesocosm experiment: the invasive P. clarkii was more abundant across different habitats and used a broader range of microhabitats than the native P. leniusculus. As such, we found that P. clarkii was more abundant across both field sites than the P. leniusculus, occupying microhabitats within and beyond the preferred range of P. leniusculus. Both field sites were affected by urban development and agriculture. 5. The use of microhabitats by both species was similar in the laboratory and the field. This study confirms that P. clarkii individuals can, and do, successfully occupy microhabitats preferred by P. leniusculus in the Willamette Valley. The results from our study may be relevant to other freshwater systems inhabited by P. clarkii and contribute to the understanding of ‘niche opportunity’, a concept which defines the environmental conditions that promote biological invasions.     

Energetic Responses of Salmon to Temperature. A Study of Some Thermal Relations in the Physiology and Freshwater Ecology of Sockeye Salmon (Oncorhynchus nerkd)

SYNOPSIS. Studies on the relation of temperature to tolerance,preference, metabolic rate, performance, circulation, and growthof sockeye salmon all point to a physiological optimum in theregion of 15°C. Natural occurrence is limited in time andspace at temperatures above 18°C despite being able to tolerate24°C. Forms of physiological inadequacy can be demonstratedwhich account for such restrictions in distribution. Predictivepower for locating and accounting for concentrations of youngfish in thermally stratified lakes appeared to provide "proof"for the controlling influence of the physiological optimum temperature.Early literature on the ecology of sockeye supported this view.Recent studies using midwater trawls and sonar detection reveala diurnal behavior pattern which points to a more subtle interactionof biotic andabiotic factors governing vertical distributionin which the controlling force appears to be bioenergetic efficiency.It is concluded that a mechanism of behavioral thermoregulationhas evolved which favorably balances daily metabolic expendituresin order to conserve energy when food is limited.     

Host-specific pit-forming epizoans on Silurian crinoids

Brett, Carlton E. 197807 15: Host-specific pit-forming epizoans on Silurian crinoids. Lethaia , Vol. 11. pp. 217–232. Oslo. ISSN 0024–1164.
Circular-parabolic pits occur commonly on the endoskeletal remains of certain Paleozoic crinoids. Detailed study of several hundred specimens, representing about 30 pelmatozoan species from the Upper Silurian Rochester Shale of New York and Ontario, reveals that such pits occur exclusively in seven species of crinoids. Furthermore, there are consistent differences in the morphology and orientation of holes occurring on the different crinoid species. This suggests that distinct epizoan species settled selectively on given hosts. The relationship between the hole-producing epizoans and crinoid hosts is inferred to have been a form of dependent commensalism. Preliminary surveys of other Paleozoic crinoid assemblages reveal similar host-selectivity by pit-producing epizoans. Crinoidepizoan pairs apparently co-evolved through considerable spans of geologic time as related genera and species of different ages, from Silurian to Pennsylvanian, exhibit similar pits.     

Parallel host range expansion in two unrelated cossid moths infesting Eucalyptus nitens on two continents

1. Two cossid moths, Coryphodema tristis Drury and Chilecomadia valdiviana Philippi, have recently become pests on Eucalyptus nitens H. Deane & Maiden in South Africa and Chile, respectively. Both C. tristis and C. valdiviana have large host ranges and high levels of similarity in their host distributions. Their infestations of E. nitens are the first records of these moths on Myrtaceae. 2. The contemporaneous adoption of E. nitens as a novel host, despite widespread availability of native and introduced Myrtaceae, suggests a non‐random pattern of invasion. Phylogenetic relatedness among the two species linked to cryptic invasion of one or both moths at some time in the recent past provides a possible explanation for this pattern. 3. To test this hypothesis, variation in mtDNA sequences for the COI gene of C. tristis and C. valdiviana were analyzed. The COI mtDNA sequence data showed that C. tristis and C. valdiviana are highly divergent genetically, indicating that both are native on their respective continents with independent evolutionary trajectories. 4. The parallel host range expansions to E. nitens on different continents appear to be unrelated events, likely driven by characteristics of the biology and/or ecology of the host.