A global overview of dam-based impacts on large river systems shows that over half (172 out of 292) are affected by dams, including the eight most biogeographically diverse. Dam-impacted catchments experience higher irrigation pressure and about 25 times more economic activity per unit of water than do unaffected catchments. In view of projected changes in climate and water resource use, these findings can be used to identify ecological risks associated with further impacts on large river systems.

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Fragmentation and flow regulation of the world's large river systems

Much as Rachel Carson's \"Silent Spring\" was a call to action against the pesticides that were devastating bird populations, Charles S. Elton's classic \"The Ecology of Invasions by Animals and Plants\" sounded an early warning about an environmental catastrophe that has become all too familiar today-the invasion of nonnative species. From kudzu to zebra mussels to Asian long-horned beetles, nonnative species are colonizing new habitats around the world at an alarming rate thanks to accidental and intentional human intervention. One of the leading causes of extinctions of native animals and plants, invasive species also wreak severe economic havoc, causing $79 billion worth of damage in the United States alone. Elton explains the devastating effects that invasive species can have on local ecosystems in clear, concise language and with numerous examples. The first book on invasion biology, and still the most cited, Elton's masterpiece provides an accessible, engaging introduction to one of the most important environmental crises of our time. Charles S. Elton was one of the founders of ecology, who also established and led Oxford University's Bureau of Animal Population. His work has influenced generations of ecologists and zoologists, and his publications remain central to the literature in modern biology. \"History has caught up with Charles Elton's foresight, and \"The Ecology of Invasions\" can now be seen as one of the central scientific books of our century.\"-David Quammen, from the Foreword to \"Killer Algae: The True Tale of a Biological Invasion\

The Ecology of Invasions by Animals and Plants

Animal migrations span the globe, involving immense numbers of individuals from a wide range of taxa. Migrants transport nutrients, energy, and other organisms as they forage and are preyed upon throughout their journeys. These highly predictable, pulsed movements across large spatial scales render migration a potentially powerful yet underappreciated dimension of biodiversity that is intimately embedded within resident communities. We review examples from across the animal kingdom to distill fundamental processes by which migratory animals influence communities and ecosystems, demonstrating that they can uniquely alter energy flow, food-web topology and stability, trophic cascades, and the structure of metacommunities. Given the potential for migration to alter ecological networks worldwide, we suggest an integrative framework through which community dynamics and ecosystem functioning may explicitly consider animal migrations.

https://science.sciencemag.org/content/sci/344/6179/1242552.full.pdf

Migratory Animals Couple Biodiversity and Ecosystem Functioning Worldwide

Since their first use in the mid-1980s, passive integrated transponder devices (PIT tags) have allowed innovative investigations into numerous biological traits of animals. The tiny, coded markers injected into individual animals allow assessment of growth rates, movement patterns, and survivorship for many species in a manner more reliable than traditional approaches of externally marking animals for identification. PIT tags have also been used to confirm the identity of zoo animals, pets, and protected species that have been illegally removed from the wild. New approaches with PIT tags herald advances in physiology and conservation biology, as well as greater understanding of social interactions among individuals in a population. Despite their current limitations, including high purchase cost, low detection distance, and potential tag loss in some circumstances, PIT tags offer many opportunities to unravel animal mysteries that heretofore could not be addressed effectively.

https://bioone.org/journals/BioScience/volume-54/issue-5/0006-3568(2004)054[0447:PTSTAI]2.0.CO;2/PIT-Tagging-Simple-Technology-at-Its-Best/10.1641/0006-3568(2004)054[0447:PTSTAI]2.0.CO;2.pdf

PIT Tagging: Simple Technology at Its Best

Ecological invasions, where non-native species spread to new areas, grow to high densities and have large, negative impacts on ecological communities, are a major worldwide problem. Recent studies suggest that one of the key mechanisms influencing invasion dynamics is personality-dependent dispersal: the tendency for dispersers to have a different personality type than the average from a source population. We examined this possibility in the invasive mosquitofish (Gambusia affinis). We measured individual tendencies to disperse in experimental streams and several personality traits: sociability, boldness, activity and exploration tendency before and three weeks after dispersal. We found that mosquitofish display consistent behavioural tendencies over time, and significant positive correlations between all personality traits. Most notably, sociability was an important indicator of dispersal distance, with more asocial individuals dispersing further, suggesting personality-biased dispersal on an invasion front. These results could have important ecological implications, as invasion by a biased subset of individuals is likely to have different ecological impacts than invasion by a random group of colonists.

Personality traits and dispersal tendency in the invasive mosquitofish (Gambusia affinis)

Migration And Spatial Behaviour: Introduction. The Stimulus And Capacity For Migration: Stimuli For Migration, The Capacity For Migration, Piloting, Orientation And Navigation. Types Of Migration: Migrations At The Seasonal And Ontogenetic Scale, Diel Horizontal And Vertical Migrations. Patterns Of Migratory Behaviour In Freshwater Fishes: Arctic And Subarctic Regions, Temperate Regions, Tropical Regions. Taxonomic Analysis Of Migration In Freshwater Fishes, Lampreys Through To Freshwater--Dwelling Flatfishes (In 45 Sections). Methods For Studying The Spatial Behaviour Of Fishes In Fresh--And Brackish Water: Capture Dependent Methods, Capture Independent Methods, Choice Of Methods In Fish Migration Studies. Applied Aspects Of Freshwater Fish Migration: The Impact Of Mana s Activities On Freshwater Fish Migration. Mitigation Of Hazards And Obstacles To Fish Migration, Installation, Monitoring And Efficiency Of Fish Passes. Conclusions. Indexes

Migration of Freshwater Fishes

1. The American signal crayfish Pacifastacus leniusculus, an invasive species widely introduced throughout Europe, is a major threat to native European crayfish species and is causing increasing concern because of its wide impact on aquatic ecosystems.

2. Whilst various control and management methods have been proposed, very little is known about the factors influencing dispersal and movements of signal crayfish.

3. Sixty-four adult signal crayfish (carapace length 31.9–63.8 mm) were radiotagged in upland rivers in northern England, during four periods. Tracking was carried out at two sites, a low-density establishing population and a high-density established population. Tracking was carried out at both sites concurrently during midsummer (June to August 2002), during late summer (August to September 2001) at the low-density population site and during autumn to winter (October to February 2000/01) at the high-density population site.

4. Maximum movement occurred during midsummer. Temperature appeared to be a major factor influencing the timing and extent of movements between tracking periods.

5. The frequency distribution of the maximum distance moved upstream and downstream by radiotagged crayfish showed an inverse power relationship. The median maximal upstream and downstream distances moved were 13.5 m (range 0–283 m) and 15 m (range 0–417 m), respectively. There was a significant difference between the distributions of upstream and downstream ranges, with greater distances moved downstream.

6. All downstream movements made by crayfish appeared to be active movements and not the result of passive movement during periods of high discharge. There was no apparent influence of size, sex or density on the amount of movement recorded.

7. The study provides important information on the spatial and temporal behaviour of introduced crayfish in upland lotic systems. In contrast to lowland rivers, our results suggest that flow or gradient may influence the invasive potential of signal crayfish in an upstream direction in upland rivers.

Movement and dispersal of the invasive signal crayfish Pacifastacus leniusculus in upland rivers

SUMMARY 1. Radio-telemetry and mark-recapture methods were used to study the summer movements of adult and juvenile white-clawed crayfish, Austropotamobius pallipes from a wild population in a small braided stream, Dalton Beck, North Yorkshire, U.K. Radiotransmitters were attached to the chelae of 18 large (> 35 mm carapace length) crayfish and individuals were subsequently located to within 0.15 m. Additionally a total of 888 crayfish were marked with carapace brands, and 83 were recaptured. 2. Radio-tracked crayfish exhibited significantly greater local activity at dusk (21.00‐00.00) than at dawn (03.00‐06.00), or during morning (09.00‐12.00) and afternoon (15.00‐18.00) monitoring periods. 3. The greatest movements of radio-tracked crayfish occurred within 2 days of release. After this time, periods of residence were interspersed by movements to new locations, interpreted as establishment of ephemeral home areas. It is suggested that the initial large movements were the result of a ‘fright response‘ following capture. 4. Movements varied widely between individuals, some moving more than 300 m in 10 days, while others showed little movement over an equivalent time period. Mean (aSE) daily movements were 4.6 a 3.0 m for males and 1.5 a 1.0 m for females. Although crayfish often used specific home sites for in excess of 7 days, displaced animals did not return to home sites. 5. The total distances travelled and the mean distance travelled per day by individual radio-tagged crayfish did not differ significantly between upstream or downstream directions or between males and females. This was also the case for marked crayfish used in mark-recapture studies. 6. Positive correlations between distance moved per day and size (carapace length) were found for downstream movements by male and female crayfish, but not for upstream movements. 7. Some preliminary observations of the response of crayfish to flood events suggested that these could be catastrophic with two out of five tracked crayfish found dead after a high stream-discharge event.

Ranging behaviour of a large freshwater invertebrate, the white‐clawed crayfish Austropotamobius pallipes

1. Dispersal and habitat use are key elements in determining impacts of introduced species. We examined if an invasive crayfish species showed a different pattern of movement, dispersal and refuge use to that of a species that it displaces.

2. Fifteen adults of the introduced American signal crayfish, Pacifastacus leniusculus and 20 adult native white-clawed crayfish Austropotamobius pallipes were radiotagged in an area of river where in 2003 they co-occurred and the spatial behaviour and habitat use of the two species were examined. Subsequent surveys at the study site in 2005 recorded no A. pallipes and the density of P. leniusculus had increased.

3. Clear differences in the spatial behaviour of the two species were found. The median distance moved per day by signal crayfish was over twice that of white-clawed crayfish, and dispersal from release locations was higher in signal crayfish. A similar range of refuges with a high degree of overlap was used by both species suggesting that the potential for competitive interaction between the two species exists.

4. The greater movement and dispersal by signal crayfish recorded here supports the hypothesis that invaders are better dispersers than the species that they displace. In addition, movements by signal crayfish may allow them to make better use of patchy resources than white-clawed crayfish and this, coupled with similar microhabitat use, may contribute to the observed replacement.

Movement, dispersal and refuge use of co-occurring introduced and native crayfish

A method for tracking crayfish and other benthic animals in rivers and streams, based on passive integrated transponder (PIT) technology, using a portable detector was investigated. The effect of implanting crayfish with PIT tags and the efficiency of the PIT tag detector system at locating tags is described. In a laboratory study 30 signal crayfish Pacifastacus leniusculus (>33.7 mm carapace length) were internally implanted with PIT tags (12-mm long×2.1-mm diameter) and 30 crayfish matched for size and sex were kept as controls and maintained for 6 months. Tagging had no significant effect on survival, moulting or growth of crayfish, and tag retention was 100%. The reader unit consists of an antenna coil mounted on a pole and designed to be moved over the streambed to search for tagged crayfish. Efficiency testing indicated that more than 80% of tags were identified and located when hidden within different stream microhabitats.

Timothy J. Thom

Papers

Migration of Freshwater Fishes

Movement and dispersal of the invasive signal crayfish Pacifastacus leniusculus in upland rivers

Ranging behaviour of a large freshwater invertebrate, the white‐clawed crayfish Austropotamobius pallipes

Movement, dispersal and refuge use of co-occurring introduced and native crayfish

The potential use of PIT telemetry for identifying and tracking crayfish in their natural environment