Terrestrial and Aquatic Ecology Commons^™

Resolutions Passed By The North American Crane Working Group

Proceedings of the North American Crane Workshop

FRESHWATER INFLOWS FOR CONSERVATION OF BLUE CRABS AND WHOOPING CRANES Research has shown that whooping cranes require abundant blue crab populations on which to forage to meet their energy needs. The NACWG urges the Texas Council of Environmental Quality to grant a water right to the San Marcos River Foundation at the maximum level requested (1.15 million acre-feet) to provide freshwater inflows for conservation purposes as identified in a study conducted by the Texas Parks and Wildlife Department. These inflows would increase blue crab populations, keep the bays and marshes productive in whooping crane critical habitat at Aransas, and help …

Testing A West Nile Virus Vaccine In Sandhill Cranes (Grus Canadensis), Glenn H. Olsen, Kimberli Miller, Douglas Docherty, Louis Sileo

Proceedings of the North American Crane Workshop

Eight sandhill cranes (Grus canadensis) were vaccinated with a commercial equine West Nile virus vaccine (Fort Dodge Animal Health, Fort Dodge, Iowa, USA) at the USGS Patuxent Wildlife Research Center, Laurel, Maryland, USA. Three doses of the vaccine were given, the first dose (day 0) was followed by a second 21 days later and the third dose 7 days after the second day 28 after the first dose). All doses were 0.50 ml. In addition, 5 sandhill cranes were given injections of similar amounts of sterile water on the same schedule. Blood for complete blood counts, serum chemistries, …

Migration Routes, Staging Areas, And Wintering Grounds Of Sandhill Cranes That Breed In Siberia, Gary L. Krapu, David A. Brandt

Proceedings of the North American Crane Workshop

We determined breeding sites, migration routes, spring and fall staging areas, and wintering grounds for sandhill cranes (Grus canadensis) from the midcontinent population that nest in Siberia. Our results are from 30 PTT-marked individuals captured and marked along the Platte and North Platte Rivers in Nebraska. Findings indicate the species breeds across a vast area of northeastern Siberia extending at least 1500 km west from near the Bering Strait to the Kolymskaya Plains with most breeding confined to within 75 km of the coast. We describe when PTT-tagged cranes arrived at breeding sites in Siberia, duration of stay, …

Response Of Florida Sandhill Cranes To Nest Inspection, Stephen A. Nesbitt, Paul S. Kubilis, Stephen T. Schwikert

Proceedings of the North American Crane Workshop

We observed the response of nesting Florida sandhill cranes (Grus canadensis pratensis) to 27 instances of nest inspection. The disturbed bird flew from the area 81% and walked 19% of the time. The median distance moved was 330 meters (range 28 to 480 meters). The median length of time the nest was left unattended following inspection was 50 min (range: 10 to 166 min). The median length of time that observers stayed at the nest was 16 min (range: 5 to 48 min). Ten of the nests inspected (40%) eventually failed to produce young. Statistical analysis was focused …

Patterns Of Food Use Of Wintering Whooping Cranes On The Texas Coast, Craig M. Westwood, Felipe Chavez-Ramirez

Proceedings of the North American Crane Workshop

Whooping Crane (Grus americana) fecal samples were collected from Matagorda Island National Wildlife Refuge (MINWR) during winter and fall of 1993-94 (Winter-1; n = 59), and Aransas National Wildlife Refuge (ANWR) during winter and fall of 1993-94 (n = 102) and 1994-95 (Winter-2; n = 257) to study crane diets and compare patterns of food use in these areas. Food items varied between areas, across months, and between years in both frequency and percent volume. Blue crab (Callinectes sapidus), wolfberry fruit (Lycium carolinianum), horn snail (Cerithidea pliculasa), razor clam (Tagellus plebius), …

Fecal Corticoid Monitoring In Whooping Cranes Trained To Follow Ultralight Aircraft, Barry K. Hartup, Nancy M. Czekala, Glenn H. Olsen, Julia A. Langenberg

Proceedings of the North American Crane Workshop

The use of fecal corticoid assays to measure stress in North American cranes has been limited to laboratory validation and a single field project involving reintroduced sandhill cranes (Ludders et al., 1998, 2001; Hartup et al., 2004). In 2001, we documented trends in corticoid concentrations among a cohort of ten costume-reared whooping cranes subjected to ultralight aircraft training and migration. All samples were analyzed by a validated corticosterone 125I radioimmunoassay for determination of corticoid levels. Fecal corticoid concentrations in chicks exhibited a logarithmic decline over the first 14 days after hatching (r = 0.86, p < 0.001). Fecal corticoid concentrations then stabilized at baseline levels (median 68 ng/g, range 17–186 ng/g, n = 116) during the subsequent six weeks of costume-rearing and aircraft habituation in captivity. Fecal corticoid concentrations of eight cranes increased 8-34 fold during shipment in crates to Wisconsin for field training. Increases in fecal corticoid concentrations were positively correlated with age (r = 0.81, p = 0.01), but not body weight (r = 0.44, p = 0.28) at the time of shipping. Fecal corticoid concentrations returned to baseline levels within seven days, and were sustained throughout the remainder of the training period (median 77 ng/g, range 22– 292 ng/g, n=190). Elevations in fecal corticoid concentrations were observed one (p = 0.035) and four days (p = 0.003) following physical examination and placement of leg bands compared to three days prior to the procedures (median 176 ng/g, range 116 – 553 ng/g, n = 19). Fecal corticoid concentrations decreased to pre-procedure levels within seven days. Fecal corticoid concentrations and variation during the 50 day migration period were similar to training levels in Wisconsin, except for a one day increase observed following a violent storm and escape from the temporary holding pen the preceding night (median 243 ng/g, range 228 – 280 ng/g, n = 7). There was an overall decline in fecal corticoid concentrations from the cranes during the migration (r = 0.42, p < 0.001). Acute stressors such as capture and restraint and severe storms were associated with stress responses by the cranes that varied in accordance with lasting physical or psychological stimuli. The overall process of costume-rearing, ultralight aircraft habituation, training and artificial migration was not associated with elevations in fecal corticoid concentrations suggestive of chronic stress.

New Locations And Range Extension Of Wintering Sandhill Cranes In Central Northern Mexico, Felipe Chavez-Ramirez

Proceedings of the North American Crane Workshop

The overall distribution of wintering sandhill cranes in Mexico has been reported and summarized in several prior documents. However, most reports are associated with counts or surveys primarily conducted for wintering waterfowl. Recent (1999- 2002) reports compiled from local researchers show, that wintering sandhill cranes are distributed much more widely in northern Mexico than is currently reported in the literature. The new locations reported here are primarily in the eastern portion of the Mexican Altiplano, in the states of Coahuila and Nuevo Leon, and in the southern portions of the Chihuahuan Desert Region in Zacatecas and San Luis Potosi. Most …

Evidence Of A Decline In Fat Storage By Midcontinental Sandhill Cranes In Nebraska During Spring: A Preliminary Assessment, Gary L. Krapua, David A. Brandt, Deborah A. Buhl, Gary W. Lingle

Proceedings of the North American Crane Workshop

When an ice storm killed an estimated 2,000 sandhill cranes (Grus canadensis) in the Central Platte River Valley (CPRV) in Nebraska on 24 March 1996, we retrieved the fresh carcasses of 118 adults to test for a decline in the condition of spring-staging cranes from that date in 1978 and 1979. We first conducted a principle component analysis on 3 morphological variables (tarsus, exposed culmen, and wing chord [flattened]) and used the first principal component (PC1) as an index of body size. Then, to account for variation in body mass due to size, we regressed body mass on …

An Inventory Of Rangelands In Part Of The Broome Shire, Western Australia, W E. Cotching

Technical Bulletins

The inventory of rangelands in part of the Broome Shire in Western Australia was undertaken by DAFWA between 1989 and 1990. It describes and maps the natural resources of the region’s pastoral leasehold land. This survey report provides a baseline record of the existence and condition of the natural area’s resources, to assist with the planning and implementation of land management practices. The report identified and described the condition of soils, landforms, vegetation, habitat, ecosystems, and declared plants and animals. It also assessed the impact of pastoralism and made land management recommendations. The survey of part of the Broome Shire …

Patterns Of Habitat Use By Whooping Cranes During Migration: Summary From 1977–1999 Site Evaluation Data, Jane E. Austin, Amy L. Richert

Proceedings of the North American Crane Workshop

We used site evaluation data collected during 1977–1999 to examine patterns of habitat use by whooping cranes (Grus americana) during migration through the United States portion of the Wood Buffalo–Aransas flyway. We examined characteristics of 3 types of stopover habitats: 1) roost sites (n = 141 records), 2) feeding sites (n = 306), and 3) dual-use sites (i.e., where observer recorded cranes as using a site for both roosting and feeding (n = 248). Results in spring were influenced by the large number of records from Nebraska (> 67% of spring records) and in fall by frequent observations …

Philopatry And Dispersal In Whooping Cranes, Brian W. Johns, J. Paul Goossen, Ernie Kuyt, Lea Craig-Moore

Proceedings of the North American Crane Workshop

The natal and breeding dispersal of endangered whooping cranes (Grus americana) was investigated using information collected between 1978-2002 on the nesting grounds in and near Wood Buffalo National Park, Alberta-Northwest Territories. A minimum of 77% of the juveniles color-banded near their natal sites returned to the breeding grounds. Sex-biased natal dispersal was not observed. At least 76% of first-time breeders nested within 20 km of their natal site. Pioneering was rare and most cranes nested on the primary nesting areas adjacent to the Sass and Klewi rivers. The mechanism enhancing natal philopatry is probably related to learning the …

Techniques Employed To Capture Whooping Cranes In Central Florida, Martin J. Folk, Stephen A. Nesbitt, Stephen T. Schwikert, James A. Schmidt, Kathleen A. Sullivan, Thomas J. Miller, Stephen B. Baynes, Jeannette M. Parker

Proceedings of the North American Crane Workshop

During the course of re-introduction of a non-migratory flock of whooping cranes to Florida (1993-2002) a variety of techniques were used to capture 105 free-living birds. The most commonly used technique was hand-capture from a feed trough blind (45 birds). Whooping cranes were also captured by use of snares, several types of nets, and by hand. All techniques were relatively safe and posed little risk to the birds, a primary concern when dealing with rare birds. We found it useful to employ a diversity of techniques because some methods work better than others under differing circumstances. Capturing whooping cranes for …

Head Stabilization In Whooping Cranes, Matthew R. Kinloch, Thomas W. Cronin, Glenn H. Olsen

Proceedings of the North American Crane Workshop

The whooping crane (Grus americana) is the tallest bird in North America, yet not much is known about its visual ecology. How these birds overcome their unusual height to identify, locate, track, and capture prey items is not well understood. There have been many studies on head and eye stabilization in large wading birds (herons and egrets), but the pattern of head movement and stabilization during foraging is unclear. Patterns of head movement and stabilization during walking were examined in whooping cranes at Patuxent Wildlife Research Center, Laurel, Maryland USA. Four whooping cranes (1 male and 3 females) …

Winter 2005, Nsu Oceanographic Center

Currents

No abstract provided.

Zur Nahrungsökologie Des Uhus Bubo Bubo In Der Mongolei = Feeding Ecology Of The Eagle Owl Bubo Bubo In Mongolia, Thomas Hoffmann, Michael Stubbe, D. Heidecke, R. Piechocki, R. Samjaa, J. Erfurt, D. Sumjaa

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

This paper presents further results on the food ecology of the eagle owl in western Mongolia for the years 1984 to 1992. Additional to the already known sites we investigated two new resting places. At least 27 mammal and 17 bird species were recorded. The results confirm previous studies. Small to medium sized mammals (Cricetidae, Dipodidae, Arvicolidae) dominate the prey of the eagle owl whereas birds and invertebrates are less important.

Ecology Of Soil Microarthropods In Gobi Gurvan Saykhan Mountains, Southern Mongolia, Tsedev Bolortuya, Badamdorj Bayartogtokh

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

In the present paper, we describe the community structure, species diversity, population density, and the character of distribution of soil microarthropods of the Gobi Gurvan Saykhan mountains. In total 45 species of soil microarthropods belonging to 37 genera and 24 families were identified. Twenty-seven species of soil microarthropods belonging to 25 genera and 20 families were found in the Züün Saykhan, 31 species belonging to 27 genera and 19 families in the Dund Saykhan. Oribatid mites are the dominant group (35 species = 77.8% of total species richness), while mesostigmatid mites account for 7 species (15.6 %). Other groups are …

Reproductive Ecology Of Two Common Woody Species, Juniperus Sabina And Artemisia Santolinifolia, In Mountain Steppes Of Southern Mongolia, Katrin Ronnenberg

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

The present study describes the reproductive ecology of the prostrate shrub Juniperus sabina and the dwarf shrub Artemisia santolinifolia in dry mountain steppes of southern Mongolia. Whereas stands of the juniper are located at the drought limit of the genus’ distributional range, the genus Artemisia is typical of central Asian drylands. Both species produce large numbers of reproductive organs. For Juniperus sabina, however, only 2.5% of the morphologically intact seeds were found to be viable. Correspondingly, neither seedlings nor saplings were found in the field, and recruitment by reseeding happens at most rarely under the present climatic conditions.

Instead, …

Beaver Research In The Uvs Nuur Region, Michael Stubbe, N. Dawaa, R. Samjaa, Annegret Stubbe, A. P. Saveljev, D. Heidecke, D. Sumjaa, H. Ansorge, S. Shar, J.-F. Ducroz

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

In 1985, 1988, and 2002 Castor fiber birulai was introduced to the Tes Gol of the Uvs Nuur basin in North-western Mongolia. The beavers migrated through the Republic of Tyva and settled in the middle part of Tes Gol near the Tyvinian-Mongolian border. About 10 colonies were recorded in this region in 2002. Strict protection of Castor fiber birulai has to be ensured in Mongolia and the Republic of Tyva in future.

Vergleichende Untersuchungen Zur Besiedlung Von Ausgewählten Hochgebirgen Der Nordwest- Und Südmongolei Durch Laufkäfer (Coleoptera: Carabidae) = Comparing Investigations Of The Distribution Of Carabid Beetles (Coleoptera: Carabidae) In Different High Mountain Regions In Northwest- And South Mongolia, Peer Schnitter

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

In the years 1977-1979 and 1986 two high mountain regions of Mongolia are observed, especially in regard of the carabid fauna within different altitudes. In one of the investigation areas--the mountains of Charchiraa in Northwest-Mongolia the first transect with any plots was arranged from the Mount Suslan-Chamar to the salt lake Uvs Nuur. The second transect in the mountains of Ich-bogd in South-Mongolia starts at the Mount Baruun-bogd and reaches the salt lake Orog Nuur. The species combinations are very different, only some species could be found in both areas. The carabid coenoses and their distribution within the different altitudes …

First Results Of Wild Ass Research In The South Gobi Aymag/Mongolia In 2003 And 2004, Annegret Stubbe, Michael Stubbe, N. Batsajchan, R. Samjaa, S. Doržderem

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

The population of the Mongolian wild ass belongs to the nominate form Equus hemionus hemionus described by Pallas in 1775. This species is adapted to semidesert habitats in the Gobi region and is listed in the Red Book of Mongolia as well as on appendix I of the Washington Convention (CITES). Mapping of the northern border of the distributional range showed a remarkable decrease in size in comparison to the maps of Murzaev (1954) or Bannikov (1954). The pressure of civilization, settlements, motorization, and increasing numbers of domestic livestock in connection with the occupation of water resources and illegal hunting …

Beiträge Zur Ökologie Und Verbreitung Der Steppenwühlmaus Microtus Brandti Radde, 1861 In Der Mongolei = Ecology And Distribution Of The Steppe Vole Microtus Brandti Radde, 1861 In Mongolia, N. Dawaa, Michael Stubbe, Annegret Stubbe

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

Microtus brandti is one of the most important pest species of Mongolian rodents. Since the publication of Bannikov (1954) the area of expansion is increased, in the Archangaj-Aimag 200 km westward, in the Central Aimag 70 km to the North and in the north-eastern part of Dornogov’- Aimag about 110 km to the South. In years of gradation the plant cover was exterminated up to 100%. We can distinguish a zone of exposed harmfulness with a damage of 70-100%. In this region 16 great centers of infestation were listed. Between 1925 and 1985 six important calamities were noticed, in intervals …

Der Einsatz Der Luzerne-Blattschneiderbiene, Megachile Rotundata (Hymenoptera: Megachilidae), Zur Bestäubung Von Luzerne In Der Mongolei = Management Of The Alfalfa Leaf-Cutter Bee, Megachile Rotundata (Hymenoptera: Megachilidae), For Alfalfa Pollination In Mongolia, Karsten Seidelmann, Čojrog Batchujag, Manfred Dorn

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

The propagation of the alfalfa leaf-cutter bee, Megachile rotundata was tested from 1988 to 1991 on alfalfa seed growing fields at the Uvs-Nuur Basin in the North-West of Mongolia. We used the loose-cell technology in combination with wooden grooved boards (dimensions of the nesting holes: 8 × 110 mm). The climatic conditions at the investigation area proved to be favorable for the rearing of the bees. The average temperature was above 21 °C during 8.5 h by a mean sunshine duration of 6.4 h and sporadic rainfall. Nevertheless, the night temperatures felled below 10 °C and are responsible for a …

Die Parasitierung Der Luzerne-Blattschneiderbiene, Megachile Rotundata (Hymenoptera: Megachilidae), Durch Physocephala Pusilla (Diptera: Conopidae) In Der Mongolei = Parasitization Of The Alfalfa Leaf-Cutter Bee, Megachile Rotundata (Hymenoptera: Megachilidae), By Physocephala Pusilla (Diptera: Conopidae) In Mongolia, Karsten Seidelmann

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

Physocephala pusilla Meigen (Diptera: Conopidae) was found to be a dangerous endoparasitoid of the alfalfa leafcutter bee Megachile rotundata F. (Hymenoptera: Megachilidae) in Mongolia. The conopid fly parasitizes adults and causes their early death. In 1989 and 1990, 16% and 15% respectively of the M. rotundata females were found dead in front of the bee shelter. However, the number of bees (females and males) dying in the field is unknown. These bees cause a contamination of the alfalfa fields due to an increase of the conopid population. Therefore, Ph. pusilla becomes a serious problem for the management of M. rotundata …

Facts From A Year Of Drought: Forage Competition Between Livestock And The Mongolian Pika (Ochotona Pallasi) And Its Effects On Livestock Densities And Body Condition, Vroni Retzer

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

Burrowing small mammals in grasslands have long been regarded as pests because they compete for forage with livestock and reduce the forage availability for livestock by destroying pastures through their intensive digging activity.

In order to investigate forage competition between the Mongolian Pika (Ochotona pallasi) and livestock an exclosure experiment consisting of four different treatments was set up. The treatments were: 1) accessible only for pikas, (only pika) 2) accessible only for livestock, (only livestock) 3) accessible for both herbivore groups (pika & livestock) and 4) no grazing (no grazing). During the investigation period all requirements for forage …

Wild Bactrian Camel Conservation, Richard P. Reading, Evan S. Blumer, Henry Mix, Jadamsuren Adiya

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

The wild Bactrian camel (Camelus bactrianus ferus) is critically endangered throughout its range in China and Mongolia. Yet, wild camels remain poorly understood, with knowledge derived primarily from a few short studies and anecdotal information. We initiated a wild camel conservation project to determine the reasons for camel decline and to develop a program to address those problems.

We are employing satellite telemetry to gather data on wild camel movement patterns, home ranges, habitat use, and sources of mortality. We are also collecting feces from camels and wolves to determine important forage plants and to begin to assess …

Winter Pasture Conditions And Forage Use By Argali (Ovis Ammon) In Gobi Gurvan Saykhan National Park, Bayart Mandakh, Ganchimeg J. Wingard, Richard P. Reading

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

Conservation of Argali sheep (Ovis ammon) presents a significant challenge to biologists and conservation managers in Mongolia. Argali are endangered and available data suggest that their numbers are declining. However, the mechanisms causing this decline are poorly understood. Recent research suggests that declines in Argali sheep numbers may be due in part to competition with domestic livestock for forage.

Following privatization of herd ownership in 1991, livestock numbers increased dramatically across Mongolia. With this increase, many herders expanded grazing onto more marginal rangeland resulting in increased competition with wild ungulates and displacement of Argali from their former population …

Ecology Of Argali In Ikh Nartiin Chuluu, Dornogobi Aymag, Richard P. Reading, Sukhiin Amgalanbaatar, Ganchimeg J. Wingard, Danny Kenny, Anthony Denicola

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

Argali sheep (Ovis ammon) are listed as threatened in both Mongolia and internationally. Yet, little is known about the biology and ecology of this species. Available data suggests that Argali in Mongolia are declining due to direct poaching and competition with domestic livestock. We initiated several research projects to better understand and conserve the species. In this report we discuss Argali ecology using radio telemetry.

We captured and radio-collared 36 Argali using drive-nets, lamb captures, and dating from 2000–2004. Fifteen collared animals have died: 2 due to capture techniques, 8 from predation, 1 from starvation and exposure, 1 …

Zur Populationsökologie Und Raumnutzung Der Steppenwühlmaus Microtus Brandti (Radde, 1861) In Der Fortpflanzungsperiode, Ulrich Zöphel, N. Dawaa

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

During the growing season between 1988 and 1990 the population biology of Brandt’s vole (Microtus brandti) was observed in a population near Ulaanbaatar. Mark-recapture techniques (1,438 markings, 19,606 recaptures in total) and complementary methods were used. The density maximum was observed in July with 98 (1988); 169 (1989) and 94 (1990) individuals/ha and the population fluctuated by a factor of 7.4.

At the beginning of reproductive period the males disperse over a minimum distance of one female home range whereas the females do not migrate after winter. The typical mating system is promiscuity. Youngsters have been recorded from …

Biodiversity And Ecology Of Soil Oribatid Mites (Acari: Oribatida) In The Grassland Habitats Of Eastern Mongolia, Badamdorj Bayartogtokh

Erforschung biologischer Ressourcen der Mongolei / Exploration into the Biological Resources of Mongolia, ISSN 0440-1298

Composition, abundance, distribution, and diversity of oribatid mite communities were investigated at five study areas in Eastern Mongolia. A total of 88 species of oribatid mites were recorded from the studied areas. The largest number of species (51 spp.) was found in the habitats of river valleys, while the plain steppe which covers the largest area contained the lowest species richness (24 spp.). Three other sub-regions with similar landscape types show approximately the same species richness (39 to 45 spp.), although they are located relatively far from each other. The oribatid mite faunas of all sub-regions were essentially similar to …

Biotic Resistance To Invasion: Native Predator Limits Abundance And Distribution Of An Introduced Crab, Catherine E. De Rivera, Greg M. Ruiz, Anson Hines, Paul Jivoff

Environmental Science and Management Faculty Publications and Presentations

Introduced species frequently escape the natural enemies (predators, competitors, and parasites) that limit their distribution and abundance in the native range. This reduction in native predators, competitors, and parasites may result in ecological release in the introduced range. However, biological interactions also can limit the establishment and spread of nonnative populations. The extent to which such biotic resistance occurs is poorly resolved, especially for marine ecosystems. Here we test whether a native predator, the blue crab Callinectes sapidus, affects the abundance and geographic range of the introduced European green crab Carcinus maenas in eastern North America. Both crab species …