The Interface of Predation and Migration in Aquatic and Terrestrial Ecosystems

For the first ever joint meeting between the American Fisheries Society (AFS) and The Wildlife Society (TWS), we are excited to propose a special session that draws together research from both organizations. Migrating animals are ubiquitous across taxa and connect distant ecosystems. Many species are economically important (e.g. salmonids, water fowl, caribou, aphids) or endangered (e.g. elephants, butterflies, bats, sea turtles). Migrating animals can be important predators or prey, and their influence can extend into multiple ecological communities. Predator-prey interactions can influence survival, behavior, population dynamics, community structure, and ecosystem processes. This session aims to bring together scientists studying the interface of predation and migration across aquatic and terrestrial ecosystems. We hope to draw researchers studying diverse taxa, conducting studies at different scales, and asking complementary questions. Ultimately, we aim to clarify shared patterns and approaches seen in different study systems, build future cross-taxa collaborations, and improve our general understanding of predator-prey interactions in migrating animals. We have 10 confirmed and 4 tentative speakers already that span diverse migratory taxa. Confirmed Eric Palkovacs – introduction Ron Ydenberg – birds Mark Boyce – ungulates & carnivores Aaron Wirsing – bears & adult salmon Megan Sabal – juvenile salmon & conceptual Tom Luhring – lamprey Kevin Monteith – ungulates Michael Wagner – lamprey Bob Srygley – insects Jonathan Cohen – zooplankton Nathan Furey – fish and/or review Tentative Abby Nelson – ungulates & wolves Mike Melnychuk – juvenile salmon Mark Hebblewhite – ungulates & wolves

8:00AM Context-Specific Selection of Anti-Predator Tactics during the Return Migration of Sea Lamprey in Response to a Chemical Alarm Cue
  Michael Wagner, Thomas M. Luhring, Jason Bals, Gregory Byford, Trevor Meckley, John Hume, Mikaela Hanson
Near the conclusion of its life, the sea lamprey (Petromyzon marinus) undertakes a solitary nocturnal migration from offshore waters (Atlantic Ocean or Laurentian Great Lakes) into rivers to spawn. It permanently ceases feeding and does not exhibit natal philopatry. Rather, a symphony of odors reveal opportune habitats for locating mates and rearing offspring. Migration into spawning streams entails a rapid transition in both threat (the number and type of predators) and vulnerability to attack (narrow, shallow habitat). The location and immediacy of predator attack is revealed, in part, by the recognition of a damage-released alarm cue that is emitted from the tissue of wounded lampreys and induces anti-predator behavior. Here, we report the outcomes of a series of laboratory and field experiments designed to reveal how the presentation of the alarm cue (e.g. avoidable or unavoidable risk, equating to partial or complete mixing of the cue in the river discharge) regulates the expression of anti-predator tactics that minimize exposure to the risky area in three arenas: when entering the river mouth from offshore, when moving upstream low in the watershed, and when selecting a tributary for spawning at the confluence of two rivers high in the watershed.
8:20AM From Chemical Cue to Predator Avoidance: How Fish Kairomones Alter Vertical Migration in Marine Zooplankton
  Jonathan Cohen, Corie Charpentier
Chemical exudates from fish (kairomones) activate behavioral strategies for predator deterrence in their zooplankton prey. One such strategy is diel vertical migration, where zooplankton reside deeper in the water column during the day as a refuge from visual predators. For marine zooplankton, fish kairomones are thought to be aminosugar compounds derived from fish mucus. The proximate physiological mechanisms underlying behavioral alteration in marine zooplankton exposed to fish kairomones are becoming clearer. For the planktonic larval stages of benthic estuarine/marine crabs, fish kairomone exposure lowers the light intensity required to evoke swimming responses involved in diel vertical migration. This suggests crab larvae would reside deeper during the day with fish present. Light data and optical modeling show that in estuarine/marine habitats, small changes in depth can result in large changes in light intensity and therefore visibility to predators. Electroretinogram recording from compound eyes of larval crabs exogenously exposed to fish kairomones at concentrations which alter photobehavior shows that the sensitivity of retinal cells in eyes also increases, due in part to rapid changes in eye ultrastructure. This provides a mechanism for kairomone-induced behavioral change.
8:40AM An Escape Theory Model for Migrating Prey and an Experimental Test in Juvenile Salmon
  Megan Sabal, Joseph Merz, Suzanne Alonzo, Eric Palkovacs
Migrating prey are ecologically and economically important and encounter predators while traveling. Economic escape theory has been valuable in understanding behavioral responses of stationary prey under predation risk, however, current models are not applicable for actively migrating prey. We present a model variation that predicts how much risk migrating prey perceive as measured by their change in speed from engaging in antipredator behaviors. We applied the sensitization hypothesis to our model, which predicts that prey with more predator experience should change their speed more under predation risk. We tested model predictions using a behavioral assay with juvenile Chinook salmon (Oncorhynchus tshawytscha), which varied in their past predator experience. Hatchery salmon had the least predator experience, followed by wild salmon captured upstream (wild-upstream) and wild-salmon captured downstream (wild-downstream). We timed salmon swimming through a flume with and without predator cues. Both wild-downstream and wild-upstream salmon slowed down in response to predator cues, while hatchery salmon did not change speed. The magnitude of reaction to predator cues by salmon group followed the gradient of previous predator experience, supporting the sensitization hypothesis. Our study extends the scope of economic escape theory and improves general understanding of non-lethal effects of predators on migrating prey.
9:00AM Human Predation on Migratory Elk in Alberta
  Mark Boyce, Simone Ciuti, Dale Paton
Migrations of large ungulates are globally threatened in environments affected by increasing human disturbance, rising large carnivore predation, deteriorating habitat quality, and changing climate. We compared habitat selection, movement, and behavior of a large migratory herbivore while migrating through a heterogeneous landscape in spring and fall using GPS telemetry. We tested the hypothesis that fall hunting exacerbates the response of a large herbivore exposed to human disturbance while migrating through a road network. Elk (Cervus elaphus) selected greater forest cover, reduced movement rates, and avoided roads during fall-day than in any other season or time of day. We show that elk response to human predators was greater than to large carnivores both behaviourally and demographically. Elk spent more time feeding during spring migration compared to the fall migration and elk vigilance was >3 times higher in the fall hunting season. Our results provide insights into the effect of fear of humans on the ecology of both sexes of a migrating large herbivore when using stopovers. Such changes in behavior and stopover use might affect fitness by decreasing foraging, cause displacement from high-quality habitats, or affect the permeability of migration route stopovers.
9:20AM Habitat-Mediated Effects of Diurnal and Seasonal Migration Strategies on Juvenile Salmon Survival
  Michael Melnychuk, David Welch
Behavioral decisions during periods of vulnerability to predation risk, such as migrations during the juvenile life-history stage, may affect survival, and risk-reducing behaviors may be more important in some habitats than others. Using biotelemetry data, diurnal and seasonal riverine migration patterns of >3800 juvenile salmon were quantified across 12 watersheds to evaluate possible effects of migration timing on survival from lower rivers to coastal waters. In small, clear rivers most salmon avoided migrating during daylight hours and average survival of fish migrating at night. Conversely, in the large, heavily silted Fraser River neither preference for nocturnal travel nor effects of diurnal timing on survival were observed. Early ocean survival was also influenced by the timing of ocean entry, but in opposite directions: in the Fraser River, average survival for later migrants was nearly twice that of earlier migrants, likely related to seasonal increases in river flow; in smaller rivers, average survival for earlier migrants was 3-fold greater than survival for later migrants. Together, these results demonstrate that timing decisions affecting survival of juvenile salmon during their migration are likely mediated by landscape characteristics that plausibly influence the risk of predation.
09:40AM Break
1:10PM Complex Effects of Late-Summer Habitat Quality, Predation Risk, and Disease on Elk Pregnancy across the Greater Yellowstone Ecosystem
  Owen Bidder
Over recent decades in western North America, migratory elk populations have undergone a long-term decline in recruitment. In some areas, reduced pregnancy rates may have exacerbated these declines. Changing forage phenology and predation pressure are hypothesized to influence elk pregnancy, but few landscape-scale analyses are available. We sampled the pregnancy status of 1106 female elk at 25 sites across the Greater Yellowstone Ecosystem (GYE) over a 13-year period, assessed pregnancy rates, and evaluated both top-down and bottom-up influences on individuals’ probability of pregnancy. Our findings show that pregnancy rates are generally high across the GYE (x̅=82.4%), and that an individual’s probability of pregnancy is a function of both extrinsic and intrinsic influences. Specifically, early senescence of forage in autumn and the reproductive disease brucellosis negatively impacted the probability of individual elk pregnancy. Contrasting with previous studies, we found no evidence for effects of wolf predation risk, elk density or winter severity on the probability of pregnancy. Though we did not quantitatively evaluate the influence of pregnancy on recruitment, our findings suggest they are sufficient to maintain elk recruitment in the system. Nevertheless, the pregnancy rate in elk and other ungulates may serve more broadly as an indicator of significant influences on nutrition and demography of this important migratory species.
1:30PM Local and Landscape Drivers of Brown Bear Aggregation to and Predation in Salmon Spawning Streams in Southwestern Alaska
  Aaron Wirsing, Tom Quinn, Curry Cunningham, Jennifer Adams, Apryle Craig, Lisette Waits
After growing at sea for several years, Pacific salmon return to streams for spawning and then inevitably die. The great biomass of migrating salmon is consumed by a wide variety of organisms, but bears play an especially important role as predators and also by making uneaten salmon carcasses available to other organisms. Here, leveraging extensive data on brown bear (Ursus arctos) aggregation (2012-present) and predation (1990-present) along a series of sockeye salmon (Oncorhynchus nerka) spawning streams in southwestern Alaska, we show that (i) individual bears show fidelity to distinct stream (foraging) neighborhoods while targeting spawning salmon; and (ii) rates of bear predation within these foraging neighborhoods depend on both local stream characteristics (depth) and the density of salmon in nearby streams. These findings suggest that fluctuations in salmon availability are likely to be experienced asymmetrically by members of coastal bear populations, and that patterns of bear predation depend on salmon density at multiple spatial scales.
1:50PM What Can Radio Telemetry Reveal about Mormon Cricket Migration and Predation?
  Robert Srygley, Patrick Lorch
Mormon crickets are model organisms for understanding collective motion in animals. Grouping provides safety from predation, but grouping also has costs, including increased competition for food and risk of cannibalism. We investigated predation by digger wasps on collectively moving Mormon crickets as an additional cost to grouping. By radio-tracking migrating Mormon crickets released over three days, we found that digger wasps prey heavily on aggregated Mormon crickets leading to loss of safety from predation. Palmodes laeviventris paralyzed and buried 42% of tagged females and 8% of the males on the final day of tracking. A preference for females to provision their offspring make the digger wasps particularly effective at controlling Mormon cricket populations. The greater fat content and larger size of female Mormon crickets compared to males probably improves survival of wasps during diapause. Wasps may play an important role in causing density declines leading to periods where Mormon crickets are only found sporadically throughout their range. Wasp predation represents a cost to collective movement with results from this study suggesting that avoidance of this specialized predator should strongly select for Mormon cricket emigration from natal sites, adding to the threat of cannibalism as selective forces spurring collective motion.
2:10PM Every Fish That Dies Gets Eaten
  J.D. Wikert
Outmigrating juvenile salmonids in California’s San Joaquin Basin experience low survival. One suite of possible management actions includes efforts at reducing impacts from predators on these juvenile fish. Several studies have been undertaken on the Stanislaus River in an effort to understand factors influencing mortality in juvenile salmonids. Both flow and habitat have been identified as significant factors influencing mortality during rearing and migration of juvenile salmonids. A better understanding of relationship between flow, habitat, and predation will greatly assist in effectively managing limited resources to support self-sustaining populations of salmon and steelhead. Multiple factors influencing mortality will need to be addressed to achieve any lasting improvement in survival of juvenile salmonids. Come to the presentation for more detail on this important topic.
2:30PM How the Evolutionary Ecology of Avian Migration Is Shaped By Predation Danger
  Ron Ydenberg
Though acknowledged as potentially important, the effects of predators in the evolutionary ecology of avian migration has not been well-defined. Most effort has been directed to the energy and time considerations in acquiring the food necessary to meet migratory schedules. Migrants are often subject to predation, but the larger impact of predators may lie in selecting for traits that reduce the exposure or vulnerability of migrants to danger, and thereby lower the mortality rate. I review studies of western and semipalmated sandpipers (Calidris mauri, C. pusilla), both long-distance neotropical migrants, to illustrate how timing, speed, routing and other migratory traits are shaped by the danger posed by their predators, especially merlins (Falco columbarius) and peregrine (F. peregrinus). Both these falcon species also migratory, making migration a predator-prey game. The ongoing increase in the numbers of these and other raptors since the mid-1970s has made migration more dangerous for sandpipers and other avian migrants, and has exerted strong effects on their behavior and morphology.
2:50PM Refreshment Break
3:20PM Ecology of the Gauntlet: Lessons Learned for Predator-Prey Interactions during Salmon Smolt Migrations
  Nathan B. Furey, Scott Hinch, Arthur Bass, Eduardo Martins, Adam Kanigan, Kristi Miller
To better understand migration ecology, we studied the downstream of migrations of juvenile sockeye salmon (Oncorhynchus nerka) smolts at Chilko Lake, British Columbia, Canada. Chilko Lake supports one of the largest sockeye salmon populations in BC. Previous use of acoustic telemetry identified the first migratory segment, within the Chilko River, to be a high-risk landscape associated with poor survival. Bull trout (Salvelinus confluentus), a native char of conservation concern, opportunistically exploit the migration by binge-feeding on smolts. Molecular tools compared predated and non-predated smolts, and indicated that individuals infected with a specific virus experienced more than a ten-fold increase in predation risk by bull trout. Thus, predators may facilitate “migratory culling” within migratory populations. Pseudo-experimental releases of acoustic-tagged smolts revealed smolt survival through this high-risk landscape was dramatically increased when travelling downstream with large densities of co-migrant conspecifics. This result provides rare evidence for swamping to effectively reduce individual predation risks in a migrant animal. Telemetry also revealed bull trout to move in response to smolt migrations, providing potential evidence of “migratory coupling” between the migrant smolts and bull trout exploiting the prey pulse. These studies demonstrate important ecological links between diadromous migrants and consumers.
3:40PM When Migration, Nutrition, and Predation Collide
  Kevin Monteith, Vern Bleich, Tom Stephenson, Becky Pierce, Terry Bowyer
Migration is a profound life-history event exhibited by many taxa worldwide, especially those residing in seasonal environments. The sheer abundance of migratory compared with nonmigratory animals has prompted the notion that migration must often be a favorable behavioral tactic. Through long-term, individual based research in the Sierra Nevadas of California, we documented marked shifts in migratory segments of a population of mule deer that shares a common winter range. Between 1985 and 2005, the segment of the population that migrated to the west side of the Sierra crest declined from 87% to <50%. This marked shift occurred despite complete fidelity to summer ranges, and was instead linked to differences in demography. Survival of neonatal deer to 140 days was lower on the west side (0.13, SE=0.092) compared with the east side (0.44, SE=0.11). Partially additive predation by black bears was the likely explanation for the shifts in migratory tactics, even though west-side migrants enjoyed better nutrition. The results of our case study highlight the notion that the process of migration integrates large landscapes that may well yield a nutritional boon and ameliorate severe weather, but simultaneously integrates the interactive effects of predation wherever an animals path may lead them.
4:00PM Ideal Free Migration??? Testing for Density-Dependent Migration in a Partially Migratory Elk Population.
  Hans Martin, Mark Hebblewhite, Evelyn Merrill
What determines the proportion of migrants in partially migratory populations? Partial migration is thought to be maintained in a population through two mechanisms: 1) counteracting density dependence on migrants and residents; or, 2) conditional migration where individuals make the decision to migrate based on intrinsic or extrinsic factors. Thus, partial migration can be viewed as a form of habitat selection between different seasonal ranges, and our understanding of migration can be viewed as density-dependent habitat selection following the Ideal Free Distribution Theory (IFD). We assess the concept of ideal free migration using 18 years of elk data, including female and calf survival with known differences in predation risk and forage quality for migrant and resident summer ranges. We consider that partial migration is consistent with IFD if there is evidence for differential density dependence operating on the vital rates of migrants and residents. Additionally, we determine if switching is density dependent or conditional. Our study allows us to understand how changes in forage quality and predation risk on seasonal ranges affect the number of migrants in partially migratory populations and how changing proportions of migrants and residents explain population dynamics observed over the past 18 years.
4:20PM Predation Alters Aquatic-Terrestrial Exchange of Biomass and Nutrients.
  Thomas M. Luhring
Migratory prey species are often important vectors of biomass and nutrients between ecosystems and predation alters their physiology, the quantity of prey moving among ecosystems, and their subsequent distribution in the landscape. We explore the effects of predation on the movement of nutrients and biomass across the terrestrial-aquatic landscape with examples focused on amphibians with complex life histories (e.g., aquatic larva, terrestrial juveniles and adults). Namely, we use data drawn from mesocosm experiments where predators (aquatic newts) alter the abundance and size of anurans that metamorphose and move aquatically derived nutrients and biomass into the terrestrial environment. Furthermore, the stoichiometry of inputs into the aquatic system (ova) differs substantially from exports into the terrestrial system (juveniles). We derive a simple mathematical model based on equal movement of biomass and nutrients across system boundaries. We then incorporate life history strategies, ontogenetic stoichiometry, and predation effects to investigate how predators alter the net movements of different fluxes between two disparate systems.
4:40PM The Future of Migration and Predation
  Eric Palkovacs, Megan Sabal
This talk will tie together the main themes of the symposium into an integrated framework for understanding the role of predation in animal migrations. The fields of sensory ecology, behavioral ecology, population ecology, and evolutionary ecology all provide insights for how predators and prey interact in the context of migration. Integrating across study systems, subdisciplines, and scales of analysis can provide new insights into migration and predation. This concluding talk in the symposium will place each of the preceding talks into a general framework, allowing us to see the big picture of how predation shapes, and is shaped by, migration. Increasingly, humans are impacting animal migrations through modifications to habitat, introduced species, and by acting as predators ourselves. Securing the future of animal migrations will depend on understanding and managing these human influences.

Organizers: Eric Palkovacs, Megan Sabal

Location: Reno-Sparks CC Date: October 3, 2019 Time: 8:00 am - 5:00 pm