If the Time is Right: Phenology Match and Mismatches Across Ecosystems

Timing is everything. Climate change will likely shift the timing of ecological dynamics within habitats, which may spillover to influence across-ecosystem subsidies and interactions. Across-ecosystem subsidies can often be critically important for unproductive habitats. As a classic example, ocean-grown salmonids breeding in streams can be a boon for freshwater habitats and riparian consumers. However, as the timing of key ecological events shift in some habitats but not others, these across ecosystem subsidies may increase, decrease or be under-utilized. In the salmon example, will bears and other terrestrial consumers be ready to hunt for spawning salmon if the timing of the migration shifts? Will freshwater scavenging invertebrates be at a life stage when they can utilize decomposing carcasses? These timing shifts have the potential to influence interactions between micro-habitats (e.g., littoral and pelagic zones of lakes, canopy levels in the forest), across ecosystems (e.g., marine-terrestrial boundaries), and between fisheries and wildlife. This session seeks to address how within- and across-ecosystem subsidies will change due to climate change induced phenology shifts. What systems are resilient to these shifts? Will invasive or native species be more likely to adapt to subsidies with altered phenologies? Can we predict how these shifts will influence population dynamics in threatened species, or which species may become threatened as key subsidies are no longer available?

8:00AM Phenology of across-Ecosystem Subsidies: Theory and Introduction
  Suzanne Kelson, James Simmons, Sudeep Chandra
Timing is everything. Climate change will likely shift the timing of ecological dynamics within habitats, which may spillover to influence across-ecosystem subsidies and interactions. Across-ecosystem subsidies can be critically important for unproductive habitats. As an example, ocean-grown salmonids breeding in streams can be a boon for freshwater habitats and riparian consumers. However, as the timing of key ecological events shift in some habitats but not others, these across-ecosystem subsidies may increase, decrease or be under-utilized. In the salmon example, will terrestrial consumers be ready to hunt for spawning salmon if migration timing shifts? Will freshwater scavenging invertebrates be at a life stage when they can utilize decomposing carcasses? These timing shifts have the potential to influence interactions between micro-habitats (e.g., littoral and pelagic zones of lakes, canopy levels in the forest), across ecosystems (e.g., marine-terrestrial boundaries), and between fisheries and wildlife. This session seeks to address how within- and across-ecosystem subsidies will change due to climate change induced phenology shifts. This presentation will introduce the theory behind why the timing of subsidies may be changing, and how they will effect recipient ecosystems and species, and introduce the systems where we will explore this phenomenon in this symposium.
8:20AM The Effects of the Timing and Duration of the Resource Subsidy on Stream Ecosystems
  Takuya Sato, Rui Ueda, Gaku Takimoto, Rana El-Sabaawi, John Richardson
Accumulating evidence has suggested that resource subsidies are temporally variable; e.g., timing, duration and magnitude. However, few studies have examined empirically how such temporal attributes are important in driving consumer populations, including fishes. In temperate forest-stream ecosystems, seasonal emergences of terrestrial arthropods and their nematomorph parasites synergistically determined the duration (pulsed vs. prolonged within a season) and seasonal timing (early vs. late in a growing season) of the terrestrial invertebrate inputs from forests to streams. In those systems, the prolonged-subsidy allowed larger salmonid fish to effectively monopolize the subsidy which resulted in creating a more size-varied population structure, compared with the pulsed-subsidy. On the other hand, salmonid fish exhibited a higher numerical response to the subsidy occurring early in the growing season than late-subsidy, with timing-dependent life history adoptions and diversity. While global warming is well-known to advance peak timing of the growing season, it also leads to longer growing seasons. Our studies suggest that if the terrestrial invertebrate subsidy becomes advanced and prolonged under climate changes, consumers (such as fishes) may increase in abundance, which would in turn cause stronger trophic cascades in recipient ecosystems.
8:40AM Ecological Interactions Change Direction and Magnitude at Different Time Scales in the Hokkaido Stream-Forest Ecosystem
  Amy M. Marcarelli, Colden V. Baxter, Joseph Benjamin, Yo Miyake, Masashi Murakami, Kurt Fausch, Shigeru Nakano
Experimental and theoretical studies often yield conflicting predictions about interactions in food webs. Theoretical studies suggest that fluxes of terrestrial invertebrates to streams should lead to apparent competition, where subsidized fish consumers increase their foraging of aquatic invertebrate prey. However, short-term experiments in Horonai Stream, Hokkaido demonstrated that terrestrial prey instead buffered aquatic invertebrate prey from fish predation (apparent mutualism). An ecosystem-level synthesis of material fluxes, production, and trophic basis of production among fish and their prey in this stream revealed that more than half the production of the three resident salmonids was derived from terrestrial prey, consistent with previous comparative and experimental studies. Nevertheless, comparing trophic fluxes to the organic matter budget also revealed that fish consumed 98% of annual aquatic invertebrate production. Hence, although short-term experiments indicated that the terrestrial prey subsidy resulted in apparent mutualism during summer, this analysis showed that inputs of terrestrial prey boost production of insectivorous fish during the summer, which in turn consume most aquatic invertebrate production annually, a clear case of apparent competition. Our analysis provides strong evidence that ecological interactions can be dynamic, so that interactions revealed by short-term experiments can change direction when measured over longer time periods.
9:00AM Rapidly Changing Mosaic of Aquatic and Terrestrial Resources in Floodplain during and after a Snowmelt
  Hiromi Uno, Naoki Yui, Wataru Mamiya, Rei Sakai, Shunsuke Utsumi, Osamu Kishida, Yoichiro Kanno
Aquatic environments on floodplains rapidly change as the discharge decreases and the water recede during and after a snowmelt period. Various aquatic organisms such as aquatic insects, planktons and tadpoles sequentially bloom in such temporal aquatic habitats on the floodplain. At the same time, leaves sprout from riparian trees and terrestrial insects grow on these trees. Both the sequentially blooming aquatic organisms and rapidly growing terrestrial insects that fall in the water provide important resources to aquatic predators such as salmonid fishes. On a floodplain, where the geological structures form complex mosaic of aquatic and terrestrial environments, the availability of the aquatic and terrestrial resources and respective timings of their availability varies spatially. Our surveys on aquatic communities and gut contents and growth measurements of salmonid fishes on a floodplain in Uryu research forest, Hokkaido, Japan during and after snowmelt periods elucidate the spatial structures of the temporally entangled aquatic and terrestrial food webs on a floodplain.
9:20AM Asynchrony of Insect Emergence across a River-Floodplain Mosaic and Consequences for Insectivore Diversity
  Jade Ortiz, Colden V. Baxter
Emergence of adult aquatic insects constitutes a resource flux that can influence a suite of terrestrial insectivores, and the relative importance of emergence pulses to recipient food webs may be determined by their timing and duration. Spatial heterogeneity may play a critical role in mediating the availability of these subsidies by creating patchiness, not just in the magnitude of these fluxes, but in their temporal dynamics. Different habitats may yield complementary or supplementary emergence patterns, and predator mobility likely mediates their ability to capitalize on such fluxes. We conducted a year-round study of emergence across a mosaic of 7 habitats that varied in physical characteristics within the Snake River-floodplain in southeastern Idaho. We evaluated the degree of synchrony in the spectra of emergence from these habitats, considering the contributions habitat heterogeneity, life-history variation, and composition of the insect community have on those temporal dynamics. We also investigated implications of emergence asynchrony for insectivore biodiversity. As insectivore communities associated with each habitat patch were combined into successively larger and more complex metacommunities, we observed that richness increased to create a more diverse assemblage than was found in any habitat alone. These findings further elucidate potential consequences of river-floodplain homogenization for biodiversity.
09:40AM Break
1:10PM Emergence Phenology of the Giant Salmonfly and Responses By Birds in Idaho River Networks
  Colden V. Baxter, McKenna M. Adams, David Delehanty
Emergence of adult aquatic insects from rivers depends on water temperature, and its timing influences this ephemeral but often critical resource for terrestrial insectivores like birds. Spatial heterogeneity in riverine habitat could mediate this timing, with consequences for predators, but this is poorly understood. We investigated emergence phenology of the giant salmonfly at three spatial scales in two Idaho river networks, and studied the influence of tributary confluences on this timing, along with associated bird responses. At the basin-scale, salmonfly emergence timing was patchy (varying from May-June), whereas within sub-drainages, emergence followed a downstream-to-upstream pattern. At the scale of reaches, thermal discontinuities created by 10 major tributary confluences created asynchrony (1-6 days separation) in emergence among the 20 reaches bracketing these confluences. We observed 10 bird species that captured salmonflies, some (e.g., Lewis’s Woodpecker, Western Tanager, American Dipper) captured large numbers, and some fed them to nestlings. Emergence asynchrony created by tributaries was associated with shifts in bird abundance and diversity; both nearly doubled, on average, during salmonfly emergence. Thermal heterogeneity in river networks may create asynchrony in aquatic insect phenology, prolonging the availability of this pulsed prey resource for insectivorous birds during key breeding times.
1:30PM Earlier Nesting By a Generalist Predatory Bird Is Associated with Human Responses to Climate Change
  Shawn Smith, Karen Steenhof, Chris McClure, Julie Heath
Warming temperatures are associated with changes in the phenology of growing seasons, prey abundance, and specialist predators, but little is known about how generalist predator respond to shifts in prey. We studied whether advancement in nesting phenology of a generalist predator, the American kestrel (Falco sparverius), was associated with shifts in growing seasons and prey abundance, in a mosaic habitat in southwestern Idaho from 1992-2015. We examined the relationship between remotely-sensed normalized difference vegetation index (NDVI) and small mammal abundance, used NDVI to estimate the start of the growing season (SoGS) in irrigated and non-irrigated lands, tested whether SoGS predicted kestrel nesting phenology, and examined relationships among irrigated SoGS, weather and crop planting. NDVI and small mammal abundance were positively correlated and NDVI-estimated SoGS advanced significantly in irrigated lands but not in non-irrigated lands. There was a positive relationship between the advancing kestrel nesting phenology and the SoGS in irrigated lands but not in non-irrigated lands. Crops were planted earlier following warmer winters which likely caused earlier abundances of prey items leading to earlier kestrel nesting phenology. This is one of the first examples of an association between human adaptation to climate change and shifts in breeding phenology of wildlife.
1:50PM River Hydrology and Food Web Subsidies Under Global Change
  Kirk Winemiller
A global comparison of food web dynamics in rivers and estuaries reveals important spatial food web subsidies that derive from lateral and longitudinal exchanges of resources and consumers that are driven by hydrology. Flow pulses that submerge riparian habitats provide fishes with access to food resources of terrestrial origin and stimulate aquatic production that supports fish recruitment and growth. In the tropics, most fishes have synchronous spawning during the onset of the annual flood pulse. In temperate regions, many fish species similarly spawn during spring or summer during windows of time with appropriate temperature and hydrology. Migratory fishes move hundreds to thousands of kilometers longitudinally to spawn during high flow pulses, and some of these species have been shown to have strong top-down or bottom-up effects on food web dynamics in receiving ecosystems. In estuaries, pulsing freshwater inflows induce shifts in faunal composition and lateral and longitudinal exchanges of food resources and consumers. Evidence reveals that changing patterns of precipitation, land use and water diversion along the Gulf of Mexico and Brazilian Atlantic coasts and the Amazon, Mekong and Okavango/Zambezi basins are shifting the timing of flow pulses and food web subsidies with likely negative consequences for fish production.
2:10PM Simulated Climate Change Scenarios Indicate Remarkable Changes in Fisheries Due to a Mismatch between Temperature and Flooding Regimes
  Eduardo R. Cunha, Kirk O. Winemiller, Pitagoras A. Piana, Angelo A. Agostinho, Luiz Gomes
Climate change scenarios suggest shifts in precipitation patterns, changing flood regimes in floodplain ecosystems. Changes in flood timing may change fish population dynamics because of phenology mismatches. We used an individual-based model that simulates fish population and food web dynamics to test whether shifts in flood regime affect fisheries in the last major un-dammed reach of the Upper Paraná River in Brazil. The model simulates environmental conditions and food web interactions on a daily time step in response to hydrology and temperature regimes. The model incorporates general functions for biological processes and functional traits of species to simulate organism performance and population dynamics. We set the rules for individual fish feeding, growth, reproduction, and mortality based on conditions in its local environment. We simulated different scenarios of hydrology shifts and evaluated outcoming patterns of fish biomass. We found, that shifts in the hydrologic cycle lead to large changes in fisheries because of reduced fish recruitment. This is mostly because shifts in hydrology lead many fish species to spawn late, leading to intensified predation of early developmental stages due to increased food web interactions in response to temperature peaks. Such outcomes match general predictions based on consolidated literature about these ecosystems.
2:30PM Shifts in Phenology of the Spring Spawning of Adult Alewife (Alosa pseudoharengus): Impacts of Climate and Population Recovery
  John Sheppard, Rebecca Dalton, John T. Finn, Adrian Jordaan, Michelle D. Staudinger
The timing of biological events in many species, such as migration and reproduction, is shifting because of climate change. Anadromous fishes are particularly susceptible to these shifts when transitioning between marine and freshwater habitats to spawn and during egress. We determined the extent of phenological shifts in the timing of adult migration in alewife in twelve coastal streams along coastal Massachusetts. Migration timing was evaluated across coastal streams relative to regional-scale seasonal environmental predictors including spring and fall transition timing, winter duration, sea surface temperature (SST), as well as the North Atlantic Oscillation (NAO) and Gulf Stream indices. The direction and magnitude of phenological shifts were variable among streams with an overall trend towards earlier initiation dates, and because shifts in run end dates did not change, this resulted in longer run duration. We found that higher spring minimum SST, more positive winter NAO, and later fall transition dates best predict run initiation. Our results suggest shorter, wetter-winters and milder winter and spring temperatures result in earlier adult migration. Future analyses focusing on population and site-specific influences of migration are still needed to understand how climate change is interacting with other anthropogenic drivers of change to manage those impacts.
2:50PM Refreshment Break
3:20PM Meeting in the Middle: Resource Tracking of Freshwater Prey Subsidies By an Estuarine Consumer, Common Snook in the Florida Everglades
  Jordan Massie, Rolando Santos, Natasha Viadero, Ross Boucek, Jennifer Rehage
Movement among habitats is often driven by shifting resource availability, and can occur in response to cues such as fluctuating freshwater inflows in coastal systems. Movements of consumers into foraging areas provide vital resources that increase fitness, yet hydroclimatic shifts may influence the movements of both predators and prey, resulting in a potential mismatch of resources. Here, we examine how seasonal coast-to-headwater movements of the recreationally important fish species Common Snook, Centropomus undecimalis, align with the presence and density of prey subsidies concentrated into river channels by marsh drying in Everglades National Park (ENP), FL. We draw on long-term datasets of prey abundance and acoustic telemetry data of Snook movements to examine how fluctuations in freshwater inflows to the coast, including alterations introduced by extreme events (hurricanes, droughts), influence the timing and size of the marsh prey subsidies. Such events can provide insight into how fish communities may respond to climate change. ENP is the focus of large-scale restoration efforts that seek to restore freshwater flows that have been reduced by land use change, and research on the hydrologic conditions required to maintain balance between predator movement and prey availability is crucial to maintaining both biodiversity and economically important fisheries.
3:40PM Predator-Mediated Effects of Drought Associated with Poor Reproductive Success in a Nocturnal Seabird in a Cross-Ecosystem Cascade
  Sarah Thomsen, David Green
Despite the profound impacts of drought on terrestrial productivity in coastal arid ecosystems, only a few studies have addressed how drought can influence ecological cascades across ecosystem boundaries. In this study, we examine the consequences of the timing and pattern of rainfall pulses and drought that subsequently impact the breeding success of a threatened nocturnal seabird, the Scripps’s Murrelet (Synthliboramphus scrippsi). On an island off the coast of southern California, the main cause of reduced nest success for one of their largest breeding colonies is egg predation by an endemic deer mouse (Peromyscus maniculatus elusus). Mice on the island have an opportunistic diet of primarily terrestrial sources, but drastic declines in terrestrial productivity from drought could increase their reliance on marine resources, including murrelet eggs. We compiled data on terrestrial and marine productivity between 1983-2013 to determine how conditions in these ecosystems influence murrelet nest success. We found that the severity of drought had the strongest negative impact on murrelet nest success. Nest success was much higher under normal or high rainfall conditions, and was highest only when oceanic conditions were also favorable to murrelets. Therefore, the more frequent and severe drought that is projected for this region could lead to an increased risk of murrelet population decline on this island. Our study highlights the need for understanding how species interactions will change through the effects of altered rainfall regimes under global change.
4:00PM Assessing the Adaptive Capacity of Incubating Common Eider Ducks to Novel Polar Bear Predation
  Christina Semeniuk, Cody Dey, Grant Gilchrist
Climate change is leading to the loss of Arctic sea-ice and increases in polar bear (Ursus maritimus) predation of seabird nests. How this changing predator-prey relationship will impact polar bear and seabird populations is unclear. We have been conducting field studies and building predictive models to understand the impact of polar bear predation on populations of northern common eiders (Somateria mollissima borealis) in the Canadian Arctic Archipelago. Our studies suggest that polar bear predation of common eider nests will increase as sea-ice continues to decline. In response, eider hens will nest in smaller, more dispersed colonies to avoid polar bear predation. Additionally, we find that common eider population sizes should remain stable over the next 25 years because climate-driven increases in breeding propensity may compensate for increased nest predation. Together, these results suggest that northern common eider populations may be resilient to increasing polar bear predation, however changes in the spatial distribution of nesting females may make it harder for northern people to harvest eggs and down from eider colonies.
4:20PM Changing Sea Ice Phenology Triggers the Emergence of Divergent Behavioral Types in Polar Bears from Alaska’s Beaufort Sea
  Todd Atwood
The Earth has warmed by >1° C over the last 100 years, with the most pronounced warming occurring in the Arctic. Increasing air and sea temperatures have triggered changes to the marine ecosystem via declines in sea ice extent and volume. These changes have altered the phenology and character of ice habitats used by marine mammals. Species can respond to fluctuating environmental conditions by modifying their behavior, provided they possess sufficient phenotypic plasticity. If conditions are progressive, regime shifts can occur causing some behavioral adjustments to become fixed and lead to the entrenchment of distinct behavioral types. Here, we describe how changes in sea ice phenology have driven the emergence of divergent behavioral types for polar bears (Ursus maritimus) from Alaska’s southern Beaufort Sea (SB). While the majority of SB bears remain with the sea ice year-round, a growing proportion of the subpopulation now spends summer and fall on land. While on land, polar bears feed on terrestrial-based foods and are exposed to a broad array of stressors─ including those associated with increasing anthropogenic activities. We discuss how these across-ecosystem (i.e., marine-terrestrial) subsidies and interactions are affecting polar bear fitness, population dynamics, and the potential for human-polar bear interactions.
4:40PM Seasonal Variation in Diet, Microbiome, and Metabolome of Two Species of Woodrat across a Sharp Ecological Gradient
  Danny Nielsen, Kaitlin Ochsenrider, Lora Richards, Chris Jeffrey, Marjorie Matocq
Mammalian herbivores must balance nutritional requirements while limiting exposure to toxic plant secondary compounds (PSCs). Therefore, mammalian herbivores must adapt to changes in dietary resources. Seasonal variation in food plant availability may result in corresponding changes in the diets of wild herbivores, as well as the microbiome and chemical metabolome. We study two species of woodrat (genus Neotoma) that hybridize across a sharp ecotone in southern California where Mojave Desert scrub transitions to southern Sierra Nevada woodland. We present findings from a study in which we sampled woodrat fecal pellets across a seasonal gradient to characterize phenological patterns in woodrat diet, microbiome, and metabolome. We found that woodrats maintained distinct diets on either side of the ecotone and that diet shifted seasonally in accordance with availability of annual forbs. Corresponding changes in microbiome and metabolome also occurred that correlated with seasonal changes in diet. Our findings indicate that mammalian herbivores modify their diet in response to available dietary resources and that these shifts co-occur with changes in the gut microbiome community and chemical metabolome. Our findings provide insight into how herbivores acclimate to changes in food availability, which may help guide wildlife and habitat management efforts under changing environmental conditions.

Organizers: Suzanne Kelson, James Simmons, Sudeep Chandra
Supported by: Suzanne Kelson , James Simmons, Sudeep Chandra

Location: Reno-Sparks CC Date: October 1, 2019 Time: 8:00 am - 5:00 pm