Storage effects in intermittent river ecology: implications for coexistence, biotic interactions and colonization dynamics Hydrobaenus sp. (Chironomidae) diapause in desiccation-resistant case Intro Thank you to VT and IRSTEA Photo of Hydrobaenus collected durng my MS project Ross Vander Vorste Virginia Water Resources Research Institute, Virginia Tech University Thibault Datry IRSTEA, Villeurbanne, France @RiversRossV Society for Freshwater Science 2016

Biodiversity and community assembly Environment Biotic interactions “Filters” Regional species pool Local community Dispersal Community assembly As a freshwater ecologist, I am interested in understanding what produces the vast amounts of biodiversity in freshwater ecosystems Also, the processes of community assembly or how local communities are formed from the regional species pool Here, shapes represent different species in the regional species pool and through processes such as dispersal and interactions with the environment and other bioto can come together to form a local community (Poff 1997 JNABS, HilleRisLambers et al. 2012 Annu. Rev. Ecol. Evol. Syst.)

Biodiversity and community assembly How is diversity maintained in a fluctuating environment? Harsh environmental conditions Environmental fluctuations Harsh We now know that the relative importance of these processes or filters change as the environment fluctuates, across a gradient from favorable to harsh conditions When you think about these harsh conditions such as fires floods and drying these conditions really test local communities, often removing many or most of the species inhabiting a local community So this brings up an important question “ How is biodiversity maintained in the face of harsh environmental conditions “ This is a question that a lot of scientists are asking themselves considering our changing climate Favorable Time

Storage effects can maintain species diversity Population growth during favorable environmental conditions is stored and buffers species from the negative effects of harsh conditions One way that biodiversity can be maintained is though storage effects What are storage effects? This is when population growth during favorable environmental conditions is stored and buffers species from the negative effects of harsh conditions (Chesson 2000 Annu. Rev. Ecol. Evol. Syst.)

Storage effects can maintain species diversity Population growth during favorable environmental conditions can be stored and buffer species from the negative effects of harsh conditions 1 Species have different responses to the environment Abundance High Low Water availability Species 1 Species 2 Storage effects can occur when species have different (Chesson 2000 Annu. Rev. Ecol. Evol. Syst.)

Storage effects can maintain species diversity Population growth during favorable environmental conditions can be stored and buffer species from the negative effects of harsh conditions 1 Species have different responses to the environment 2 Covariance between environment and competition Competition High Low Water availability (Chesson 2000 Annu. Rev. Ecol. Evol. Syst.)

Storage effects can maintain species diversity Population growth during favorable environmental conditions can be stored and buffer species from the negative effects of harsh conditions 1 Species have different responses to the environment 2 Covariance between environment and competition 3 Species traits limit the impact of the environment and competition the seedbank (Chesson 2000 Annu. Rev. Ecol. Evol. Syst.)

How can “storage” influence communities? Colonization dynamics 1 Early colonizing taxa can have priority effects

How can “storage” influence communities? Colonization dynamics 1 Early colonizing taxa can have priority effects 2 Biotic interactions Could reduce competition and predation pressure

How can “storage” influence communities? Colonization dynamics 1 Early colonizing taxa can have priority effects 2 Biotic interactions Could reduce competition and predation pressure 3 Species coexistence Trade-off between resistant and resilient strategies

How can “storage” influence communities? Colonization dynamics 1 Early colonizing taxa can have priority effects 2 Biotic interactions Could reduce competition and predation pressure 3 Species coexistence Trade-off of resistant and resilient strategies Examples in the literature: ? Durden images Adler et al. 2006 PNAS Angert et al. 2009 PNAS Usinowicz et al. 2009 ECOLOGY

Intermittent rivers as a model system Environmental fluctuations Roubion River, France Before drying During drying Bertrand Launay

Intermittent rivers as a model system Environmental fluctuations Found globally and increasing in abundance Danube (Germany) Manganui (NZ) Tete (Mozambique) McMurdo Valley (Antarctica) Kapoeta (Soudan) Rio Grande (US)

Intermittent rivers as a model system Environmental fluctuations Found globally and increasing in abundance Threatened by climate change, water abstraction and other human activities Pete McBride Colorado River, USA Chandravir Singh Narmada River, India

Invertebrate storage in intermittent rivers Hyporheic zone use during drying Hyporheic zone S. Luk Gammarus pulex (Gammaridae) Leuctra sp. (Leuctridae) Baetis sp. (Baetidae)

Invertebrate storage in intermittent rivers Hyporheic zone use during drying Hyporheic zone S. Luk Gammarus pulex (Gammaridae) Leuctra sp. (Leuctridae) Baetis sp. (Baetidae) Resistance forms prevent desiccation Eggs, body armoring (cases), diapause/dormancy Mesocapnia arizonensis (Capniidae) M. Bogan M. Billard Hydrobaenus sp. (Chironomidae) Stenophylax latipenis (Limnephilidae)

Storage effects and colonization dynamics No Non-dispersing colonizers Dispersing colonizers Before During After Vander Vorste et al. 2015 FWB

Storage effects and colonization dynamics No Non-dispersing colonizers Dispersing colonizers Before During After Invertebrates from the seedbank colonize first and could have ‘priority’ over dispersing colonizers

Cybister tripunctatus Storage effects and biotic interactions Large predator Prey Before During After Cybister tripunctatus (Dytiscidae) Predator Gammarus pulex (Gammaridae) Prey Prey can use hyporheic zone to avoid biotic interactions and drying can remove top predators

Storage effects and species coexistence Resilient species Resistant species Before During After Invertebrate storage can lead to establishment of ‘early’ and ‘late’ season communities

Key research questions Colonization dynamics Are there priority effects related to colonization via invertebrate storage? Study design: species additions to mimic ‘early’ and ‘late’ arriving taxa Mesocosm experiments

Key research questions Biotic interactions Does invertebrate storage reduce competition and predation pressure during harsh environmental conditions? Study design: measure biotic interactions w/ and w/o hyporheic zone Manipulative field experiments

Implications for IRES management Species coexistence Can invertebrate populations increase from low population size in the presence of a competing taxa? Study design: long-term population dynamics Field observations Population modeling Abundance Species 1 Species 2 Time

Broader implications for freshwater ecology Temporal vs spatial dispersal Storage could reduce connectivity among meta-communities Alteration of gene flow among populations Intermittent river management Increased duration will reduce importance of storage effects Importance of protecting invertebrate storage

In summary @RiversRossV Contact: ross.vandervorste@vt.edu Similar to terrestrial systems, storage occurs through the combined use of the hyporheic zone and desiccation-resistance forms by invertebrates in IRES. Circumstantial evidence suggests that storage influences colonization dynamics, biotic interactions and species coexistence. Research should be directed towards addressing several key research questions related to storage effects to advance IRES ecology.