Drift • downstream transport of benthos in water column • common drifters Ephemeroptera (Baetis), Chironomidae, Simuliidae, some Plecoptera and Trichoptera, Gammaridae diatoms larval vertebrates • ecological significance • mode of dispersal, emigration (Waters 1972) • food resource for drift-feeding fish and large filter-feeding invertebrates • Waters (1965): behavioral drift, constant drift, catastrophic drift Drift You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) • mesh size • fraction of benthos difting • at any moment - 0.01 - 0.5% • over 24h period - up to 100 × density • drift density ~ 100-1000 ind./100 m3 • drift rate ~ 104-105 ind./24 h Drift Amount of drift You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Colonization cycle (Müller 1954) • larval populations move downstream • Upstream larval movement of larvae ca 30% (Elliott 1971) • compensations by upstream flight of adults • egg-bearing females fly upstream for oviposition (Roos 1957) • confirmed by number of studies (e.g., Otto & Svenson 1976) • but Elliott (1967): flight of ETP according to the wind direction Drift You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Drift Colonization cycle II You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Drift distance • return to substrate • experiments with live vs dead specimens • traveling distance – nightly up to 75 m, life-time up to 10-15 km? • little evidence for pools to trap drift Drift You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Behavioral drift • nocturnal activity • one or two peaks: after dusk, before dawn • light intensity treshhold ~ 1 lux • „risk of predator“ hypothesis (Allan 1978) • Chironomidae – aperiodical • Diatoms, water mites – daytime drift • Palmer et al. (1992): strong nocturnal drift of copepods, oligochetes, rotifers and small chironomids Drift You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Behavioral drift II Drift • exogenous vs. endogenous control • negative phototaxis • Baetis: constant light → no dri • constant darkness: nocturnal periodicity lasts for ca a week You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Drift Drift as predation avoidance • Allan (1978) – insect larvae drift more at night and are larger • McIntosh & Peckarsky (2006) – night drift induced in Ephemeroptera in a fishless stream after introducing fish odor You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Drift to search for food sources • Kohler (1985) How does drift respond to starvation, access of food, and algal patchiness? Baetis enter drift to find food Drift You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Cost and benefits of drift • Advantages • finding food – increased fitness • avoid tacticle invertebrate predators (Baetis) • Disadvantages • landing in poor habitat • exposure to visual drif-feeding predators (% zero fitness) • Ecological rule – minimizing „µ/g“ µ ... mortality risk g .... growth rate • Production compensation model (Waters 1961) – drift represents the production exceding the carrying capacity, entry to drift is disadvatageous, upstream movement unnecessary, drift low if the population under carrying capacity • Hildebrand (1974) – drift is a constant % of benthic density Drift You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Predation • ubiquitous • „key stone predation“ (Paine 1966, 1969, Allan 1982) • effects • reduction of abundance, elimination of species • restrictions on habitat use and foraging efficiency • adaptation through natural selection • cascade of interactions in trophic webs • changes in energy pathways • predator preference • prey vulnerability Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Trophicguildsofstream fishes Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Fish predators • vision, olfaction • bottom vs. midwater dwellers • bottom vs. drift feeding • adaptations of mouth, gill arches, fins • most studied: salmon and trout • strong predictors: fish abundance and size • predator size vs. prey size Predation Salmo salar You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Size preference in fish Predation • with increasing prey size • predation intensity increases • reaction distance increases Insect length (mm) You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Prey choice in fish • gut content vs. prey community composition • „availability factor“ (Allen 1941) • diet composition resembles the composition of fauna • common items over-represented • availability vs. true selection • field vs. laboratory studies • specialization on the most frequently feeded prey Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Learned specialization • predatory behavior changes with experience • increases rates of predation/foraging efficiency • „training bias“ • variation in individual feeding responce (Bryan & Larkin 1972) • capture rate varies with hunger level Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Energy maximization Predation • searching, handling • energy gain = • optimal prey size • rejection of superoptimal prey • no upper limit to prey size in nature (optimal prey size for a 20 cm salmon/trout: 10-12 mm) You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Influence of light on predation by fish • treshhold for effective visual location of prey ~ 0.1 lux • role of shading Predation pstruh žlutohrdlý You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) PredationInvertebratepredators You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Invertebrate predators • Pecarsky (1982,1984) • mechanical, visual, chemical detection, and their combinations • functional groups by Cummins (1973): • engulfers • piercers (Athericidae, some Chironomidae and Hemiptera) • means of hunting • sit-and-wait • searching • combinations of both • occasional predation Predation Dinocras cephalotes (Sjöström 1985) Ryacophila nubila (Otto 1993) Unionicola crassipes (Proctor & Pritchard 1990) You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Prey preference • gut analyses, head width mesurement • good correlation of proportion of prey in gut content and faunal community • average size of prey increases with increasing size of predator • diet change during development (e.g., stoneflies – Allan 1982) • size refuge Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Prey availibility, predator aggregation, and body size relationships • prey availibility – may override differences between predators in foraging mode → dietary overlap • patch use • aggregation of predators in patches of high prey density – correlative and experimental studies • e.g. Plectrocnemia conspersa (Hildrew & Townsend 1980) • absence of aggregative behaviour in predacious stoneflies (Peckarsky & Dodson 1980, Peckarsky 1985) • body size relationship - mutual predation and canibalism among predator species (Woodward & Hildrew 2002) Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Dietary overlap in invertebrates • small predators – narrow niche • niche overlap highest when predator sizes strongly overlapped • niche overlap decreased with increasing difference in predator size Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Predation rate in invertebrates Predation • predation rate increases with increasing prey density (functional response curve) increasing predator size • predation rate decreses before emergence and molting with satiation with habitat complexity and presence of refuge • little or no evidence for the role of learning and experience You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Prey vulnerability • mobility highly mobile prey (e.g., Baetis) is vulnerable to sit-and-wait predators but can escape from large searching predators (overestimation of predation rate in cage experiments) • anti-predator adaptations • some reduce the likelihood of encounter • fixed – protective armor, nocturnal activity, case building • induced – escape after encounter, visual contact or smell perception – different habitat use (Gerridae, Orconectes propinquus) • trade-off between minimizing predation risk and maximizing food aquisition Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Alternative predator avoidance (Peckarsky 1996) Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Effects of predation on prey populations • inverse relationship between piscivores and their prey • different relationships for invertivores • inverse correlation between fishes and invertebrate predators (Hildrew 1984) • no difference in invetebrate abundance between trout and troutless stream sections (Edwars 1986) • only Baetis abundances higher in troutless stream (Meissner & Muotka 2006) • manipulations of fish abundance using cages – different or no effect on invertebrate abundance • total prey consumption by trout ~ all available production (Allan 1983, Huryn 1996) • invertebrate predators usually consume less production than fish • when fish absent, invertebrate predators consume all secondary production at lower trophic levels Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Indirect effect on predation • predator avoidance → reduc on of fitness • predator risk reduces foraging • Baetis and stoneflies with glued mouhtparts in microcosmos (Peckarsky et al. 1993) • inducible life history shift • Baetis had faster maturation at smaller body size as reaction to trout odor (Peckarsky & McIntosh 1998) • drift as anti-predatory adaptation Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Trophic cascades Predation • influence of top predator on the whole food web • increase of algal abundance after reduction of grazers • algal blooms in New Zealand streams after introduction of non-native trout which excluded weaker competitor fish of native fam. Galaxiidae (Huryn 1996, Townsend 2003) • reduction of Lestidae → increase of Chironomidae → decrease of algae; fish removal → increase of algae • suppression of cascade if modest predatory effect– e.g. trout feeds mainly on terrestrial insect infall (Nakano et al. 1999) You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Predation as disturbance • intermediate disturbance hypothesis • equilibrium vs. non-equilibrium communities Predation You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Competition • shared limited resources • competition usually assymetrical • exploitative competition • interference competition – e.g. Simullidae vs. Blephariceridae, Hydropsyche siltalai (Englund 1993) • diffuse competition • niche specialization: habitat, dietary or temporal segregation (Schoener 1074) • correlative studies, field and laboratory experiments • many studies on algae indicate competition (for light and space) • competition in filter feeders - Hydropsychidae • resource partitioning: food particle (Wallace et al. 1977), microhabitat (Hildrew & Edington 1979, longitudinal distribution (Lowe & Hauer 1999), life cycle (Mackay 1977) • but no evidence that food and space are limiting Competition You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Competition in grazers • combination of exploitative and interference competition • snails (Hill 1992) • Glossosoma – dominant grazer, robust and slow • vs. Baetis (Kohler 1992) • collapse induced by microsporidian pathogen (Kohler & Wiley 1997) Competition You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com) Competition You created this PDF from an application that is not licensed to print to novaPDF printer (http://www.novapdf.com)