Exploitation: Predation, Herbivory, Parasitism & Disease • Terms Herbivore œ consume plants but usually do not kill them Predator œ kill and consume other organisms Parasites œ live on the tissue of host organisms, usually weakens them but does not usually kill them Parasitoid œ usually kill their host, seen mostly in organisms with rapid life cycles (insects and mites) Pathogens œ induce disease in their hosts 1 Exploitation: Predation, Herbivory, Parasitism & Disease • Parasites and Pathogens That Manipulate Host Behavior œ Parasites That Alter the Behavior of Hosts œ many parasites alter the behavior of the host to spread the parasite further • Acanthocephalans (SpineyHeaded Worms) œ Infect amphipods œ Alter amphipod behavior to make it more likely for them to be ingested by beaver, ducks and muskrats » Uninfected amphipods demonstrate negative phototaxis » Infected organisms demonstrate positive phototaxis œ this brings them closer to the surface of the water and makes them more likely to be eaten 2 Exploitation: Predation, Herbivory, Parasitism & Disease • Janice Moore (1983, 84) œ observed a complex relationship between three organisms: œ An Acanthocephalan, Plagiorhynchus cylindricans œ A terrestrial isopod, a pill bug Armadillidium vulgare, this organism serves as the intermediate host for Plagiorhynchus œ The European Starling, Sturnus vulgaris Initial observations showed that only 1% of pill bugs were infected whereas 40 % of starlings are infected œ from this she proposed that Plagiorhynchus alters the behavior of the pill bug to make it more likely to beingested œ via controlled experiments she found that in fact this was the case, the pill bug‘s behavior was altered in several ways: œ Infected pill bugs spend less time in sheltered areas œ Spend more time in high humidity environments on light colored backgrounds 3 Exploitation: Predation, Herbivory, Parasitism & Disease 3 Exploitation: Predation, Herbivory, Parasitism & Disease 7 Exploitation: Predation, Herbivory, Parasitism & Disease • A Plant Pathogen that Mimics Flowers œ Observation: A Rocky Mt. Plant called Arabis exists for several years as a rosette then at some point bolts, producing flowers then seeds Found That: Arabis can be infected by a rust called Pucinia monoica which alters the life cycle of Arabis Upon infection the rust invades meristematictissue causing it to grow atypically the next year stem elongates leaves grow close together near the ends of the stem leaves take on a yellow color and resemble flowers of Rannunculus These yellow leaves attract many insects which in turn serve to spread the rust 8 Exploitation: Predation, Herbivory, Parasitism & Disease 7 Exploitation: Predation, Herbivory, Parasitism & Disease • The Entangling of Exploitation with Competition œ Predation, Parasitism, and Competition in Populations of Tribolium (flour beetle) œ last chapter observed competition between T. castaneum and T. confusum dictated by temperature and humidity œ it has also been observed that a parasite, Adelina, can effect this relationship 2 Exploitation: Predation, Herbivory, Parasitism & Disease • An Herbivorous Stream Insect and Its Algal Food œ in many cases the exploiter greatly effects the population it is exploiting œ Lamberti& Resh(1983) studied the larvae of a stream caddisfly, Helicopsyche • larvae forms a —portable house“ allowing it to feed upon algae and bacteria without being eaten itself • proposed that these larvae greatly effect the populations that it feeds upon because of this protection • reach densities of 4000 m2, this many individuals can greatly reduce their food supply 1 Exploitation: Predation, Herbivory, Parasitism & Disease œ Experimental Design #1 • Unglazed tiles (15.2 cm x 7.6 cm) placed on the bottom of a creek • Observed over a 7 week period œ Colonization by algae œ Invasion of Helicopsyche 10 Exploitation: Predation, Herbivory, Parasitism & Disease • Biomass of algae and numbers of the grazing caddisfly 11 Exploitation: Predation, Herbivory, Parasitism & Disease œ Experimental Design #2 • Placed control tiles directly on stream bottom • Placed experimental tiles 15 cm above the bottom, supported by a J œ rod that adults could not climb up and down to deposit eggs 12 Exploitation: Predation, Herbivory, Parasitism & Disease • Influence of elevating tiles on colonization by H. borealis 13 Exploitation: Predation, Herbivory, Parasitism & Disease • Influence of excluding H. borealis on abundance of bacteria and algae 14 Exploitation: Predation, Herbivory, Parasitism & Disease • An Introduced Cactus and Herbivorous Moth œ dramatic effects on populations can also occur in the absence of exploiters œ this is frequently the case with introduced species œ The cactus (Opuntia stricta) introduced into Australia during the mid- 1800‘s • By 1930 covered 24 million hectares • An attempt to control these cacti was the introduction of a mothlarvae, Cactoblastis œ Larvae had two adverse affects on the cacti » They fed on it directly » Created wounds that permitted the entrance of killing pathogens œ in 20 months the cactus population was reduced from 12,000/ha to 27/ha and a dynamic equilibrium was reached (as seen in nature) A similar attempt is being utilized to try and control purple loosestrife and wooly adelgids 15 Exploitation: Predation, Herbivory, Parasitism & Disease 16 Exploitation: Predation, Herbivory, Parasitism & Disease • A Pathogenic Parasite, a Predator and its Prey œ many ecological experiments are done at a small scale and interpolated up, on a few rare instances we have the ability to observe large scale, natural events œ Sweden, Lindstrom (1994) œ discussed the relationship between a mite that caused mange in fox and the effect their decline had on hare populations 17 Exploitation: Predation, Herbivory, Parasitism & Disease 18 Exploitation: Predation, Herbivory, Parasitism & Disease • Cycles of Abundance in Snowshoe Hare and Their Predators œ in many populations cycles of —boom and bust“ are observed, these can take place on a days to decades scale œ a classic study is one where data accumulated from the Hudson Bay Co. over a 200 yr. Period was used 19 Exploitation: Predation, Herbivory, Parasitism & Disease 20 Exploitation: Predation, Herbivory, Parasitism & Disease œ Several explanations for these observations have been proposed: • Elton (1924) œ variations were tied to sun spots œ MacLulichand Moran shot this down since they did not correspond • Keith (1963) œ came up with —overpopulation theories“ œ he stated that as the population grew: œ Disease and parasitism increased œ High densities resulted in physiological stress œ Starvation resulted as food supply decreased With further studies Keith found that food supplies and predators have a great affect 21 Exploitation: Predation, Herbivory, Parasitism & Disease Food Supply Hare require a great deal of food, during winter eat as much as 1500 g/day (typically 300 g/day) œ during this time biomass has decreased from 530 kg/ha in late November to 160 kg/ha by late March, frequently resulting in food shortages Hare also affect their food œ heavy browsing causes them to produce turpenes and phenolicresins, hare find these substances distasteful œ the affects of this can last for up to 2 years œ some feel that this —triggers“ the 10 year cycle Predators Many other predators feed upon snowshoe hare: Goshawks, Great Horned Owls, Red Fox and Coyotes 22 Exploitation: Predation, Herbivory, Parasitism & Disease • Experimental Tests of Food and Predations Impacts œ Performed detailed, long term experiments with snowshoe hares inan attempt to answer the question • 8 years • 1 km2 blocks in undisturbed boreal forest; separated by 1 km • 3 controls, 6 experimental • Hares given unlimited food on 2 experimental blocks • 2 of the plots were well fertilized, increasing food quality • Fenced in 2 plots, excluding mammalian predators but not birds, one received supplemental food (these were not replicated because ofintense demands of checking the fences, temps of -45o C 23 Exploitation: Predation, Herbivory, Parasitism & Disease œ Results • Hares increased in all plots, followed by a decline • Fertilizer did increase plant growth but not number of hares • Hare numbers did increase, compared to controls on plots that: œ Supplemented food (3x hare increase) œ Predator reduction (2x hare increase) œ Predator reduction + food supplementation (11x hare increase) 24 Exploitation: Predation, Herbivory, Parasitism & Disease • Population Cycles in Mathematical and Laboratory Models œ Mathematical Models œ Lotaka/Volteraœ Volteraobserved that during WWI, when fishing was reduced, the number of sharks increased while their prey decreased œ from this these two attempted to develop a model to reflect these trends œ in their model two major assumptions are required • Host population increases exponentially • Size of the population is limited by an exploiter 25 Exploitation: Predation, Herbivory, Parasitism & Disease 26 Exploitation: Predation, Herbivory, Parasitism & Disease Graphically these equations show a typical pattern showing reciprocal effects 27 Exploitation: Predation, Herbivory, Parasitism & Disease œ Laboratory Models œ Utida(1957) set up an experiment using the Adzuki Bean Weevil and a parasitoid wasp œ these were grown in petridishes at 30o C and 75% RH 28 Exploitation: Predation, Herbivory, Parasitism & Disease • Refuges and Host Persistence in Laboratory and Mathematical Models œ Gause‘s Experiments 29 Exploitation: Predation, Herbivory, Parasitism & Disease œ Huffaker(1958)