Introduction • _________________: Interaction between populations that enhances fitness of one individual while reducing fitness of the exploited individual. • ___________ is an insect larva that consumes the host.
Parasites That Alter Host Behavior • Spring-Headed Worm (Acanthocephalans) changes behavior of amphipods in ways that make it more likely … • Infected amphipods swim toward light, which is usually indicative of shallow water, and thus …
Parasites That Alter Host Behavior • Rust fungus Puccinia monoica manipulates growth of host mustard plants (Arabis spp.). • Puccinia infects Arabis rosettes and invades actively dividing ________________________. • Rosettes rapidly elongate and become topped by a cluster of bright yellow leaves. • Pseudo-flowers are fungal structures including sugar-containing spermatial fluids. • Attract pollenators
Entangling Exploitation with Competition • Park found the presence/absence of a protozoan parasite (Adeline tribolii) influences competition in flour beetles (Tribolium). • Adelina lives as an intercellular parasite. • Reduces density of T. castaneum but has little effect on T. confusum. • T. castaneum is usually the strongest competitor, but with the presence of Adelina, T. confusum becomes strongest competitor.
Exploitation and Abundance • Introduced Cactus and Herbivorous Moth • Mid 1800’s:prickly pear cactus Opuntia stricta was introduced to Australia. • Established populations in the wild. • Government asked for assistance in control. • Moth Cactoblastis cactorum found to be effective predator. • Reduced by 3 orders of magnitude in 2 years.
Cycles of Abundance in Snowshoe Hares and Their Predators • Snowshoe Hares (Lepus americanus) and Lynx (Lynx canadensis). • Extensive trapping records. • Elton proposed abundance cycles driven by variation in solar radiation. • Keith suggested overpopulation theories: • Decimation by … • ____________________________ at high density. • _____________ due to reduced food.
Snowshoe Hares - Role of Food Supply • Live in boreal forests dominated by conifers. • Dense growth of understory shrubs. • In winter, browse on buds and stems of shrubs and saplings such as aspen and spruce. • One population reduced food biomass from 530 kg/ha in late Nov. to 160 kg/ha in late March. • Shoots produced after heavy browsing can increase levels of plant chemical defenses. • Reducing usable food supplies.
Snowshoe Hares - Role of Predators • Lynx (Classic specialist predator) • Coyotes may also play a large role. • _______________ can account for 60-98% of mortality during peak densities. • Complementary: • Hare populations increase, causing food supplies to decrease. Starvation and weight loss may lead to increased predation, all of which decrease hare populations.
Population Cycles in Mathematical and Laboratory Models • Lotka Volterra assumes host population grows exponentially, and population size is limited by parasites, pathogens, and predators: dNh/dt = rhNh – pNhNp • rhNh = Exponential growth by host population. • Opposed by: • P = • Nh = • Np =
Model Behavior • Host exponential growth often opposed by _________________. • Host reproduction immediately translated into … • Increased predation = • More predators = • Larger predator population eventually reduces host population, in turn reducing …
Refuges • To persist in the face of exploitation, hosts and prey need … • Gause attempted to produce population cycles with P. caudatum and Didinium nasutum. • Didinium quickly consumed all Paramecium and went extinct. (Both populations extinct) • Added sediment for Paramecium refuge. • Few Paramecium survived after Didinium extinction.
Predator Satiation by Periodical Cicadas • Periodical cicadas Magicicada spp. emerge as adults every 13-17 years. • Densities can approach 4x106 ind / ha. • Williams estimated 1,063,000 cicadas emerged from 16 ha study site. • 50% emerged during four consecutive nights. • Losses to birds was only 15% of production.
Protection in Numbers • Predator’s response to increased prey density: Prey consumed x Predators = Prey Consumed • Wide variety of organisms employ … • Prey can reduce…
Size As A Refuge • If large individuals are ignored by predators, then .... • Peckarsky observed mayflies (Family Ephenerellidae) making themselves look larger in the face of foraging stoneflies. • In terms of optimal foraging theory…