Chp 9 - Predation and Herbivory_90fc32c.pdf

BIOL207 General Ecology Species Interactions - Predation and Herbivory Modes of interactions - Basic definitions Evolution of defenses in animals Evolution of defenses in Plants Counter adaptations in consumers Importance of consumption on ecosyste...

BIOL207 General Ecology Species Interactions - Predation and Herbivory Modes of interactions - Basic definitions Evolution of defenses in animals Evolution of defenses in Plants Counter adaptations in consumers Importance of consumption on ecosystems  Species Interactions Examples BIOL207 - General Ecology Species Interactions 3 Example – 1 : Myxoma virus – vs – Rabbits Introduced rabbits became a pest in Australia (1859) Resulting in agricultural problems Counter measures Poisons Predators Solution = Myxoma virus Used in 1950 Isolated from the infected rabbits of South America Transmitted by mosquitoes Results of the myxoma epidemics 1st outbreak = 99.8% of infected rabbits died 2nd outbreak = 90% of infected rabbits died 3rd outbreak = 40% - 60% of infected rabbits died BIOL207 - General Ecology Species Interactions 4 Example – 1 : Myxoma virus – vs – Rabbits Evolutionary responses in the rabbit and the virus The rabbit: Genetic factors conferred resistance to the disease They existed in the rabbit before Myxoma exerted selective pressure for resistance Most of the surviving rabbits were resistant The virus population: Less virulent strains of the virus became more prevalent Mosquitoes bite only living rabbits Surviving virus strains didn’t kill their host They were readily dispersed to new hosts by mosquitoes BIOL207 - General Ecology Species Interactions 5 Example – 2 : Prickly pear cactus – vs – cactus moth The prickly pear cactus is native to North and South America In the 19th century – cactus species were introduced to Australia They were used as ornamental plants and living fences for pastures They grew rapidly and became a pest in the Australian pastures and rangelands In 1920s – Biologists fought the cactus spread Cactus moths (cactus herbivores) were collected from S. America and introduced to AUS The caterpillar life-stage of the moth consumes proportions of the cactus plants The injuries caused to the plant allow pathogen to infect the plants BIOL207 - General Ecology  Species Interactions Modes of interactions - Basic definitions BIOL207 - General Ecology Species Interactions 7 Modes of species interactions Consumer resource Herbivore-Plant Predator-Prey Parasite-Host Competition Mutualism Commensalism Amensalism BIOL207 - General Ecology Species Interactions 8 Basic definitions Herbivore: organisms that exclusively feed on plant tissues They eat whole plants or parts of a plant May act as predators (eating whole plants) or parasites (parts of a plant) Grazers eat grasses and herbaceous vegetation Browsers eat woody vegetation Predator: a consumer that kills its resource – removing it from the resource population Mesopredators Examples: coyotes, weasels, feral cats, etc. They are small carnivores that consume herbivores Top predators Examples: wolves, mountain lions, sharks They consume mesopredators and herbivores Parasite: an organism that consumes part of their resource without killing it Parasitoid: an organism that consumes part of their resource leading to its death Detritivore: An organism that feeds on dead organic matter No impacts on the species producing the resource in this case BIOL207 - General Ecology  Species Interactions Evolution of defenses in animals BIOL207 - General Ecology Species Interactions 10 Evolution of defenses in animal species Defenses against predators To understand the strategy of prey defense we need to understand the predator mode of hunting Active hunting They spend most of their time moving around searching for prey Ambush hunting (or sit-and-wait hunting) They spend most of their time waiting for the prey to pass by Prey responds to predator hunting strategy by evolving defenses Behavioral defenses Crypsis Structural defenses Chemical defenses Mimicry BIOL207 - General Ecology Species Interactions 11 Evolution of defenses in animal species Behavioral defenses Examples: Alarm calling Used by many species of birds and mammals They warn their relatives when a predator is approaching Spatial avoidance The prey in this case moves away from the predator If the predator moves towards them – they continue to move away Reduction of activity The prey tries to avoid the contact with the predator They reduce their movements to minimize the chance of encounter with a predator Experiment – Tadpole species behavior with dragonflies A total of 6 different species of tadpoles was used The tadpoles were put in aquaria with a cage inside Each species activity was assessed with and without a predator in the cage Empty cages were used to set the control for this experiment BIOL207 - General Ecology Species Interactions 12 Evolution of defenses in animal species Behavioral defenses Experiment – Tadpole species behavior with dragonflies When the predator was absent each species had different activity level All tadpole species reduced their activities in the presence of the predator BIOL207 - General Ecology Species Interactions 13 Evolution of defenses in animal species Crypsis It is a second adaptation strategy to protect against predators The prey adapts its appearance to resemble to inedible objects (not concealed) It is based on camouflage that match the environment Or a camouflage that breaks up the outline of an individual to blend with the background Examples: species that resemble to sticks, leaves, flower parts, bird droppings, etc. BIOL207 - General Ecology Species Interactions 14 Evolution of defenses in animal species Crypsis Some species develop a fixed color pattern that aids in Crypsis Other species are able to rapidly change color in ways to match the background (octopus, chameleon) BIOL207 - General Ecology Species Interactions 15 Evolution of defenses in animal species Structural defenses Some species employ mechanical defenses This reduces the predator ability to capture the prey Also reduces the attack efficiency and handling of the prey Examples Permanent adaptations (non-plastic phenotype) Porcupine covered with > 30,000 flesh penetrating quills Some defenses are activated only when in danger (plastic phenotype) Water fleas Tiny crustaceans that detects chemical cues of predators early in their life They develop spines over their body which become permanent Other fleas without the chemical cues do not develop spines BIOL207 - General Ecology Species Interactions 16 Evolution of defenses in animal species Structural defenses Examples Changes in the overall shape of the body The Crucian Carp Habitat: EU and Asia Develops a deep, hump-shaped body when smelling a predator This morph has a greater muscle mass It can accelerate quickly to run away from predators BIOL207 - General Ecology Species Interactions 17 Evolution of defenses in animal species Chemical defenses Skunks spray potential threats with foul-smelling chemicals Monarch butterfly caterpillars Feed on milkweed Store milkweed toxins The adult butterfly becomes distasteful Bombardier beetle Have glands in their abdomen Each gland secretes a distinct chemical When threatened the beetle mixes the chemicals Ejects the mixture which is about 100˚C Some prey highlight their toxins to the predators through warning coloration This is called “aposematism” which is the development of “aposematic coloration” Predators quickly learn to avoid markings of high contrast colors (yellow, blue, black, red, orange, etc.) These colors are the most used ones in nature to highlight toxic organisms BIOL207 - General Ecology Species Interactions 18 Evolution of defenses in animal species Chemical defenses Examples on Aposematism Some predators learn by ingesting a toxic prey – if they survive, they will avoid it Some predators evolved innate aversion to brightly colored species – they do not need to try and learn! BIOL207 - General Ecology Species Interactions 19 Evolution of defenses in animal species Chemical defenses Chemical defenses are costly It requires large investments of energy and nutrients Many species rarely develop high energy demanding toxic glands Some species accumulate toxins from food (like some plants) – they need energy to avoid self intoxication Solution = MIMICRY Mimicry It is adopted by edible species which resemble to inedible toxic species The “mimic” is the edible species The toxic species is the “model” The mimic benefit from the learning behavior of predator that avoids inedible models BIOL207 - General Ecology Species Interactions 20 Evolution of defenses Mimicry There are 2 types of mimicry Batesian Mimicry Named after Henry Bates The model is toxic in this case The mimic is non-toxic (b) and (c) : hover fly and hornet mimic of the toxic wasp (a) BIOL207 - General Ecology Species Interactions 21 Evolution of defenses Mimicry Müllerian Mimicry Named after Fritz Müller The mimic is toxic and the model is more toxic The mimicry complex can include several populations of inedible species resembling one another BIOL207 - General Ecology  Species Interactions Evolution of defenses in Plants BIOL207 - General Ecology Species Interactions 23 Evolution of defenses in plants Plant adaptations to fight herbivory Low nutritional content of plant tissues Fruits and seeds = high nutritional values Young leaves = low indigestible cellulose Some plants produce secondary compounds “tannins” which can bound to proteins and limit their digestibility Structural defenses Spines and hairs (a) Cholla Cactus (b) Prickly Pear cactus Tough seed coats Sticky gums and resins Toxic compounds synthesized by the plants They are energy and resources expensive Plants can develop constitutive –or– induced toxin production BIOL207 - General Ecology Species Interactions 24 Evolution of defenses in plants Plant chemical defenses Constitutive defense Toxins are high all the time in the organism It is costly in terms of energy and resources Induced defense – toxins produced occasionally Before any threat Low energy required because no toxins are elaborated After initial herbivory Higher energy is required because of toxin elaboration Example: herbivory mites Growing on: Control plants (no previous herbivory – no toxins) Exposed plants (with initial herbivory – toxins elaborated) Adult mites and eggs numbers High on control plants Reduced on exposed plants BIOL207 - General Ecology  Species Interactions Counter adaptations in consumers BIOL207 - General Ecology Species Interactions 26 Counter adaptations in consumers Consumers have adaptations for exploiting their prey Some whales are filter feeders Spiders make webs to subdue prey Large cats have adaptations to capture fast prey Size difference between consumer and resource can be a problem If a prey species is too small – it may be too hard to handle If a prey species is too large – the predator may not be able to subdue it Counter adaptations example - Blue whales They eat tiny shrimps They rely on filters in their oral cavity Some adaptations take practice (parental investment) Cubs of almost every predator need field training to discover their potential Cheetahs are fast runners Jaguars are excellent stalkers and tree climbers BIOL207 - General Ecology Species Interactions 27 Counter adaptations in consumers Variations in consumers’ digestive systems The form and the function of predator digestive system reflects the diet Vertebrate teeth are adapted to dietary items Herbivores No canines Numerous cubic shaped premolars Numerous cubic shaped molars Carnivores Incisors to cut the skin Knifelike premolars to scrap the meat Few molars BIOL207 - General Ecology Species Interactions 28 Counter adaptations in consumers Variations in consumers’ digestive systems Vertebrate digestive system Herbivore features Elongated digestive tracts Fermentation chambers Digest long fibrous molecules Stomach may elaborate dispersive enzymes to enhance digestion of leaves Carnivores features: Smaller stomach Small intestine Small hindgut BIOL207 - General Ecology Species Interactions 29 Counter adaptations in consumers Variations between similar species (ex: herbivores) Horses Upper incisors for cutting fibrous stems Flat-surfaces molars for grinding Deer Lack upper incisors They grasp and tear vegetation Molars are used for grinding Carnivores Developed canines to grab prey Knifelike premolars BIOL207 - General Ecology Species Interactions 30 Counter adaptations in consumers More variations – distensible jaws in snakes Shifting articulation from vertical to horizontal The quadrat bone articulation becomes fixed The supratemporal articulation becomes mobile BIOL207 - General Ecology  Species Interactions Importance of consumption on ecosystems BIOL207 - General Ecology Species Interactions 32 Importance of consumption on ecosystems Effects of herbivory on vegetation and ecosystems Benefits of herbivory Natural role – Grassland example Herbivores can consume 30 to 60% of aboveground vegetation in grasslands This reduces the dominance of grass and allow other species to grow Pest control Prickly pear cactus in Australia – controlled by the introduction of a moth Klamath weed in California – controlled by the introduction of a beetle Costs of herbivory – occasional outbreaks Outbreaks of tent caterpillars (like gypsy moths) excessively consumes leaves Sometimes the outbreak leads to a complete defoliation of forest trees BIOL207 - General Ecology Species Interactions 33 Importance of consumption on ecosystems Effects of herbivory on vegetation and ecosystems Herbivory impacts can extend to species competition and ecosystem stability Example: role of voles in the ecosystem Voles feed on some plants (food plants) Food plants are in competition with other species (others) An experiment was designed: Patch without exclosure (with voles) Patch with exclosure (voles excluded) Results With voles Food plants reduced Other plants grew well Voles excluded Food plants boomed Other plants reduced Conclusion: Food plants are strong competitors Other plants are weak competitors Voles reduce food plants and allow others to develop BIOL207 - General Ecology  END BIOL207 - General Ecology