Wildlife Eco and Mgmt Notes 4
Wildlife Eco and Mgmt Notes 4 390
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This 12 page Class Notes was uploaded by Jacob Erle on Wednesday September 30, 2015. The Class Notes belongs to 390 at Syracuse University taught by Dr. Sharron Farrell in Fall 2015. Since its upload, it has received 27 views. For similar materials see Wildlife Ecology and Management in Foreign Language at Syracuse University.
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Date Created: 09/30/15
Wildlife Ecology and Management Notes, Week 4 9/22/15 Populations and Predation -focus on trophic interactions Predation – consumption of resources from another organism -historically, emphasis was on effects of predators on prey Predator control/eradication, regardless of consequences Trophic interactions -trophic control and trophic cascades -Predator-prey dynamics -see hare-lynx cycles (Hewitt 1921, Elton 1924) -Release of Mesopredators – relatively small carnivores that consume autotrophs (producers) -Top predators – consume both producers and other consumers (i.e. mesopredators) -Removal of sea otters, wolves in Yellowstone can have a cascade effect on rest of ecosystem -increasing awareness of importance of predators Experiment to test bottom-up regulation – was it availability of food to rabbits? -supplemental food raised carrying capacity but still showed cycle Experiment to test top-down regulation – exclusion of lynx from certain areas -higher density of predators => lower hare reproduction; combined with direct mortality from predators justifies this response Lotka-Volterrra model (1920s) – uses predator-prey interacts as a base model to examine potentially similar effects seen in other populations (very simple model) Makes several simplifying assumptions: 1.)Prey population grows exponentially in absence of predators 2.) predator population will starve in absence of prey pop 3.) predators can consume infinite quantities of prey 4.)No environmental complexity (both populations are moving randomly through a homogeneous environment). Prey population in absence of predators Where N = number of prey r= prey growth rate -Describes rate of change of prey population (N) with respect to time (t) Composed of difference between prey birth rate and prey mortality rate OR Where α = attack rate N = population of prey P = population of predators Predator population without prey ∆ P =−qP ∆t Predator population with prey OR Where P = number of predators B = predator birth rate q = predator mortality rate c = conversion rate – ability of predator to convert food into viable offspring -cαPN means increases in the predator population are proportional to predator X prey abundance -As P and N increase, their encounters are more frequent, but the actual rate of consumption depends on attack rate -Improved understading and new viewpoint on predator role -more efforts needed to explore needs of predators, how prey affects predators -Energetics -Predators types: specialists vs. generalists -Foraging behavior L-V model -simple enough to be mathematically manageable and useful and complex enough to represent a system realistically -Caveat reliance on unrealistic assumptions -Prey populations are limited by food resources and not just by predation -No predator can consume infinite quantities of prey. -Better fit by models that incorporate terms representing carrying capacity for the prey population, realistic functional responses (how a predator's consumption rate changes as prey densities change) for the predator population, and complexity in the environment. Strenseth et al 1997 -The plant species in hare diet appears compensatory to each other -The predator species may be seen as an internally compensatory factor. -The lynx populations are regulated from below through prey availability. Classic view of an equal hare–lynx interaction is too simplistic; the classic food chain structure is inappropriate -the hare is influenced by many predators other than lynx -the lynx is primarily influenced by snowshoe hare. Food Habits Prey Selection -Generalists vs. Specialists -can be studied by stomach or scat analysis – can be invasive, difficult to discern -Observation of actual predation events – can be tough to collect Finding and Capturing Food Predator’s functional response - rate of prey capture as function of prey abundance Type I – linear increasemore dense prey = higher consumption until reaching a max rate -slope = consumer’s attack rate -possible only when handling time = 0 & predators don’t get fullnot realistic Type II – rate of consumption rises with prey density but eventually levels off (asymptote) and all available time is spent handling prey; consumption rate stays constant regardless of increases in prey density - handling time, rather than prey availability, limits the number of prey items that a predator can consume -handling time for every prey isn’t associated with prey density; at low prey densities, a smaller proportion of predator’s time is spent handling prey, even if the predator attacks every prey item available -no learning involved Type III – similar to Type II EXCEPT at high prey density saturation occurs -incorporates potential for prey switching, learning time involved, or both -Learning time - improvement of predator’s searching and killing effectiveness as prey density increases Foraging – searching for food and obtaining resources, all about TRADE- OFFS Optimal Foraging Theory (1966) – meant to describe foraging for an individual -understand predator-prey relationships; can be helpful with habitat management -successful foraging essential to survival; strategic, not random -use decision theory to predict foraging behavior Optimal Model - Forager encounters different prey types & must choose which prey to attack -Prey items have differing profitability, dependent on -time to find prey -time & energy to capture -time and energy for handling and eating -energy prey provides Ultimately, animals choose foraging criteria for maximizing fitness. They should ignore low profit prey when more profitable ones are sufficiently available. -Trade-off between intake rate & switching, searching for other prey Patch Selection Theory – prey is patchily distributed -see apple picking -depends on how much time individual spends on one patch before moving on to next one (amount of travel time) -if travel time increases, optimal time to stay in a patch also increases -prey availability in patch drops due to predator’s foraging activity -depletion of prey -evasive actions by prey -to maximize net gain of resource(s) predators should leave at the point (max net gain) that gives greatest gain or food intake per unit of time Assumptions 1.)Each patch type is recognized instantaneously 2.)Travel time between patches is known by the predator 3.)Gain curve is smooth, continuous, & decelerating 4.)Travel time between & searching within a patch have equal energy costs Central Place Foraging Theory – variation of patch model -describes the behavior of a forager that must return to a particular place to consume food, to hoard food or feed it to a mate/offspring. Group Foraging – animals find and eat prey as a group -can occur when: -foraging in a group is beneficial -when groups of individuals simply forage in the same space Costs and Benefits -Group vigilance many eyes reduces risk of predation -Dilution –reduced predation risk (safety in numbers) -enhanced foraging success -capture larger prey -variety of prey or funnel prey making them easier to capture -Competition for available resources by conspecifics Energy Requirements Metabolism -basal metabolic rate, BMR (seen in many birds and vertebrates) -often higher for smaller animals To estimate BMR for placental mammals = 293 × kg 0.75 kj/day Activity -Daily actions: locomotion, grooming, preening, foraging, evading predators, etc. -Assessed by – ethnograms, activity/energy budgets -sampling across 24hr day (in increments) is helpful -very intensive studying process, not a lot to of in-depth studies found for this Thermoregulation -fairly minor expenditures -short term = feathers/ fur undergoes piloerection, shiver, sweat -long term = winter coat, fat deposits, torpor/hibernation Production & Reproduction -Somatic growth – building bones, muscle, connective tissue, fur, feather -Reproductive demands – often higher for females, varies over time (over the course of 1 reproductive year/season) 9/24/15 Behavioral Interactions -Competition, intra (conspecifics) vs. interspecific (members of different species)? Intraspecific Interspecific food food space space mates -competition is antagonistic interaction -density dependence is generally negative (as density increases, fitness decreases) How prevalent is competition? Interspecific -leads to radiation of species (niche partitioning) -see warbler/finch feeding habits Intraspecific Scramble competition – each individual wants a piece of that resource (food, elbow room) Interference Competition – presence of competitors excludes use of resources by others Competition for space & resources in space – Ideal free distribution (Fretwell, 1972) -predicts animals will make decisions about where to go based on quality of patches available -Will choose most profitable patch -depends on patch’s starting quality and how many others are using resource -group of organisms will distribute among patches equally/proportionally -in patches of equal value, the same # -individuals will hit the most valuable patches first, and then move onto next most suitable patch Assumptions -Food resources only – each patch has unique quality determined by available resources -Perfect perception and complete information – individuals can measure patch quality based on available resources -Instant decision – individuals are aware of patch value, allowing them to choose the ideal patch -Zero-sum game – increase # of individuals in a patch reduces patch quality via competition -Democracy – ability to move to highest quality patches, and all individuals have same competitive abilities Unequal Competitors – IFD addressed using weights to show differences in abilities Ideal Despotic Distribution – formalize idea of multiple competitive abilities -differs depending on how organisms use space -nomadic doesn’t involve much interference competition -home ranges overlap with other, could involve scramble competition Competition, territoriality and resource defense is it worth it? -what do you spend energy defending (cost and benefit to protecting resource(s)) Male Barrow’s Goldeneyes -defend their turf in open water, invisible lines on water surface -territories not touching shore are smaller, less defendable and more energetically and usually left early -shoreline leaves you with a clear boundary to check and defend Economic defendability -defense restricts access to resources, different systems vary in amount of restriction -benefit = increase in available resources -cost = takes energy and time to protect -territory must ultimately yield net benefits greater that if using area non- territorially -defense is more likely when animals con control resource accessibility, and/ or if use of resource reduces density of resource Renewal rate and spatiotemporal patterns of resource: -high depletion rate low renewal rate = fruit trees (not good sense to defend) -high depletion rate high renewal rate = more likely (termite mounds, ant hills) -resources unpredictable in space and time = unlikely to defend -resource predictable in time and space = more likely to defend *Remember - all related to negative density dependence and resources are limiting, which isn’t always the case Dispersal (Emigration) -driven in part by resource availability -Natal dispersal – juvenile moves from birth site to new location -Breeding dispersal – adults move between breeding attempts -Effective dispersal – when either mode of dispersal ultimately results in successful breeding attempt (spreading out of genetic lineage) -can vary by type, species, motive and distance Why Disperse? -response to environmental factors: resource availability, competition (density dependence), parental/kin aggression Ex. Columbian ground squirrels, Spanish Imperial Eagles, Red foxes -Innate dispersal – genetic tendency to disperse, sometimes dependent on specific env conditions in time and space Ex. Belding’s ground squirrels Positive intraspecific interactions -Group foraging -group vigilance -dilution effect -increased foraging success = more eyes looking for good food spots -Cooperative defense – alarm system, confusion and/or mobbing behaviors -Facilitation – presence of an individual can increase benefits for other species for habitat -Mating and reproduction Negative density dependence: -antagonistic interactions, competitive exclusion, avoidance, fighting, separation Positive density dependence (+ correlation between density and fitness) Allee effect -attraction (hanging with the big boys now) -see lekking, clustering Important to conservation - habitat available for colonials, reproductive capabilities (mating opportunity) END OF NOTES
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