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WEEK ONE Ecology - The study of interactions that determine the distribution and abundance of organisms (among members of the same species, individuals of 2 or more species or among individuals and their physical environment) Ecosystem - A group of interacting organisms and t...

WEEK ONE Ecology - The study of interactions that determine the distribution and abundance of organisms (among members of the same species, individuals of 2 or more species or among individuals and their physical environment) Ecosystem - A group of interacting organisms and their physical environment The first ecologists were called… - Naturalists 4 approaches to ecology - Observation and natural history - Experimental ecology and null hypothesis testing - Multiple hypothesis testing with best-fit comparisons - Ecological modeling Observation and natural history - Carefully watching nature and natural phenomena and constructing narrative explanations Focal factor - The key aspect of an ecological system that is being altered/manipulated to see how the changes affect ecological outcomes and responses - The manipulated aspects are treatments Extraneous factor - Nonfocal elements Hypothesis testing 1. Make observations about the natural world and raise questions 2. Propose the idea as a null hypothesis (focal factor does NOT have an effect) and an alternative hypothesis (focal factor DOES have an effect) 3. Conduct the experiment and collect data to determine which hypothesis is supported Advantages of experimental and hypothesis testing - Researchers consider observations to create specific falsifiable hypotheses - Encourages scientists to identify critical factors relevant to the hypothesis - Manipulation of factors demonstrates focal factors and removes from influence of extraneous factors Multiple hypothesis approach - Shift from falsifying a hypothesis suggesting a particular effect has no effect to evaluating which of several reasonable hypotheses are most likely to be true (best-fit hypothesis) Conceptual vs. mathematical vs. analytical vs. simulation - Conceptual: theoretical; various components in relation to each other, a formalized idea about how things work (e.g. different factors affecting population growth of a  plant); used to frame and analyze a set of questions about how an ecological system performs under various conditions - Mathematical: conceptual model formalized into a mathematical model; set “in motion” to explore how the system responds when one or more variables change (e.g. change in population size) - Analytical: those models are analytical since the equations can be solved or produce important insights by analyzing the relationships among variables - Simulation: version of conceptual/mathematical that is run on a computer to predict the model’s performance; uses a series of functions to connect different components of a system; the goal is to alter one or more components and track how other components of the ecosystem respond Early vs. modern ecology - Early: natural history through observation and construct narrative explanations, taxonomy (classifying organisms) - Modern: science is a collection of knowledge based on empirical evidence and measurable factors; testability and falsifiability; science has limits and focuses on developing a mechanistic understanding Developing a mechanistic understanding - Hypothesis testing through manipulative experiments, multiple hypothesis testing, ecological modelling Observations - First step in scientific method; formulated as patterns or phenomena; used to generate research questions Hypothesis vs. prediction - Hypothesis: proposed, testable explanation often answering a research question; possible general explanation of cause and effect; explains a pattern and contains a mechanism (because); present tense and leads to a prediction - Prediction: statement of expected outcome is hypothesis is correct; forecasts outcome of experiment or study; in the future tense (will) Benefits and limitations of experiments - When properly designed, they control for extraneous factors, ensure results are due to the variable being tested, provide reliable and replicable data; establish a clear cause-and-effect relationship between manipulated variables and observed outcomes - Lack of real-world complexity, imposes limits on type of organism and scale of study, ethical constraints Experiments vs. observational studies - Observational: monitor and record data as they occur naturally without manipulation; more accurate reflection of real-world conditions, avoid ethical issues and data can be collected over vast spatial and temporal scales Ecological detective - Evaluating multiple hypotheses simultaneously, typically observational - Present competing hypotheses and conclusions based on strength of evidence, used in large-scale studies with multiple causative factors Ecological modelling - Provides a way of exploring how various factors affect ecological dynamics without manipulating real ecosystems; used in theory using mathematical or computational simulations - 2 general types: conceptual and mathematical - Helps ecologists understand complex systems, test hypotheses and forecast change Emergent property - A property that is not present in the level’s component parts but emerges from these parts’ interactions and relationships - Arise from the interactions and relationships among the components at each level of biological organization - E.g. nutrient cycling (is facilitated by the interactions between organisms) Feedback and synergy - Feedback: a process where the output or outcome of an ecological system or interaction influences the system’s subsequent behaviour or functioning, either amplifying (positive feedback) or dampening (negative feedback) the original process - Synergy: the interaction between 2 or more components of an ecosystem that results in a combined effect greater than the sum of their individual effects (e.g. 2+2 = 1000) Describe how a system changes - Inputs > outputs = growth - Outputs > inputs = decline - Inputs = outputs = equilibrium Quantitative reasoning - Involves applying math to this measured/counted information to produce a deeper understanding of the topic Data literacy - Ability to collect, analyze, make sense of and communicate the meaning of qualitative and quantitative data Building a conceptual model 1. Become familiar with the question/problem 2. Identify specific aspects most important to include; identifying key elements that produce the effect that the model will explore 3. Drawing - a box that represents the one factor determined to be most critical to track through time; think about how it is filled or emptied (arrows for births/deaths); inflow and outflow (birth and death rates) Mathematical model vs. deterministic model vs. stochastic model - Mathematical: include mathematical representations for parts of all of the model - Equations represent elements, have variables (vary) and parameters (constant) - Deterministic: the outcome is determined by input parameters and initial conditions (no randomness or variability) - Stochastic: elements of randomness or uncertainty (outcomes vary) Characterize different types of data - Categorical: no inherent numerical values, presented as categories that may be ordered or nominal (colour, sex, status) - Categorical data that have a natural order are ordinal categorical variables (e.g. life stage, size) - Numerical: inherent numerical values associated - Continuous numerical variables: come from measurements; can take any value - Discrete: only come in whole numbers Visualizing independent and dependent variables - Dependent on the y-axis, independent on the x-axis - Continuous independent -> scatterplot - Categorical independent -> boxplot WEEK TWO Climate vs. weather - Climate: an expected pattern in the physical factors that make up the world (e.g. precipitation, heat, humidity); it defines biomes, influences species distributions, impacts ecological processes and regulates nutrient/water cycles - Weather: observed day-to-day variation in physical factors at a specific time and place; harder to predict Niche - Range of conditions that a species must be able to tolerate and still be able to survive and reproduce; range of abiotic and biotic conditions that an organism can tolerate Main ideas of solar radiation - Drives atmospheric and oceanic circulation - Influences patterns of weather and precipitation - More intense at the equator than at the poles Main ideas of atmospheric circulation - The large-scale movement of air and the mechanisms that create differences in air temperatures across Earth - Cold air weighs more than hot air (hot air rises, cold air sinks) - Atmospheric pressure decreases as you go up in elevation - Compressed air heats up, expanding air cools down - Warm air holds more water than cold air - High solar radiation at the equator leads to rainfall all year; vegetation thrives in warm and moist conditions - The cycle of warming, rising and cooling air creates low atmospheric pressure, leading to a rising air column Hadley cells - From the equator, cold, dry air descends as it moves north/south which produces areas of high pressure -> the air warms up and reaches the surface where it is warm and dry (deserts, tropical rainforests) Ferrel cells - The airmass circulating between latitudes of 30° and 60° north and south - The dry, warm air from the desert moves away from the equator and another band of low pressure forms; the air rises leading to expansion and cooling forming condensation and rain Polar cells - Produce another high pressure area at each polar region; the high pressure is due to cold, dry air returning to the surface Greenhouse effect - Heating and cooling of air creating atmospheric circulation cells, driving precipitation Coriolis effect - Daily rotation of the Earth causing circulation patterns - The deflection of air and wind patterns in bands around the globe caused by Earth’s daily rotation on its axis; causes air masses moving north or south over the surface of Earth to be deflected east or west - Air moving away from equator moves east; air moving towards equator moves west - Northern hemisphere oceanic water move clockwise; Southern hemisphere oceanic water move counter-clockwise Rain shadows - High-elevation mountains block air circulation causing climatic patterns called rain shadows (causes air masses to lose/deposit moisture on the front/windward side while air rises and cools forming rain clouds and create dry conditions on the back/leeward side - rain shadow forming a desert) Heat capacity and continental effect - Heat capacity: how much energy has to be added to a substance to raise temperature by 1°C - Continental effect: difference between centers of continents and coasts (big temperature swing in centre of continents but buffered on the coasts) Terrestrial biome descriptions - Usually described by characteristics of the dominant plant community (factors affecting primary productivity - synthesizing organic material through photosynthesis) Climate diagram - A graph that depicts 2 aspects of a region’s climate: temperature and precipitation as 2 independent y-axes - Orange line: average monthly temperature; blue: average monthly precipitation - Blue shading indicates precipitation levels likely sufficient for growth; yellow shading indicates dry conditions when evaporation outpaces precipitation Ecozone - Areas of Earth with distinct environmental conditions - Dependent on temperature, precipitation, topography, geological factors, soil, disturbance events, human influences Features differentiating terrestrial biomes - How well soil holds water dictated by depth, composition, texture and amount of organic material in soil Tropical rainforest - At or near equator - Temperature uniformly warm year-round; typically don’t experience seasons - Constant water and solar radiation - Soils low in nutrients; plants have large leaves and can grow rapidly; dense canopy of evergreen trees leading to low amounts of sunlight Tropical dry forest - Warm to hot year-round - Receives concentrated rain in 3-6 months; very rainy wet season and extended dry season - Deciduous trees allow sunlight to reach the ground during dry season - Soils richer in organic matter and higher in nutrients; rapid plant growth during wet season Desert - Evaporation exceeds precipitation - Low primary productivity since photosynthesis is limited Mediterranean scrubland - Cool, wet winters and hot, dry summers - Ferrel cell influence - Shrubs, small trees and grasses dominate – adaptations to withstand droughts Temperate grassland - Grasses and small shrubs dominate - Often in interior of continents - Temperature varies strongly between seasons; most precipitation during hot summer months; thunderstorms can produce fires eliminating trees Temperate forest - Deciduous trees dominate - Distinct seasonality - Dense canopy intercept sunlight, secondary canopy, then ground layer - Soils high in carbon and nutrients Boreal forest - Characterized by coniferous trees - Strong seasonal pattern to temperature (6 month winters, 2-3 month summers) - Precipitation fairly constant throughout the year Features of aquatic environments - Light and nutrient availability - Temperature - Salinity - Physical movement of water (flow) - Structure of benthic surface - Water depth affecting temperature and light availability - Proximity to shorelines Photic vs. aphotic zone - Photic: “top layer” – sunlight only penetrates this layer where almost all photosynthesis occurs - Aphotic: below the photic zone – light levels are too low for photosynthesis, limiting the number of organisms present Unique properties of water - Universal solvent - Cohesion – hydrogen bonds - High heat capacity - 3 states of matter - Transparency - Density Life history and Trade-offs - Life history: the temporal sequence of events that determines survival and production from an individual’s birth until death - Life history has several key traits: time to maturity, fecundity, parity, parental investment, longevity - Life history is shaped by trade-offs - Trade-offs: balancing of factors not attainable at the same time; giving up one thing in return for another - Organisms made trade-offs to provide themselves with the highest possible chance of surviving and reproudcing - Natural selection is the ultimate judge of this - Overall goal of optimization is increased individual fitness Principle of allocation - All individuals have limited access to energy; energy allocated to one of life’s necessary physiological functions reduces the amount that can be allocated to other functions – allocation indicates priority Mathematical model for energy allocation in plants vs. animals - Animals: E(intake) = E(respiration) + E(assimilation) + E(reproduction) + E(waste) - E(respiration) = total energy devoted to getting oxygen into body/cells - E(assimilation) = total energy converted to living tissue/biomass in organism - Plants: E(photosynthesis) = E(respiration) + E(assimilation) + E(reproduction) + E(waste) Optimal foraging theory - Individuals act to gain the most energy for the least cost when making foraging decisions, with the overall goal of maximizing evolutionary fitness - E(intake) varies and assumes E(respiration) stays constant – want as much energy left over as possible for reproduction and assimilation Simple optimal foraging model for predators and prey - Predator: lion hunting a gazelle - notice the energy it takes to stalk, chase, catch, kill and then eat the gazelle - Prey: the energy it takes for the gazelle to get away, making the lion search and try again and let the gazelle get away again and again - P = E/C - P = the energetic profitability of the prey consumed (equal to the ratio of energy gained from eating that prey item (E) to the energy costs associated with acquiring and eating the prey (C)) - Profitability (P) increases if lots of energy is acquired from a prey item (if the numerator E is big) or if it takes less searching time or capturing energy to get that prey item (make denominator C small) - If P is less than 1, we expect predators never to choose it because it’s not worth their time and energy - C - search costs are primarily a function of prey density; once the prey are found, the predator has to capture, manipulate and consume it - this is called handling costs - P = E / (S + H) r-selected vs. K-selected - r-selected associated with: unpredictable/unstable environments, low competition, abundant resources, disturbed/new habitats, high dispersal, rapid colonization of habitats - K-selected associated with: stable/predictable environments, mature/crowded ecosystems, resource-limited environments, intense competition, maintains stable population size near carrying capacity (K) Root vs. shoot investment - Root investment: - access water and nutrients efficiently - less energy fort shoot growth/photosynthesis - favoured in dry/nutrient-poor soils - Shoot investment: - Maximize light capture and photosynthesis - Less energy to access water/nutrients - Favoured in abundant water/nutrients Water and energy use – principle of allocation - W(intake) = W(respiration) + W(assimilation) + W(reproduction) + W(waste) - Water is not only lost to the environment through metabolic reactions but is also actively used to obtain oxygen for metabolism, to maintain body temperature and/or get rid of waste energy - Unlike with energy, it is possible for an organism to ingest or gain too much water where loss/waste becomes useful Poikilotherms - Don’t regulate internal temperature; allow internal body temperature to follow external temperature Ectotherms vs. endotherms - Ectotherms: regulate internal temperature through thermoregulation using only external mechanisms (moving into the shade or sun) - Endotherms: regulate internal temperature through both internal (e.g. metabolic heat, shivering, panting) and external mechanisms Homeotherms - Endotherms that use metabolic heat to maintain internal temperature at a consistent level (generally have feathers, hair or fur) - Non-homeotherm endotherms generate heat but don’t maintain constant internal body temperature Niche space - 2 physiological tolerances (temperature and dissolved oxygen concentration of water) to construct a graph - A niche space is a region in a multidimensional space constrained by environmental factors that affect the fitness of individuals of that species - The rectangle represents the fundamental/potential niche space the species can occupy - If the organism can’t use all of the conceptual space because of interactions with other species, its niche space is better represented as some subset within the rectangle (dotted oval representing realized niche space) A species’ ecological niche is defined as an n-dimensional hypervolume where n indicated the number of dimensions (different environmental conditions) that determine where an organism can survive; a hypervolume is a space defined by more than 3 axes Extremophiles - Organisms able to live in extreme conditions; often require extreme/specialized adaptations - E.g. high temperatures have heat-resistant enzyme, desert organisms conserve water (cacti), antarctic organisms manage freezing temperatures (produce antifreeze) Range of tolerance - Ecological tolerance is the ability of an organism to endure under certain environmental conditions - Each organism has limits to tolerance, below or above which it cannot survive Fundamental vs. realized niche - Fundamental: range of abiotic conditions in which a species can potentially survive and reproduce (no biotic constraints such as competition and predation); shaped by tolerances  - Realized: actual range of conditions and resources that a species occupies in the presence of biotic interactions and competition (biotic constraints such as competition and predation) The actual range of environmental conditions depends on biotic interactions (can contract or expand a species’ range of tolerance) Niche overlap - Occurs when multiple species share similar ecological requirements, potentially leading to increased competition - Often influences the realized niches of one or both of the species Resource partitioning - The division of limited resources among coexisting species to reduce competition - Shapes the realized niche and facilitates coexistence WEEK THREE Populations - A group of individuals of the same species that is spatially distinct from other groups of individuals of the same species Mark-recapture sampling - Capturing, tagging and releasing individuals and then resampling; if the tags are unique and allow distinguishing between individuals, recapturing tagged individuals provides information on individual growth, movement and behaviour - Way to estimate overall population abundance Discrete-time population growth model Geometric - Reproduction occurs at regular time intervals - Population increases by a fixed proportion λ over discrete, non-overlapping time intervals - Used to model populations with discrete breeding seasons or generations - λ = 1 + (b-d) (λ is the finite rate of increase; λ = 1 means no change) Exponential - Occurs when reproduction occurs continuously (e.g. humans) - Population increases at a rate proportional to its current size - r = b - d (r is the intrinsic rate of increase; r = 0 means no change) Similarities and differences between geometric and exponential - Both have an intrinsic growth rate (λ or r) - Both show rapid growth due to multiplication - No limiting factors Intrinsic rate of increase vs. finite rate of increase Life history Survivorship curves - Type I: individuals have a high rate of annual survival until they reach old age, when mortality increases dramatically (e.g. humans, whales, elephants) - Type II: mortality rate doesn’t change with age - Type III: individuals have a high chance of dying in the earliest part of life but have higher rates of survivorship after the juvenile period Age vs. stage structure - Humans have a distinct age structure – survival and annual fecundity rates vary with age group - Maturity can affect survival/reproduction without being strongly tied to age - this is referred to as stage structure (individual differences in reproduction and survival vary by life stages) Population abundance and density - Abundance: refers to the total number of individuals of a species in a given area - Density: refers to number of individuals per unit area or volume – useful to understand spatial relationships Different methods for estimating population size - Quadrat: area-based count - Transect: start at one point and then walk __ metres and count - Remote sensing: send out drone and then use AI or count Patterns of dispersion - Clumped: clustered together in groups within a population - Uneven distribution of resources - Due to social behaviours, mating - Uniform: evenly spaced throughout the population - Associated with competition for limited resources - Associated with territorial behaviours and antagonistic interactions - Allelopathy: releasing chemicals into environment influencing growth, germination or development of nearby organisms - Random: distributed without any specific pattern or order - No strong attraction/repulsion between individuals - Random dispersal mechanisms Liebig’s law of the minimum - Growth is dictated not by total resources, but by the scarcest resource - Rate of biological process limited by that factor in the least amount relative to the organism’s requirements BIDE model - Births, immigration, deaths, emigration - Rate of increase (maximum rate at which a population can grow under ideal conditions – r or λ) Time series - A sequence of data points collected over time to study and analyze population size Logistic model - The most common model for negative density dependence - S-shaped curve - Has a distinct inflection point – the point of fastest growth after which growth begins to slow (exponential before this point, logistic after) - Growth eventually falls to zero - K is the carrying capacity - the point at which growth rate becomes negative; the maximum number of individuals that can be supported by the available resources in a particular environment (often due to intraspecific competition at higher population densities) Density-dependent factors limiting a population - Biotic factors (competition, predation, parasitism, disease) - Abiotic factors (temperature, precipitation, sunlight, pH) - At higher population densities, there is often intraspecifc competition - As a population gets bigger, there is more demand for a limited number of resources (either death rates increase, birth rates decrease or both) Negative density dependence Positive density dependence (aka Allee effect) - The growth rate or survival of a population increases as the population density increases - Not due to limited resources, but instead due to: - Finding mates - Cooperative behaviours - Predator satiation - Resource availability Density-independent factors limiting a population (affect the population regardless of population size) - No clear pattern over time - Due to stochasticity (disease, natural disasters, human disturbances) - Can increase or decrease population size Overshoot - Occurs when a population exceeds its carrying capacity - Demand for resources increases -> decrease in birth rates, increase in death rates leading to die-off Monotonic damping - Smooth approach to carrying capacity; low growth rates Damped oscillations - Regular fluctuations that decrease over time - Population grows beyond carrying capacity and then dies off and then goes up again; over time, population approaches carrying capacity and eventually levels off Stable limit cycle - Regular fluctuations consistent over time - Population increases -> overshoots -> die-off -> drops below carrying capacity and continuously cycles this way - Associated with even higher growth rates Chaos - Unpredictable and irregular fluctuations - Happens because of the growth rate – jumps all over the place Fluctuations in population size - Can be regular (seaonsal changes), irregular (non-seasonal changes), cyclical (intrinsic factors, species interactions) - Small populations are more vulnerable to environmental changes and stochastic events; greater risk of extinction  - The stability of a population is maintaining constant population size over time within a given area Coefficient of variation - Measure of the relative variability around the equilibrium - Low CV = more stable, high CV = less stable Perturbation - Any temporary or permanent change in the conditions in an ecosystem that disrupts its normal functioning or structure - A population that returns quickly after a perturbation is more resilient - Populations with low growth rates have long return times making them more susceptible to subsequent perturbations WEEK FOUR Mutualism - Occurs when both species benefit from their interaction Exploitation - Occurs when one species benefits at the expense of the other - Predation, parasitism, herbivory Competition - Occurs when both species are negatively affected by the other Commensalism - Occurs when one species benefits while the other in unaffected Amensalism - Occurs when one species is negatively impacted while the other is unaffected - E.g. elephant crushing a plant while walking Neutralism - Occurs when neither of the 2 species is affected by the other Intraspecific competition - Competition among individuals of the same species in a single population, with respect to limited resources and carrying capacity (K) Interspecific competition - Competition for resources among individuals of different species - 2 types: - Resource competition (exploitative competition) occurs when individuals of one species more efficiently consume or use up a shared resource lowering the availability for individuals of other species, affecting their fitness (sometimes referred to as indirect interaction) - Interference competition occurs when individuals directly interact with each other through aggressive behaviour to increase access to a limiting resource  - Also: apparent competition – indirect interaction between species in which the presence of one species negatively affects the population growth/fitness of another through a shared predator Resource utilization curves - Explore overlap in resource use by 2 different species; species use the same resource but don’t overlap in the exact type of resource needed - When no overlap – no competitive effects; minimal overlap – small negative effects for each species - Substantial overlap – presence of one species will reduce availability of resources for other species affecting survival, reproduction and population growth Competitive exclusion principle - When 2 species substantially overlap in ther resource use, even a slight disadvantage in acquiring resources will impose fitness costs on individuals of the other species and drive the second population extinct; 2 species can’t coexist due to competitive interactions - Leads to extirpation or local extinction - If the resource utilization curve for 1 species sits inside that of another, then that species using the larger resource pool should persist and use up the carrying capacity of the other Competition coefficient - Quantifies the intensity of competition between species for a shared limiting resource (quantifies the effect of one species on another, describes how the growth of one species is affected by the abundance of another species) - In the Lotka Volterra two-species competition model, we can’t assume that 2 competing species will have the same carrying capacity even when using the same resources because they each have different fundamental niches and the carrying capacity for each species is in units specific to that individual species Experiment to test the type of competition taking place - Microcosm/mesocosm experiments: 2 species separately and together - Removal/addition field experiment: ‘transplant’ experiment - Observational studies: infer the presence/effects of competition (not evidential) - Resource manipulation experiments: - Determine if exploitative competition is taking place; treatments with different quantities of a shared resource, ensure no physical interference - Direct interaction experiments: - Determine if interference competition is taking place; treatments with different quantities of a shared resource; species either allowed/not allowed to interact Niche overlap - The extent to which the ecological niches of 2 or more species in a community share similar resources Niche/resource partitioning - Exploit different resources in some way that each species specialized on a different resource or in a different location (outcome of coexistence) Character displacement - Competition between similar species leads to evolution of distinct differences, reducing competition (outcome of coexistence) Types of niche differentiation - Spatial niche differentiation: species differentiate in the way they use a resource - Resource/prey niche differentiation: consumers may be better competitors on different resources; a differential ability to exploit different resources - Temporal niche differentiation: species differentiate in the way they use a resource by exploiting it at different times (of day, different seasons) Phase planes - Provide a way to visualize how populations of species change over time and interact with one another - Each axis represents the size of a population/species Isoclines - Lines on a graph that indicate where the population growth is zero for one or more species (represents zero population growth) - On the left side, there is no interaction with the other species and the number increases towards the line; on the right, the number will decrease towards the line - At any point of the isocline, the growth rate of the species is zero - Position/shape is determined by carrying capacity and coefficients WEEK FIVE Exploitation - An interaction in which individuals of one species increase in fitness by consuming individuals of another species, who experience a decrease in fitness Predation (carnivory, cannibalism) - Carnivory - the predation by animals consuming other animals - Cannibalism - predation by an organism on individuals of its own species Parasitism (macroparasites, microparasites, parasitoids, hyperparasitoids) - Parasites obtain energy and nutrients from their hosts by attacking the host’s body or organs and consuming tissues or fluids, often without killing the host; each parasite tends to use only one host for its whole life - Macroparasites are larger such as worms or ticks, they live on or within a host to derive nutrients, but don’t multiply within the host - Microparasites are microscopic like bacteria or viruses, that reproduce rapidly within their host, often causing short-term infections - Parasitoids are typically insects that lay eggs on or within a host, eventually killing the host as their larvae develop and eat it - Hyperparasitoids parasitize other parasitoids, exploiting the parasitoid and its host Herbivory (grazers, browsers, phytoplankotvores) - Exploiters consume plants, they don’t typically kill the plants they eat - Grazers feed on low-growing plants - Browsers feed on high-growing plants  - Phytoplanktivores eat phytoplankton - Frugiovores eat fruit - Granivores eat grain - Nectivores eat nectar - Folivores eat leaves - Xylophages eat wood - Rhizophages eat roots Generalists vs. specialists - Generalists consume a variety of resources - Specialists consume a limited number of resources Top-down regulation vs. bottom-up - Top-down: consumers regulate abundance of prey - Bottom-up: availability of resources influence abundance of consumers 4 outcomes of exploitation 1. Prey extinction leads to predator extinction 2. Predator extinction with surviving prey (low prey density; prey sought refuge and predators couldn’t find them) 3. Exploiter-prey cycles 4. Stable coexistence Lotka-Volterra predator prey model Variables N is prey biomass (resource) P is predator biomass (consumer) Parameters r is the intrinsic growth rate for the resource f is the capture rate (efficiency) of the predator on the prey c is the conversion efficiency of the predator d is the mortality rate of the predator Exploitation isoclines - Black star: both populations crash to extinction - Gray star: prey crashes, so predators crash - Green star: unchecked prey population growth, with exploiters going extinct Exploiter functional responses - Type I: constant linear increase with prey density; predators don’t face handling constraints and consume prey at a constant rate; sometimes saturates at high prey densities - Type II: shows plateauing effect, rate increases with density, slows down and plateaus at higher prey densities; predators have limited handling capacity or encounter prey defences - Type III: shows a delayed increase followed by a plateau (sigmoid curve), low prey consumption under low prey densities, rapid increase at moderate prey densities, plateaus at high prey densities; predators show prey switching, spend time searching for and capturing prey; prey hide or are difficult to catch at low density and seek refuge Allee effect (aka positive density dependence) - Fitness declines as density declines - An aggregation of a large population reduces any single individual’s chances of being consumed; this can lower attack and capture rates Phase plane analysis of the Allee effect - 3 outcomes: 1. Stability 2. Extinction  3. Cycles Primary, secondary and tertiary defence strategies - Primary: not be seen in the first place (camoflage or crypsis – mimicry) - Secondary: once spotted by prey, announce themselves as something else and mimic other species - Tertiary: involves a way to escape or fight off an attack; physical defence or staying in place (hard shells) /playing dead Interaction strength - The magnitude of effect that one species has on another species in a community (pairwise interaction) Mathematical model of competition - Competition coefficient quanitifies the intensity of competition between species for a shared limiting resource Mathematical model of consumer-resource interactions - Measure of how good the predator is at turning the energy from eating prey into growth - Higher conversion efficiency = predator gain Principle of interaction strength - When interactions between consumers and their resources become stronger: - More consumers relative to amount of resources - System becomes less stable (populations likely oscillate) - Consumers and resources are more likely to go extinct Weak interaction effect - Is a hypothesis: if weak interactions stabilize food webs, then weak interactions will be common in ecosystems and strong interactions will be rare - When one resource is low, the predator can switch to an alternative resource (prey switching) which is less likely to drive a low abundant resource extinct Close to 0 = weak Away from 0 = negatively or positively strong Measuring interaction strength: - Direct observations: attack rates and biomass flux - Statistical models: covariance of populations - Experimental manipulations WEEK SIX Facilitation vs mutualism - Facilitation: an interaction between 2 species that benefits at least one of the species - Mutualism: facilitation that benefits both species (ecological equivalent of trade; form of niche differentiation) - Not instances of altruism - the goal isn’t to benefit the other species Obligate vs. facultative mutualism - Obligate: necessary for the survival of at least one of the participating species; highly species specific - Facultative: benefits both species but aren’t necessary for the continued survival of at least one participating species (take it or leave it); less species specific Partner specificity - Refers to how selective or flexible the participating species are in a mutualistic interaction; highly specific (interact with one or few partner species) or generalized - Highly specific mutualisms often involve coevolution - Generalized mutualisms allow for more flexibility and resilience to environmental changes Symbiotic interactions - A type of mutualism in which individuals live within or on the other organism; can range from parasitic to mutualistic - Characterized by close physical contact: endosymbiosis (lives inside) or ectosymbiosis (lives on) Trophic mutualisms (benefit of mutualism) - Trade food for nutrients or for other food (energy) - Nutrient exchange, provide sugars, etc. Defence mutualisms - Trade defence for energy - e.g. one species protecting another and offering food rewards/shelter in return Transport mutualisms - Trade transport for energy (i.e. seed dispersal and pollination) Mutualism parasitism continuum - The strength of mutualisms depends on the conditions that motivate the trade - Mutualisms can become parasitic if the cost of the trade outweighs the benefits Conceptual model of mutualism - Any model of mutualism needs to show a positive interaction - For mutualisms, we flip the competition interaction since species two has a positive effect on species one and vice versa; increases carrying capacity Facilitation - An interaction between 2 species that benefits at least one of the species (e.g. mutualism and commensalism) Foundation species vs. keystone species vs. dominant species - Foundation species: provide an ecological foundation for many other species, even if they might not benefit from the interactions; often a dominant species - Keystone species: has a disproportionately large impact on its environment relative to its abundance or biomass - Dominant species: an abundant species exerting significant influence on other species within the community or on the structure/function of an ecosystem Ecological restoration - The process of assisting the recovery and re-establishment of ecosystems that have been degraded, destroyed or damaged - Include facilitative and mutualistic species - Positive feedback loop to help new species establish by adding in foundation species Invasional meltdown - The introduction of one invasive species facilitating the establishment and spread of additional invasive species - Multiple invasive species causing significantly more damage together than alone and hasten the degradation of invaded ecosystems - Positive feedback loop allowing new invasive species to establish by adding in invasive species