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Ecology Lectures (2-12): Lecture 2: Population Sizes and Density Patterns The ubiquitous quadrant: form of measurement used in Ecology to sample a population and make assumptions about it. Pros: meters squared is convertible and scalable Cons:
- Assumes more stems mean dominance
- Certain species of plant especially ones with shoots are assumed to be one plant although shoots eventually form new plants
- This system can be difficult when you have to account for mobility of certain species within the frame of reference
- Depending on sight ability counting within the designated mark can be challenging Overview: Need to find a way to adjust for the “individual” and a way to adjust for sightability Field Methods of Counting Species and Populations:
- Bound: a. Defining an area with a limit (use of the one quadrant to count the population within a certain space) b. Percent cover: to take one sample of a species and decide what percentage of space the specimen takes up relative to the whole space ( Accounts for not only individual stems but also colonial species. Colonies, stems with broad leaves, genet (ramets) ) i. Braun-Blanquet: based on a specific scale where percentages are given values (+ to 5) – a very loose approximate Index of dispersion: measure used to quantify whether a set of observed occurrences are clustered or dispersed compared to a standard statistical model. Used for density patterns of population. Important conversions: 1 ha = 10000 m 1km2 = 100 ha
- Unbound: (no frame) a. Line transect: count species within a boundary and outside a boundary (given two separate values – which will give you a density value
i. An arbitrary value is something that defines how far you look to get the N1 value (ex. The red on the red-winged black bird) b. Plotless: put a tape measure (should be close to 100ft long) around an area with the counted species. On the tape measure, put a minimum of 50 random points. From each random point, measure the distance to the closest specimen (which you take the average distance of all points measured – which will give you the estimated density of the population) i. To correct bias: this method can overshoot the estimation of the population. To correct the bias, measure the distance from the plant associated with the random point to the nearest neighbor plant
- Indirect Mark and Recapture: Distribution and Abundance Patterns:
- Spatial borders where population is found – the geographical range
- Population dispersion – index of dispersion (variance/mean) o If the index of dispersion is greater than one, the population as a whole is “clumped” – gives us an idea of what kind of ecology is driving the species o Three reasons why a population could be clumped: Intraspecific Aggregation (schooling) – can be an anti-predator defense Habitat Selection – predator avoidance and food (for example, can hide within patch reefs as a defense mechanism). Can also be for mating sites Interspecific Competition – between different species o If the index of dispersion is less than one, the population is “dispersed” (uniform) o What ecological mechanisms can drive a population to be even and dispersed? Intraspecific competition for limited resources – the same species is fighting for the same resources (for example: food and habitat) o If the index of dispersion is equal to one (or very close to), the population is considered to be “random” o What ecological mechanisms can drive a population to be random? Its and accumulative bunch of multiple mechanisms Lecture 3: Population Dispersal and Metapopulations
Metapopulations – The Influence of Landscape Structure on Dispersal
- Species are viewed as a collection of populations: each existing on a “patch” of suitable habitat, separated from other patched by unsuitable terrain
- Long-term persistence: the balance between local population extinctions and founding of new populations via dispersal
- Four models of metapopulations: o Occupancy Model, Classical o Core-Satellite (Mainland-Island) o Patchy o Source-Sink Lecture 4: Growth Regulation
- The size of any population in ecology is determined by two opposing factors o Biotic Potential (growth) That is the capacity for the population to grow Maximum rate population can grow assuming maximum birth rate and minimum birth rate Ex: Petri dish of bacteria and you grow the bacteria. If the bacteria reproduces by binary fission every 20 mins it would take the bacteria 48 hours to consume the planet assuming that they had unlimited resources (times the population by 2 every twenty minutes) Model 1: Geometric Density-independent Unlimited environment Non-overlapping generations (ex: discrete/pulsed reproduction; t= num. generations) Generation reproduces and dies (doesn’t continue to stay alive after reproducing = no overlap of generations) Each population generation will double Nt = No*Lambda ^ t Lambda = geometric rate of increase (average number of offspring by an individual) For no change in population size (Nt = No) then lambda is equal to 1 Model 2: Exponential Density-independent Unlimited environment Overlapping generations (continuous)
Ex: Eagles Start with one pair of eggs Need to be 4 years old to reproduce They can only reproduce every 2 years after that Nt = No*e^rt This is because you want to be able to predict the future populations R = per capita (per individual) intrinsic rate of increase Similar to Lambda t = years For no change in population size (Nt = No) r will be 0 o Environmental Resistance (resistance to growth) Interaction between Density-independent factors (ex: factors reduce population growth without regards to size) such as: Weather Fire Earthquakes Density-dependent factors (ex: exert negative feedback; become increasingly effective as population density increases) such as: Intra & interspecific and exploitative & interface competition Predation & parasitism Density-independent factors:
- Exploitative competition o If both individuals (with from same and different species) draw from shared /limited supply, then with members weakened Ex: Grasshoppers. Inside grasshopper cages, there are natural grasses growing and in each, there is a different number of grasshoppers. This means that regardless of the density of grasshoppers, they are all starting off with the same amount of food. Looking for the growth rate of grasshoppers in comparison of the density. The idea is that they will be fighting each other for food, the higher the density
- Interference competition o Individuals acquire resources at expense of others o Clear winner and loser Ex: Birds and predators As the bird population increases, the density increases but the quality of the habitat decreases because of competition
- Ideal Free Distribution o Assumes as population density increases -> fitness decreases
o Continue with the abundance (Nx) o Then do the Log(Nx) o Then do the k-value (killing value) -> the difference between the value of the answer of Log(Nx) Trying to figure out which of the mechanisms of killing has the biggest impact on the species o Survivorship (lx) Proportion of individuals born who survive to age X Lx = Nx/No o Fecundity (Fx) Average number of female babies born to a female mother in each age group o Net Reproductive Rate (Ro) Average number of female offspring produced per female offspring produced per female during her lifespan Ro = the sum of lx*mx o Rate of Increase (r) Per capita growth rate ex: instantaneous rate of change of population size (per individual) r = ln(Ro)/G r > 0 then population is growing r = 0 then population is stable r < 0 then population is declining Static Life Table (~vertical, time specific) You are not responsible for the mechanics of this life table o Record age at death of large number of individuals o Need “graveyard” Lecture 5: Physical – Terrestrial
- The atmosphere is composed of four different levels: troposphere, stratosphere, mesosphere, and the thermosphere (each are biologically important to ecology)
- When talking about climate, the main changes in effects occur within the 10-20 km
- Temperature: closer to the Earth more molecules collide causing heat, as you increase the height, closer to the top of the Troposphere, less molecules are present, meaning less collisions and less heat.
- The Environmental Lapse Rate: the temperature drops for when the height of the atmosphere is increased. o Average: Decrease of 4°C for every 1000 m)
- The Sensible Heat Flux: the transfer of heat via convection and conduction
- Latent: the transfer of heat via evaporation
- Other means of heat transfer: released as thermal energy that hits the ground to create strong heat for the environment o UVA o Visible o Infrared
- Adiabatic Expansion: When the radiation hits the ground, it creates thermal energy, which is then released through longer waves, which heats up the ground creating an air mass. This air mass is heated causing the molecules to move a lot faster, pushing the air mass bigger (making it less dense and causing it to rise) o Dry Adiabatic Lapse Rate: As the air mass rises and expands it cools at a rate of 10°C for every 1000 m.
- When the air mass rises its called uplift (low pressure cells) and after it cools, it descends, known as subsidence (high pressure cells)
- In the stratosphere, the temperatures warm up – UVC radiation is absorbed (when combined with oxygen, it splits up oxygen into free radicals – which react with other oxygen molecules to create ozone, which is an endothermic reaction) o UVB reacts with ozone to split it into oxygen and free radicals, and exothermic reaction (produces more heat than the UVC reaction)
- In the mesosphere, the temperature decreases, but increases with Gamma rays (react with molecules) in the thermosphere
- Coriolis Effect: an effect whereby a mass moving in a rotating system experiences a force acting perpendicular to the direction of motion and to the axis of rotation.
- Conveyor belts surround the Earth – are split into small pieces: o Hadley Cells - Northeast Trade Winds o Ferrel Cells – Westerlies o Polar Cells – Polar Easterlies
- When the air masses are in uplift (between Hadley cells) there is a creation of hot and wet rain (mainly over the dark green bands of land in the Earth)
- When the air masses are decrease, the air masses form the desserts (hot and dry deserts) between the Ferrel and Hadley cells
- Flow is unidirectional (ie. downriver)
- Continuous physical change o If a river is isolated, there are three main systems: Headwaters: water drains of the physical landscape from terrestrial to aquatic Transfer Deposition: when the river enters the body of water, the movement of the river slows down when it goes into a larger body of water o The slope of a river is highest at the headwaters and progresses to a gentle slope at the deposition (slope is x=0) o The bed material size is larger at the headwaters because of all of the larger rocks, and lower at the deposition with sand and clay that is washed in from the river o The volume of stored alluvium: the thickness of the bottom of the river: smaller at the headwaters, and as you make your way to the zone of deposition, the volume is increased
- Energy Input – allochthonous and autochthonous o Headwaters: huge amount of tree coverage limits the amount of sunlight to the water – limited to the high noon (overhead sun) Autochthonous: source of energy from the sun that drives photosynthesis (very little in the headwaters, due to the lack of sun) A biofilm grows on the rocks, causing them to be slippery (ex. algae) – grazers, like snails enjoy the biofilm (very little biomass of grazers) · Scrape the periphyton (the cyanobacteria) off of the rock surfaces Allochthonous: the leaf litter (energy) that falls into the river, which gets decomposed and becomes a food source (the primary source of energy) · Shedders (huge amounts) chew and rip apart the organic matter from the decomposing plant tissue (ex. stoneflies and sowbugs) Photosynthesis vs. Respiration (breakdown of other food sources): PS/R · Greater than 1: photosynthesis is favoured · Less than 1: Respiration is favoured · For headwaters: since there is more energy being produced by allochthonous, there is more respiration meaning the value is less than one
Oxygen and Temperature: highly oxygenated (due to rainfall), and because they are in the shade, the temperature is average (on the cooler side) o Zone of Transfer: Water is shallow and wide – a lot more sun is directly on the water, causing an increase in temperature – Oxygen will be higher because the river is wider causing a good flow and exchange of oxygen When the water transfers from the headwaters to the zone of transfer, there is a lot of broken-down food pieces being carried into the water · The collectors (large volume of them) help to filter feed on the organic matter transferred from the headwater · Grazers also are included in the zone of transfer, since there is an increased surface area, there is more sun and therefore more photosynthesis · Predators (like dragonflies) also are increased in the zone of transfer. They attack prey by injecting enzymes to paralyze There is more photosynthesis (value is greater than 1) in the zone of transfer o Zone of Deposition: Because of the water coming down, it contains sand and clay making it very cloudy, the sunlight does not penetrate. The oxygen is not produced (deeper causing a lack of exchange of oxygen), and the temperature is low because of the depth of the water Scavengers: increased amount of them – going after dead fish (larger items) Collectors: go after the smaller items being washed down o Respiration is favoured (meaning the value is less than one)
- Spatiotemporal Heterogeneity (always changing) o There is not one point from the changing states of the river where you get the exact same values, they are always changing
- Species Responses – River Continuum Concept o Based on the species in each part of the river, who dominates the most? o As you make your way down the river the domination of each species changes, shift in the proportion of species o The physical spatiotemporal heterogeneity drives the species richness patterns (RCC) Section B: The Lentic System (ie. lakes)
Since water is buoyant, the hotter water stays above the cooler water (water is at its most dense at 4°C – sits on the bottoms of the lake – aka. the hypolimnion) Above the hypolimnion, is the thermocline, which is the barrier between the warm and cold water The epilimnion: the warmer water towards the surface o Differentiation in species based on the temperature of the water: Cold water: salmonids Warm water: centrarchids o Based on the temperature of the water, the barrels roll and rustle up algae, creating a foam on the surface of the water o In the benthic biome of the lake – inclusion of plants (no nutrient value) Lecture 7: Species Interactions – Predation
- Carnivores have a broad diet compared to herbivores that have a narrow diet (very specialized) Avoidance Mechanisms:
- Avoid Detection: o Cryptic camouflage and Cryptic Behavior: only works if the behavior is suitable to the camouflage (ex. if a man is standing in front of a display and is painted to blend in, but is only able to not be seen from certain angles) § To enhance cryptosis: · Counter shading - makes it harder for the predator to see the pray (which appears flat and one toned) · Flanging and Fringing – the body extends and creates a smaller shadow; the fringe breaks up the shadow o Masquerade: hiding in plain sight as an inedible object (ex. the Potoo’s become part of the tree, staying motionless) o Disruptive: high-contrast dark and light patches in a non-repetitive configuration that provides camouflage by disrupting the recognizable shape of the animal.
- Ward off the Attack: o Aposematic: bright colours (warning colour) warns predators that a certain prey are toxic
o Batesian Mimicry: one species mimics the other, the model has the toxicity, the mimic looks similar but is not actual toxic, still wards off the predators o Mullerian Mimicry: similar to batesian mimicry – the species can morph into another species that is toxic and prevent being hunted (both species are toxic) – shared defenses (all models) o Mertensian Mimicry: similar species with different toxicity levels Ex. The false coral snake is a model for the Texan coral snake (the mimic). If you get bitten by the false coral snake, you will get sick causing you to learn not to go after anything looking similar (including the Texan coral snake which is deadly) o Pursuit-deterrent Signals: the prey lets the predator know that it has been spotted o Physical/armour: hard shell on animals (like turtles) to not be able to be eaten by the predator Plants can also have armour: thorns, prickles, and spines o Thanatosis: aka. “playing dead” – a large number of predators will not consume prey they have not killed themselves o Distraction: False display of anatomy (ex. on certain fish, it looks as though there is eyes on the back of the fish, giving a false swimming direction) o Startle Behavior: a momentary reveal of a threat (for example: the silk month reveals a large pair of dots on its second set of wings, making the predator think it has eyes staring right at them – which will scare them off) o Intimidation Display: a motion that reveals an intimidating feature (for example: when a predator is coming after a mantis, the mantis will lift its arms, showing red and intimidating the predator, scaring them off) o Chemical: production of chemicals that is sprayed onto the predator (ex. the bombardier beetle shoots acid out its butt at 100°C) o Autotomy: cutting off the limb in order as an escape mechanism o Evisceration: to vomit out the insides of an organism through the butt (the sea cucumber shoots out its tubules, tangling the predator, while the prey gets away) o Phagomimicry: to mimic the food – for example: when a dye is ejected from the squid, the predator is visually impaired. § In the dye, the opaline amino acid mimics food, allowing the predator to stay in the source of the dye, while the prey gets away.
o Phaeophyta (brown) o Chlorophyta (green) There are over 5000 species of macroalgae in this biome
- Herbivores eat the algae located in the coral reefs: o Diurnal vertebrates (fish and sea turtles) o Nocturnal invertebrates (gastropods and sea urchins) Over 60+ different types of herbivores feeding 24hrs a day (over 99% of algae production is eaten each day)
- There are over 5000+ species of algae split into six functional groups based on similarities in: o Nutrient uptake rates o Productivity o Turnover rates o Resistance to herbivory * The Six Functional Groups:
- Filamentous (delicately branched)
- Foliose (leafy/ sheet-like)
- Coarsely Branched
- Thick Leathery
- Jointed Calcareous (upright, coarsely branched)
- Crustose Coralline (prostrate, tough, and stony) Macroalgal Defenses of the Six Functional Groups:
- Herbivores have a very specialised diet – need defense mechanisms *The darker the colour, the more important that defense is to each specific functional group Functional Group Structural Refugi a Associati ve Growt h Chemical (Constitutiv e) Chemical (Induced) Mineral s
Filamento us Fine and delicate with no structural defense (no defense) Algae will often take “cover” by staying close to the coral – a refuge from herbivory pressure Fine filaments of algae will stay sheltered from herbivory pressure by interwinding in a plant that is poisonous (sargassum network) Algae grows FAST – this is the primary defense mechanis m – it is cropped down daily by the fish, but the roots are protected (no defense) (no defense) (no defense) Foliose The underground rhizomes link all the beads together (above the sand) via connective tissues (are not eaten by herbivores) Morphological plasticity: when there is high herbivory pressure, the blades are denser Herbivore s are easy prey to predators, naturally they hide. The algae is out in the open, and most herbivory fish will not swim without shelter as they might get eaten by predators The foliose algae will often grow within a calcareous alga to protect itself against predators. The predators will not go after the leafy algae. Moderate growth (not a major defense mechanis m) Include secondary metabolites: terpenoids and stypoldiones are stored inside tissues that are toxic to herbivores Constitutive means that the chemicals are part of the algae’s tissue (no defense) (no defense) Coarsely Branched The course branches make it difficult for animals to access them (most of the urchins) (no defense) (no defense) (no defense) Pump tons of secondary metabolites into their tissues that warn off (are toxic) to herbivores (minimal defense) (no defense) Thick Leathery Thick leaves, tough and hard to rip (works well as a defense) (no defense) (no defense) (no defense) Have tons of secondary metabolites that warn off and are toxic to predators Have induced metabolites: the chemicals produced are so toxic, they are sometimes toxic to the plant itself (not always present – only through the presence of herbivory action will the toxin be released (no defense)
o Enzymes from the herbivore react with enzymes in the plant, releasing a volatile chemical that floats away into the air (the Semiochemicals). All the chemicals floating in the air attract the wasps allowing them to find the specific plant with herbivory action. The wasps then find the herbivore releasing its eggs and killing the herbivore Lecture 9: Species Interactions – Cycles Effects
- Lokta-Volterra (1920): o Two participants: the snowshoe hare and the lynx (predator-prey interaction between the two) o When the Hudson’s Bay captured animals such as the hare and the lynx, they kept great records, this allows us to see the relationship curve between the predator and prey As the hare population increases, so does the lynx (seen by the curves) o Hypotheses: Sunspot Hypothesis: idea that the sun goes on its own cycles – changes the amount of solar radiation. This is the hypothesis that plants depend on the amount of solar radiation (ie. more solar radiation, more plant growth). Since more plants grow, herbivores (ie. the hare) population and therefore the predator (ie. the lynx) population will also grow (the bottom up model) Overpopulation Theories (intraspecific competition): as the population of the hares increases, they will begin to overeat the resources (ie. begin to have limited resources, whether it is food, shelter, environment, etc.), which will eventually make the population decreases due to over exploitation of resources (the lynx population will follow the hare population) Predation Hypothesis: as the number of hares increase, the predator population will also increase, driving down the prey population (the food source), making the predators population also go down in numbers
- This theory can be calculated through the following equation: (for the prey)
- The above equation: ‘r’ is the intrinsic rate of increase (for the prey), ‘N’ is the population size of the prey, ‘a’ is the search and attack efficiency of the predator (how often do they find the prey and are able to attack), ‘P’ is the predator abundance o When the effects of the prey are larger than that of the predator, there is an increase in growth o When the effects of the predator are larger than that of the prey, there is a decrease in growth o If both are equal, the growth is zero (as seen by the peaks and declines in the graph)
- This theory can also be calculated through the following equation: (for the predator)
- The above equation: ‘a’ is the search and attack efficiency of the predator, ‘N’ is the population size of the prey, ‘P’ is the predator abundance, ‘b’ is the amount of prey converted into predator offspring, and ‘m’ is the predator mortality rate. o When a predator is more efficient in producing large amounts of offspring, the population increases, compared to mortality of the predator, which will decrease the population
- On a graph of Nprey vs Ppredators , when r/a is a straight line (zero growth isocline): o Below the line, there are fewer predators – the prey population would increase slowly, the smaller number of predators, the faster the prey population will increase o Above the line, there are more predators – the prey population will decrease
- On a graph of Nprey vs Ppredators , when m/ba is a straight line (predator growth is equal to zero): o If there are more prey in the system, the predator population will increase (the more prey in the population, the faster the predator population will grow) o If there are less prey in the system, there is not enough prey for the predators to feed on, and therefore a decline in the predator population will occur as well (the less prey, the faster the predator population will decline)
- In a homogeneous lab environment – the predator-prey always leads to predator and prey extinction
- To maintain the predator-prey cycle: o Heterogeneous environment (the landscape is variable relative to the two species) – allows prey to hide in order to recover after predator attacks o Predator-prey refuge zones (ex. corals provide coverage for little fish from predators) o Multiple interacting mechanisms Ex: As hare populations increase, herbivory induces chemical defenses (terpene) in plants. As time progresses and the hare population increases, plants induce those secondary metabolites (the ones that are toxic to the predators) causing the hare population to level off. The prey (the hare) becomes more accessible to the predators in the system, causing the hare population to rapidly decrease (this is accelerated because of the high predation rates) Effects of Predators on Communities (case studies):
- The case study of Borneo:
