UGA Plant Ecology Final Exam Study Guide Pt. 1, Study notes of Biology

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PBIO Final Study Guide Intraspecific Competition (competition within the same species) - Competition: a reduction in the fitness of competing individuals due to the sharing of a limiting resource - Resource: something required for growth, maintenance, or reproduction, and which is consumed - Competition among plants is usually very localized, and effects of neighbors decreases rapidly with distance - Resource reduction : to what level can plants of that species reduce resources if they are allowed to grow and take up all the resources they want - R*: the level to which a species can bring down a particular resource - Different species have different R* for one resource; also one species will have different R* for different resources (ex. light vs. nitrogen) - Better competitors are the species that can bring down R* the most - Continuous Population growth - Continuous Logistic equation : dN/dt = rN (K-N / K) - r: the intrinsic rate of population growth - K: carrying capacity - Allows for the growth rate to decrease as population reaches the carrying capacity (birth rate decreases/death rate increases) - This formula gives the instantaneous rate of population growth; it is used for populations with continuous growth - Implies that resources are finite (not unlimited), and makes the population growth density-dependent - Discrete population growth - Discrete : N(t+1) = λN(t) - OR: N(t+1) = N(t) + r(d)N(t), where λ = 1 + r(d) - Logistic discrete equation: N(t+1) = N(t) + r(d)N(t) (K-N(t) / K) - Population growth will stop when N = K, and no matter what the starting size of N, it will move towards K - Thus, K is an equilibrium point (at that moment, population is neither increasing nor decreasing) - Equation Shortcomings: Even after adding density dependence, the equation d oes not consider biomass or plant size, and it implies that all plants are identical - These equations may apply better to unitary, mobile animals, rather than modular, sessile plants - Adding time-lagged equation: - dN(t) / dt = rN(t) (K-N(t-τ) / K) - The time-lagged version of the equation can produce a variety of fluctuating population dynamics; fluctuations are larger when r or τ are large - Adds realism to equations - Logistic equation problem: K - K is not the same for a population of plants with an average size of 100 g vs a population with an average size of 1000 g - Constant final yield : asymptotic relationship between plant density and yield (mass per unit area) – once above some low density, mass per unit area is constant (relationship between biomass and density)- used to describe yield or biomass at a certain moment in time - Constant final yield refers to the relationship between total biomass and density at one point in time - it is not intended to describe changes through time - Relationship is described as: w = w(m) (1+ aN) ^-b - W: the mass of an individual plant - w(m) is max potential biomass per plant - a is the area a plant needs to reach max biomass - b is a parameter that produces constant final yield when b=1 - N = plant density - At any one moment in time , the graphs show that total biomass has a ceiling - If there is a ceiling on biomass, then when density is higher, plant sizes must be smaller - ****Self-thinning: the change in plant density and size through time , due to crowding (intraspecific competition) - Mortality falls most heavily on smaller plants - Self thinning trend is described by this equation - Log (w) = lo (c) - k log (N) - W: plant mass (weight) - C: a y-axis intercept - K: slope - N: surviving plant density - Generally, the slope (k) is roughly -4/3 until the population hits the yield ceiling, when the slope changes to -1 - Self thinning is sometimes called: the one true law of plant ecology - As plants get bigger , the trajectory line goes up to the left, and eventually the plants reach a size where the density and size hits the yield ceiling; after this, plants can only get bigger if some of them die - As plants get bigger and hit the biomass ceiling, density decreases because smaller plants die off - Size hierarchies - If one species is present, and K1 represents the carrying capacity, K1-N1 represents the unused carrying capacity (AKA tells us how much room the population has to grow) - When two species are present, K1-N1-aN2 represents “unused” carrying capacity - This is because you are finding the difference between the carrying capacity and the current population/impact - To determine “unused” carrying capacity, we needed to convert the numbers of species 2 into equivalents of species 1, thus the a - Zero-Growth Isoclines - Axes are the abundances of the two species - Isocline represents all of the possible combinations of numbers of the two species that result in a steady population (no increase/decrease)- AKA zero growth - Below line: population small below the carrying capacity, room for growth, so population would increase (right arrows) - Above line: over carrying capacity, so population would decrease (left horizontal arrows) - The point where the isocline comes close to touching the y axis (never actually touches) is where there are no species 1, and the amount of species 2 is determined by K1/a. - On the species 1 graph, arrows are horizontal because species 1 is represented on the x axis - On the species 2 graph, the arrows are vertical because species 2 is represented on the y axis - What happens when 2 species are present ? - When isoclines do NOT cross, then the species with the isocline on the outside will be the eventual winner at equilibrium- the community will go to the carrying capacity for that species, and the other species will be excluded - Above the yellow isocline, both species must decrease - The black arrows show the combined shift in populations; three of them also show the shift for each of species 1 and species 2 - What happens when you’re in between? - Species 2 must go down, but species 1 must increase - Species 2 will decrease until species 1 hits its carrying capacity, therefore showing the species with the most outside carrying capacity will always be the winner. - What happens when 2 species with isoclines cross - Can lead to stable coexistence of one species winning, depending on the positions of the isoclines and K values - The scenario will be short-term stable, but long term it will eventually go off balance and one will win - If the K’s are on the inside rather than the outside, the species can coexist. - Each species cannot become abundant enough to drive the other to extinction, so each species is limiting its own growth more than its limiting the growth of the other species. - ** The general principle is that species can coexist when intraspecific competition is more limiting than interspecific competition - Assumptions of the Lotka-Volterra model: - Overall, R* equilibrium models compare different levels of resources and populations to determine coexistence at equilibrium (long term) - Does not explicitly consider: - Spatial locations - Individual organisms - Herbivory - Disturbance - Resource dynamics are governed by renewal (resupply- the ability of the habitat to replenish resources that are used up) and consumption (organisms consuming a resource, making it less available for other species) - Population dynamics are governed by growth and mortality - L-shaped isoclines (R1 (ex. nitrogen) x axis, R2 (ex. phosphorous) y axis) - This is due to the fact that plant resources are not substitutable - R* gives perspective into resource levels and population numbers that occur at equilibrium - R* Theory: Assumptions: - In the absence of consumption, resources tend toward some habitat-specific maximum available levels; for two resources , these maxima define a supply point - The maximum resource level that the resource would return to without any consumption happening- supply point - Mortality is a fixed, habitat-specific constant for a given species - For plants, resources are essential (contrast to substitutable)- means isocline is L-shaped - Plants consume resources such that they are equally limited by both (or all) resources - Consume resources in ratios so they are limited by resources in equal amounts - Optimal foraging: plants should hunt for food in a way that maximizes amount of food for the amount of energy spent - Limiting resource is that which is in lowest supply relative to need - If resource levels are above the minimum required by a plant species, it’s population will increase until it reduces resource levels down to a point at which the population is at equilibrium - If a population grows, it will suck up resources and continue to grow until it hits the isocline - Plant resources are essential - Therefore, the isocline is a right angle - Dynamics of resources - (a) Renewal - if the location is not at equilibrium, resource levels will tend to move toward some equilibrium abundance - This tendency can be represented as a renewal vector (u), which always points towards the supply point no matter location on graph - Length of renewal vector represents the rate of resource renewal, and it is proportional to the graphical ‘distance’ from the supply point - Supply point is a characteristic of the habitat, not of the species, so is independent of the species present (note that field studies have not supported this assumption) - (b) Consumption - organisms consume resources, thus reducing them; this is represented by a consumption vector (c) - Optimal foraging theory predicts that a plant should consume two resources such that it is equally limited by both: parallel to diagonal line from the graph origin through the corner of that species’ isocline - Tilman - When two species consume resources, the effect is the sum of the two consumption vectors - The strength of consumption depends on how many plants there are - Dynamics of species’ populations - One species by itself - (a) mortality : assumed to be constant - The level of mortality in a given habitat, in combination with the species resource-growth curve, defines the resource level at which the population will be at equilibrium, the R* for that species and resource - Resource level on the graph where mortality crosses the growth curve - (b) growth : populations increase when resource levels are above R* for that species and resource, and decrease when resource levels are below R* - - Mortality helps define R* - - Dynamics of species’ populations - Two SPP, one resource : - - Equilibrium point is stable if, at equilibrium, each species consumes relatively more of the resource that limits it than of the resource that doesn’t limit it - Can happen if supply points are anywhere in zone 4- species can coexist- “zone of coexistence” - Introduces idea of resource partitioning - In other words, each species is most limited by different resource - - When two spp compete for two resources, the outcome is either sp A wins, sp B wins, or they coexist - Outcome depends on the location of the supply point relative to isoclines - Supply points in areas where both spp are limited by the same resource result in one sp excluding the other (winner is the one with the lowest R* for that resource) - Predictions of R* theory - In communities with: - Only one limiting resource - No herbivory or disturbance - Which go to equilibrium - This theory predicts that one species should exclude all other spp, resulting in a monoculture, or at least high dominance by one species (note similarity to classical competition theory) - r* theory should allow a priori prediction of which species will be dominant, and which species can coexist is: - Their R*’s for the limiting resources are known - The habitat’s supply point is known - If the R*’s are known, then the consequences (in terms of change in spp composition) of resource enrichment can be predicted - When there are two limiting resources in a homogenous community, this theory predicts the possibility of at most two species stably coexisting at equilibrium - Coexistence of more than two species on two resources is possible if there is heterogeneity of supply points at different locations - Does this fit with the competitive exclusions principle? R* is an example of niche differences that allow more than two species to coexist - This ONLY happens if we have enough supply points and supplies - Interspecific Competition pt. 3 - Competitive exclusion principle: identical competing species cannot coexist - Competitors can coexist if they have slightly different niches (niche differentiation) - Competition : a reduction in fitness due to shared use of a resource that is in limited supply - Effect : how much you alter the other species’ performance - Response : how much your performance is altered by the other species - Approaches to studying competition: - Competition experiments : done in greenhouses, in outdoor mesocosms, and in field experiments - Descriptive studies : document plant performance in relation to number, size, and distance to neighbors - One common way to quantify the intensity of competition is to create an index such as: - RCI = ( Perf(mono) - Perf(mix) ) / Perf(mono) - Perf(mono) is performance with only 1 species - Perf(mix) is performance with 2 or more species - Indices have a number of shortcomings - Greenhouse experiments have some limitations, including the “pot effect” - Plants are typically grown in pots, so may get too big - Field experts can have unintended consequences - Ex. watering attracts extra herbivory - In the centrifugal theory of community organization, core habitats are preferred by all species, probably because of optimal conditions like highly productive soils - Peripheral habitats are caused by stresses or disturbances- only some species have adapted to these conditions - Competition is intense in the core habitats but weak in peripheral habitats… poor competitors are excluded from the core habitats - Modern theory of coexistence - “Umbrella theory”- used to summarize a lot of theories - How can we explain coexistence - Chesson has summarized a modern theory of coexistence; it has two key features: - Fitness differences between species, also called “equalizing processes” - Niche differences between species, also called “stabilizing processes” (temperature, etc.) - If a lot of niche differences, species can coexist - If no niche differences, species cannot coexist - Niche differences are the traditional explanation for how species can coexist - Species can coexist if niche differences are very large, regardless of the amount of fitness differences - If niche differences are small, only a little fitness difference is enough to enable one species to exclude the other - Nonequilibrium ideas - R*, the triangle model, Lotka-Volterra, and the centrifugal theory are all ideas that focus on the equilibrium outcome of competition - Temporal fluctuations can result in species coexisting - What happens eventually when the community reaches a steady state - Non-equilibrium ideas focus less on the endpoint, and more on the “journey”... they assume things happen that prevent the community from frequently reaching an equilibrium - One important non-equilibrium idea is the lottery model - Temporal fluctuations can allow many species to coexist - The “paradox of the plankton” - Made famous by G. E. Hutchinson - He studied lakes in Connecticut and noticed that lots of plankton species seemed to coexist, yet they appeared to have approximately the same niches - Hutchinson proposed a non-equilibrium solution: - He said that as seasons change, the conditions in the lakes change (temperature, oxygen levels, light levels, etc.) - Each species of plankton could be a dominant competitor under particular environmental conditions, but they do not last very long - Under conditions ideal for a particular species, it would drive the others to extinction - But before that can happen, the conditions change and a different species is favored - Changing conditions prevent competition exclusion from forcing any species to extinction- thus many species can coexist - Lottery models (Sale- marine biologist studying species on coral reefs) - Lottery model works: where competition is for space; adults survive well once they possess a ‘spot’; and the spots appear unpredictably - Then the best strategy is to: be sedentary; produce MANY offspring; and disperse offspring widely - When multiple species using the above strategy are present in a habitat where competition is for space, and spots randomly open up, the offspring by default compete in a lottery - Each propagule is a lottery ticket: the propagules are assumed to be widely-dispersed; the draws occur when a spot opens up by the death of an adult - Which propagule gets the open spot is a random draw from among those propagules - The species with the most propagules will tend to get the most open spots, but the randomness of this process assures that even rare species will find spots occasionally - Although each species would eventually fluctuate to extinction, these circumstances allow coexistence of many species for a long period of time Herbivory - Individuals: - Extent : typically 10–15% of terrestrial productivity consumed by herbivores - Who ?: insects and mammals most important in terrestrial systems - Effects on individual plants depend on how much and which plant parts are consumed… may or may not cause death of the plant - Despite much discussion of overcompensation, herbivory most of the time is detrimental to plants- reducing growth and fitness - Overcompensation : the idea that plants actually grow more if they have been partially eaten - Plants grow more when they’re eaten - Today’s evidence does not support this - Populations - Although plant populations obviously are not always controlled by herbivory, there are dramatic examples, such as cases where vast tracts of forest trees have been killed by herbivorous insects: gypsy moths, spanworms, bark beetles - In some cases, these are introduced (exotic) insects, such as the hemlock wooly adelgid - The ghost in the lupine: Root herbivory by ghost moths - The sequence of influence from nematode to moth to lupine is a trophic cascade - Trophic cascade: organisms on one trophic level influence organisms two or more trophic levels away (higher or lower) - A common terrestrial trophic cascade is carnivores reducing the abundance of herbivores, which allows plants to increase - Hairston, Smith, and Slobodkin presented the “World is Green” hypothesis. They argued that in 3-trophic-level terrestrial communities - Argued based on the idea of logic - What controls population abundances at different trophic levels? - Producers (plants): competition - because the “world is green”, herbivores do not greatly regulate plants (Level 1) - Herbivores: predation - because they do not consume all of their food (plants), they must be kept in check by predation from higher trophic levels (Level 2) - Must not be competing with each other, so their abundances are kept in check by predation from the next higher trophic level - Carnivores: competition - because they don’t have predators above them, they must be regulated by competition (Level 3) - Detritivores: competition - because detritus does not accumulate and bury the world, detritivores must be regulated by competition - Starting from the top trophic level and working down, there is an alternative between populations being controlled by competition, then predation, then competition again - This is the World is Green hypothesis - Control goes from competition -> predation -> competition - Communities - The “world is green” hypothesis from HSS is a trophic cascade - Whether a trophic level is controlled by predation or competition is determined by the level above: plants, they are controlled by competition with each other because the herbivores are held to low levels by carnivores - How would things change if there was a fourth trophic level (ex. Second-level carnivores or hypercarnivores)? - Hypercarnivores controlled by competition; first-level carnivores controlled by predation… etc. would shift down scale - This is a top-down idea (opposed to a bottom-up idea, which would mean plant abundances are determined by abiotic factors) - Populations - Biological control has some spectacular successes and spectacular failures; its usefulness is still strongly debated, even though many agencies advocate for it - Prickly pear cactus and Cactoblastis moth in Australia - Moth introduced, and prickly pear cactus was lowered - Some biological control seems to work on purple loosestrife in wetlands of northeast and midwest, but not everywhere - Sometimes biological control agents switch to consuming native species… can have a very detrimental effect - A downside of this method - Terpenes - Toxic - Cardiac glycosides: affects heart - Monarch butterflies became immune - Caterpillars sequesters in tissues, so butterflies are toxic, and prevents bird from eating adult monarch - Can be constitutive (present at all times), or induced (absent at low concentrations until plant experiences herbivory) - Nicotine: induced - Cyanide: induced - Herbivory: communities: - Plant apparency - Herbivore diversity (number of herbivore species) that feed on a plant species is… - More on large plants than small plants - More on long-lived species than short lived species - More on widespread than localized plants - More on plants with close relatives than taxonomically isolated plants - Not much support Disturbance and Succession - Earliest work - Published in 1899 by Cowles - Studied dune vegetation along the shore of Lake Michigan - Cowles used a technique called chronosequence - Chronosequence : looks at different places to infer the vegetation at different times - Space-for-time substitution - Shortcomings - Assumes everyone started in same place - Climate same - Equal availability - Slow - Succession: a directional change in community composition and structure over time. - Typically more than one year - Begins with a disturbance - Secondary succession: happens on previously-vegetated land - Over time native and non-native species richness increases over decades - Primary succession: happens on land that has never been previously vegetated (rock) - Colonization of exposed surface following retreat of ice - Often takes hundreds to thousands of years because soil has to develop, which constrains rate of primary succession - A major limitation on rate of primary succession is that usually soil must develop along with vegetation - Diversity usually increases initially, but decreases in later stages - Relay floristics - Clements: dominant perspective until 1960; also called relay floristics - Considered plant communities to be tightly integrated groups of species whose temporal change was like the development of a superorganism - Predominant mechanism of change in species composition was facilitation, in which earlier species change environmental conditions in ways that are favorable for later species - Development was predictable, deterministic, and orderly; composition was determined by regional climate and therefore converged on a single endpoint even it starting with different compositions - Individualistic concept - Gleason: very early challenges to clements were the writings of Henry Gleason, who said that stochastic processes of dispersal and differential environmental tolerances determined community composition - Gleason argued that communities were simply collections of the species that happen to arrive and tolerate conditions; thus communities were not integrated and not analogous to organisms - Individualistic concept : Gleason’s concept of community organization did not predict orderly or deterministic change in species composition at various times/stages - Change occurs because the environment is altered by the plants, and the next species is whatever species happens to be able to tolerate the altered conditions and is present - Initial floristic composition - Egler : his idea was called initial floristic composition, and was sort of a “null model” for succession - He said that most of the species that eventually dominate in succession are present from the very beginning - Sequence of change was because some grow fast and some grow slow, so the slow growers become dominant later - Key point: the change was not caused by species interacting with each other, it was just due to inherent differences in growth rates - Types of interaction - An important milestone in thinking about succession was a paper by Connell and Slatyer in 1977, who suggested the interactions between species during succession fit into three categories - Facilitation : earlier species make it easier for later species to colonize and/or grow - Inhibition : earlier species inhibit colonization and growth of a later species - Tolerance : earlier species are neutral in respect to their effect on later species - Main causes of succession - Site availability - Disturbance - Resource gradients - Differential species availability - Seed dispersal - Seed bank - Survivors - Differential species performance - Life history - Physiology - Herbivory - Disturbance : a relatively discrete event in time that disrupts ecosystem, community or population structure and changes resource availability, substrate availability, or the physical environment - Can be classified on the basis of the legacies that remain after disturbances: - Really severe disturbances remove all organisms and organic materials, leaving a site with no legacies - Less severe disturbances leave some or most of the pre-disturbance organisms and/or organic material - Followed by secondary succession - Increased recognition of disturbance has led ecologists to abandon the notion of a climax community- an unchanging endpoint - Most now think of vegetation as in a dynamic equilibrium: usually changing at a small scale, but overall large scale composition rather steady - Characteristics of disturbances - Size: the area affected - Frequency: is how often a given disturbance affects a particular location - Severity: the actual impact or damage to vegetation - Intensity: is “how bad” the disturbing agent is - Disturbance sizes - Gaps in vegetation come in a wide range of sizes; larger gaps have more sunlight, higher air and soil temperatures, and require seeds of colonists to travel farther, compared to small gaps - Different species dominate in different-sized gaps: proportional contribution of intolerant/ruderal species should increase as gap size increases - The second way size of disturbance can influence what happens in succession is how it affects seed availability - Larger gaps require seeds to disperse farther, so center of large disturbed areas may be poorly colonized and therefore succession is slower - Fire disturbance - Wind disturbance - Both can be selective - Intermediate disturbance Hypothesis - Human activities have greatly increased deposition of various forms of nitrogen (ex. fertilizers), resulting in too much nitrogen - Eutrophication : nitrogen pollution in aquatic systems - Plants can use two forms of inorganic nitrogen: ammonium and nitrate - Nitrate (NO3-): very mobile in soil and soil water, and this has several consequences - It is easily leached out of soil, causing loss of nitrogen from the ecosystem - The leaching of nitrate can cause nitrogen eutrophication in streams and in lakes - Disturbances often reduce the uptake of nitrate and ammonium by plant roots (because the plants are killed), and this often allows much nitrate to be leached out of the ecosystems after a disturbance occurs - Ammonium (NH4+) is not very mobile, so may be less available to plant roots unless the ammonification happens immediately adjacent to the root - Decomposition : converts dead bodies, sloughed cells and tissues, urine and feces, etc. into soil organic matter - Soil organic matter is converted (in a process called mineralization ) into CO2 and inorganic nutrients - Most processes in decomposition require oxygen, so waterlogged soils or other anaerobic conditions cause organic matter to accumulate since decomposition is inhibited (Okefenokee Swamp) - Decomposition is slow in arid and nutrient-poor habitats - The biggest single component of what needs decomposing is plant litter - First stage (fragmentation) done by larger animals; true decomposition done by microfauna, fungi, and bacteria - Phosphorus cycle - Phosphorous is often very limited, and is immobile in the soil - Full phosphorus cycle is very slow because it includes ocean-bottom deposits forming into rock, and then geologic uplift to expose that rock in terrestrial environments - Main source of phosphorus for plants is weathering of phosphate-rich rocks- releases P into soil, where plants absorb it - Mycorrhizal fungi can be crucial to allowing plant roots to access phosphorus in soils- fungal hyphae can infiltrate tiny spaces in soil that plant roots cannot - Global Water Cycle - Potential Evapotranspiration (PET): the maximum possible transpiration if plant cover was 100%, and water unlimited - Actual evapotranspiration (AET): precipitation minus losses to runoff and percolation into deep groundwater - Deserts and grassland typically have evapotranspiration- precipitation, so a little runoff - Forests typically have precipitation -> evapotranspiration, so more runoff - The water cycle is not greatly influences by living things except by plants - Evapotranspiration can be very important to replenish the atmosphere, so less plants, less rainfall - Northern costa rica and southern nicaragua - Downwind cloud forest get less rain, which endangers the cloud forests - Carbon Storage (pools) - The largest carbon pools are in the rocks and deep sediments and in the ocean - There is a net movement of carbon from the atmosphere to plants/soil globally due to vegetation growth (counteracts deforestation) - Be familiar with relative sizes of the carbon pools - Gross primary productivity (GPP) : the total carbon fixed by producers (plants) - Hard to measure directly, so focus is more on NPP - Disturbances cause major upsets of the carbon cycle - Main fluxes are NPP (photosynthesis) and respiration - Respiration comes from roots, decomposing litter, dead wood, soil organisms, and aboveground plant parts - Distribution of carbon in forests - For the US, the largest pool is in the soil, followed by aboveground biomass of vegetation - All carbon pools in US forests have increased since 1990 - Globally, tropical forests store the most aboveground carbon - Boreal forests store the most belowground carbon - Disturbances have two types of effects: - They change the abiotic environment and ecosystem processes - They directly change the amount of carbon in various pools - Ex: wind - Disturbances immediately decrease the carbon stored in trees, and increases the amount of carbon stored in dead wood; not much effect on carbon in soils - Total carbon drops somewhat right after disturbance, but steadily increases after 10-20 years… eventually returns to pre-disturbance levels - Over decades, trees grow, increasing carbon in the tree pool - Over decades, dead wood decomposes, decreasing carbon in that pool - Currently, temperate forests are a carbon sink : they are absorbing a lot of carbon from the atmosphere… slowing the atmospheric carbon increase - This is the prediction that is most unique to the macarthur and wilson Equilibrium model - Large islands should support more species than small islands - Near islands should support more species than far islands - Island biogeography theory - The most famous test of the theory: Dan Simberloff did his dissertation at Harvard under E.O. Wilson- testing predictions of the equilibrium model - Several tiny mangrove islands in Florida Bay were reduced in size with a chainsaw. He then sampled the reduced islands after size reduction to test the area prediction - Species richness dropped on all “reduced” islands, even those “reduced” twice - Metapopulations - If we take some of the thinking from island biogeography theory and some thinking from out equation of population dynamics, we are close to the metapopulation concept - Sometimes populations exist as a bunch of islands with no mainland… so the sizes of populations nad how many islands they occupy is determined by local population dynamics plus immigration minus emigration - Metapopulation thinking can be extended to metacommunities if we assume that the species have similar migration and extinction probabilities - Theory makes predictions about the distribution of population sizes among the species in a community, and the frequency of occurrence of species among communities - An important insight that does hold is that populations can be classified as source or sink populations - Sink populations are always declining, but they get “rescued” by inputs from the source populations - Thus the population is never at equilibrium - SLOSS - The equilibrium theory of island biogeography theory has been very influential in conservation decisions: for example, reducing the size of a patch of habitat is predicted to reduce the number of species living there - SLOSS: Single large or several small - Should conservation try to preserve and protect one large block of habitat or multiple smaller blocks of habitat? - Arguments for several small are: - Possible spread of pathogens - Several small blocks might include a greater variety of habitats - Arguments for large blocks - Some species really do require conditions or resources only found in the interior of large patches - Fragmentation - One of the biggest conservation concerns for many types of habitats is fragmentation: breaking up larger stretches of intact habitat into smaller pieces - This may occur independently from loss of habitat area: you could have fragmented and unfragmented habitat that cover the same total area… although fragmentation often occurs along with loss of total area - Edge effects are differences between the outside perimeter of a patch and the interior - Corridors - “Bridges” that pass over highways for animals to cross - They allow the dispersal of organisms that cannot or will not cross the non-habitat - The dispersal can maintain species populations that might otherwise go extinct - Savannah River Corridor- found that organisms do use corridors Climate Change - Climate change is happening. - It’s not the sun - It’s not normal fluctuations - It is mostly because of greenhouse gasses (ex. Carbon dioxide), released by humans - The consequences are likely to be very serious (see next slide), although not “end of the world”. - “Denialists” are lying to you. - Possible consequences: - More severe weather (i.e. stronger hurricanes) - Rising sea levels & coastal flooding - Northward spread of tropical diseases - Massive extinctions - More acidic oceans - Longer & more damaging wildfire season - More severe draughts - Loss of mountain snowpack & glaciers – freshwater supply (example: 10 million in the area around Lima, Peru) - Reduced agricultural production - However, let’s be clear: nobody in the climate science community is predicting “the end of the world” – the denial camp wants to use this as a straw man. - The super-simple version - The greenhouse effect is caused by “greenhouse gasses” in the atmosphere: water vapor, carbon dioxide, methane, and others - Think of these gasses as a transparent blanket in the atmosphere - Some of the heat that would otherwise radiate out into space is trapped by the greenhouse gasses, causing the temperature to increase - Earth energy budget - - Let’s play ‘scientist’ - Let’s hypothesize about what we expect if the climate is warming : - Sea level should rise . - Ice caps, glaciers, permafrost should melt . - Species distribution should go up in elevation or go towards poles. - Timing of biological events (phenology) springtime is earlier - …and let’s hypothesize about what to expect if it’s a transparent blanket midway up in the atmosphere : - Heat escaping into space should decrease . - Heat reflecting back down to surface should increase . - Temperature IS increasing…globally. - Global average surface temperatures, monitored by three agencies: NASA (U.S.), NOAA (U.S.), and Hadley Center (U.K.). - 2016 and 2020 tied for hottest year, globally - How many of top 10 are in the last decade? All of them are within the last ten years - Warming is not the same everywhere - The Arctic is an area that has experienced some of the greatest warming. - Temperature is increasing in the U.S., Canada, China, Russia, & Australia - Oceans ARE warming- oceans have warmed over most of the globe - Don’t even need thermometers….. - It’s important to realize that a knock-out case for climate warming could be made without thermometers ! - Sea level IS rising. - In 2005, the IPCC developed scenarios of possible future carbon emissions, to use in climate models - Best case scenario was RCP 2.6 ; worst case scenario was RCP 8.5 - How are we doing? Scenarios - Recall that the RCPs were created in 2005. What have been the trends in emissions since then? Graph below shows that actual emissions through 2014 were on the same trendline as the most pessimistic RCP8.5 scenario... - And in 2021 and 2022 were slightly below the most pessimistic scenario - So… trends up to now would imply global warming of perhaps 2.5-4.5 degrees C by 2100 - Emissions Gap - In the 2015 Paris agreement, most nations pledged to take steps to keep warming below 2 ° C, and preferably below 1.5 ° C. - We know the levels of carbon emissions that must be reached by 2030 to fulfill these pledges. - The emissions gap is the difference between those necessary emissions levels, and the levels that current promises will yield. - Even our most optimistic promises are severely inadequate. - What are the projections? - Depending on the scenario, sea levels are projected to increase between 2 and 7 feet by 2100. - This will result in massive flooding of low-lying areas, such as Bangladesh. - If 18 million people are flooded out, where will they go? - Projected changes in number of days above 100˚ F, for southern Plains - The good news…. - While the outlook is very serious, it’s not hopeless….things you can do: - Reduce your electricity consumption. - GA Power is one of the dirtiest utilities in the country; pressure them to clean up. - Drive an electric or hybrid car. - Get some of your electricity from solar panels. - Vote for government leaders who are truthful, rational and forward-thinking. - Eat lower on the food chain. - Buy green! Climate Change pt 2 - Myths: - CO2 has little or no effect - Very prominent people in power tend to take this stance - Ex. Scott Pruitt, EPA administer in the Trump administration - The greenhouse effect of CO2 is not debatable - 1861, John Tyndall showed that if the amount of CO2 in a closed container increased, it retained more heat when a light was shown on it from above - You can demonstrate the absorption of heat by CO2 with two empty soda bottles, one filled with CO2, and one filled with air. Shine a bright light on the two bottles, the bottle filled with CO2 heats up more than the bottle filled with air - Based on this, all other things being equal, adding CO2 to the atmosphere must increase temperature - Over the last 800,000 years, CO2 and temperature have been directly correlated - There is no debate within the scientific community that in fact, the greenhouse effect from thousands and millions of years ago is what makes the Earth habitable- and that greenhouse effect is due to greenhouse gasses, so greenhouse gasses have an important effect - Dr. Richard Alley , a paleo-climatologist at Penn State, gave a lecture in 2009 called “ CO2- the biggest control knob ” - Climate has changed before - Reconstruction studies estimate pre-historic temperatures based on ice cores, tree rings, sediment cores, etc. - Ice cores trap ancient air - Tree ring patterns display tree growth in relation to temperature - Sediment cores reveal ancient ocean chemistry - Temperature histories from paleoclimate data compared to the history based on modern instruments suggest that global temperature is warmer now than it has been in the past 1,000 years, and possible longer - Temperature reconstructions tell us the Earth has not been this warm in the past 1500 years - In 2006 , the National Research Council summarized findings from six different labs that used independent methods and data to reconstruct past temperatures - They concluded that it is very likely that recent temperatures were greater than in the past 1000 yrs. - It is the sun - A common denier claim - There is no correlation between earth temperature and sun output in the last 40 years - There’s no consensus - Most nations have “national academies” of science; these are elite scientists of those countries; in the US National Academy, only 4 or 5 UGA faculty are members - In 2005, several national academies issued a joint statement affirming the mainstream climate change story - Signed by U.S., U.K., Russia, India, China, Canada, Brazil, France, Italy, Germany, and Japan - Doran and Kendall-Zimmerman surveyed more than 3000 earth scientists, more than 90% with PhDs. Among publishing climatologists , 97.4% agreed that humans are a primary cause of rising temperatures - In fact, seven different published studies examined the consensus on climate change, using either surveys of climate scientists, or the scientific journal articles related to climate - Global average surface air temperature anomalies, compared to 1951-1980 average - These are four of the most respected sources for global temperatures… and they are in remarkable agreement. Berkeley Earth is a research center established by people that did not believe in climate change - National Climate Assessments - 300 scientists contributed across 13 federal agencies - IPCC- Intergovernmental Panel on Climate Change: they issue periodic reports every 6-7 years - The most recent has been the 6th assessment; parts released in 2021 and 2022; final section due out in early 2023 - 831 authors from 80 nations; more than 2000 expert reviewers evaluated drafts - This is the most authoritative source for climate science - The models are wrong - Ross McKitrick is an economist at University of Guelph in Canada - His argument here is that CO2 has increased by 15% since the 1990’s but global temperatures have remained roughly at the 1900’s level - The models predict that as CO2 increases, the temperature should increase, therefore, the models are wrong - New study published in 2020 by Hausfather et. al compared predictions made for the 2004 IPCC report to observe global temperatures up through 2019 - The models used observed data up to 2000; years after 2000 were forecasts - Clearly, the models did a good job of predicting temperatures up through 2019 - The good air/bad air exchange with China - US Senate candidate Herschel Walker had this to say about climate change: - “Since we do not control the air our good air decided to float over to China’s bad air so when China gets our good air, their bad air got to move. So it moves over to out good air space. Then now we got to clean that back up.” - This is complete nonsense- nothing about this stance reflects reality