Welcome back Happy 2011 Chapter 9 continued; Next chapters 10, 12, 13, and 14 Quiz 4 graded – mean: 76%; range: 45 % to 100% Next quizzes January 14 (9 and 10) January 19 (12 to 14) Your deadlines ? Make up classes Thursday January 13 – to 1.45 pm (Khoury 309) Thursday January 20 – – 1.45 pm (Khoury 309) 10/21/20151

Homework to all – on the web (1) How do I personally contribute to climate change? (examine your lifestyle — from your diet to your consumption to your home). Note: To answer this question, you should examine your ‘footprint.’ What is an ecological footprint. As explained by the Happy Planet Index, “[t]he ecological footprint of an individual is a measure of the amount of land required to provide for all their resource requirements plus the amount of vegetated land required to sequester (absorb) all their CO2 emissions and the CO2 emissions embodied in the products they consume. This figure is expressed in units of ‘global hectares’. The advantage of this approach is that it is possible to estimate the total amount of productive hectares available on the planet. Dividing this by the world’s total population, we can calculate a global per capita figure on the basis that everyone is entitled to the same amount of the planet’s natural resources.”Happy Planet Index So, to answer question (1), go to one The Global Footprint Network website ( and read the information they have, and then you can go to one of the following sites: The Ecological Footprint Quiz (here), or The Global Footprint Network (and assume we live in Turkey), or go to the website of the World Wildlife Fund and spend 5 minutes calculating the information (here) – but keep in mind that that calculation is designed for folks living in the UK so some of the questions won’t apply to you. There are other sites, of course. The links I provided are a selection of those sites. One other avenue you may use is an excel sheet to calculate your footprint with more accuracy and detail. Go here: Global Footprint Network website ( assume we live in Turkeyhere (2) What will I actually change in my behavior? (3) Assuming I have ultimate power in the world, what new world would I create? What is my vision for a healthier world — healthier from an environmental perspective, recognizing that the environment cannot be separated from the economy and from our philosophies. 2

Homework To all: “Me and Climate Change” Due January 17 To those of you who gave Homework 15 to 20% Summarize one peer-reviewed article from the scientific literature on the topic of ‘impact of climate change on…?’ The article must be NO older than Include the article with your summary. Due January 21 3

Top-down or bottom-up? Why is the world green? Is the world green because top-down control predominates green plant biomass accumulates because predators keep herbivores in check Or does the world taste bad? Even if the world is green (assuming it is), it does not necessarily follow that the herbivores are failing to capitalize on this because they are limited, top down, by their predators. Many plants have evolved defenses Herbivores may be competing and their predators may be competing World is bottom-up

Population and community structure and food web structure

Are there food web structures that are more stable than others? What is stability? A resilient vs a resistant community Resilient: returns rapidly to former state Resistant: little change A fragile vs a robust stability Fragile: remains unchanged but alters completely in large disturbance Robust: remains roughly the same in the face of larger disturbances Stability: in the face of disturbance Disturbance – loss of one or more populations from a community

Population and community stability Are there particular food webs that are more stable? [read box 9.5 to identify what ‘stable’ means] Stability: refers to stability in the face of disturbance or perturbation. What is a disturbance? In this case: loss of one or more populations from a community What are the effects of such a loss? A species that causes a significant effect (like what?) on at least one other species  strong interactor; keystone species 10/21/20157

Keystone species Removal of a keystone species  collapse of the structure  a community with different species composition Keystone species: “one whose impact is disproportionately large relative to its abundance” Can occur at ANY trophic level Lesser snow geese - herbivores that breed in large colonies in coastal marches; at nesting sites, adult geese grub fro roots and rhizomes of plants in dry areas  creating bare areas of peat and sediment  recovery of those areas is slow 10/21/20158

Conventional wisdom: increased complexity = increased stability But mathematical models do not support this argument Conclusions differ depending on whether we focus on individual populations within a community or on aggregate properties of the community (such as their biomass or productivity)

Food webs… 1.Number of species they contain 2.Connectance of the web (fraction of all possible pairs of species that interact directly with one another) 3.Average interaction strength between pairs of species Increases in # of species, increases in connectance, and increases in average interaction – all tend to decrease the tendency of individual populations within the community to return to their former state following a disturbance (resilience) Thus – community complexity leads to population instability

What is found in real communities – and not in models? Keep in mind that: The only communities we can observe are those that are stable enough to exist Data on interaction strength for whole communities are unavailable – so assume contant Recent studies: Connectance may decrease with species number …or… May be independent of species number … or … May even increase with species number Conclusion? Stability argument does not receive consistent support from food web analyses either

Summary of this chapter there are multiple determinants of the dynamics of populations Dispersal, patches and metapopulation: movement can be vital factor in determining and/or regulating number There are temporal patterns in community composition No predator-prey, parasite-host or grazer- plant pair exists in isolation

Chapter 10

-- review -- Every population exists within a web of interactions with other populations across several trophic levels Each population must be viewed in the context of the whole community Populations occur in patchy and inconstant environments in which disturbance and local extinction may be common 14

…to add… Need to appreciate that the world’s biological diversity is becoming increasingly important Need to understand why species richness varies widely across the face of the Earth Why do some communities contain more species than others? Are there patterns or gradients in biodiversity? If so, why? 15

Species richness… The number of species in a community Why is it difficult to count or list the species in a community? Taxonomic inadequacies Only a proportion of the organisms can usually be counted Number of species recorded… Depends on the number of samples that have been taken or on the volume of the habitat that has been explored But…the most common species are likely to be represented in the first few samples… more samples -> rarer species will be added ? – at what point does one stop taking further samples? Until the number of species reaches a plateau Species richness of different communities should be compared only if They are based on the same sample sizes Area of habitat explored Time devoted to sampling Number of individuals included in the samples 16

Diversity indices Species richness two communities with ten species…but Diversity indices Combines both species richness and evenness or equitability of the distribution of individuals among those species Calculated by determining for each species, the proportion of individuals or biomass that that species contributes to the total in the sample Diversity then increases with equitability, and for given equitability, diversity increases with species richness 17

18

Add to those factors… (1) interspecific competition If a community is dominated by interspecific competition, the resources are likely to be fully exploited Species richness will then depend on the range of available resources (specialists and niche overlap) (2) predation Exerts contrasting effects Predators can exclude certain prey species  community can be less than fully saturated (unexploited resources)  predation may reduce species richness Or predation may keep species below k – reducing intensity and importance of competition for resources  more niche overlap and a greater richness of species 19

…and other factors… Factors that vary spatially Productivity Predation intensity Spatial heterogeneity Environmental ‘harshness’ Factors that vary with time (temporal variation) Climatic variation Disturbance Evolutionary age 20

Spatially varying factors Productivity and resource richness For plants: productivity of the environment can depend on most limiting element (nutrient or condition) Animals: broadly speaking, productivity of environment for animals follows the same trends as for plants Why? Due to changes in resource levels at the base of the food chain 21

Productivity and richness Expect species richness to increase with productivity Supported by an analysis of species richness of trees in North America in relation to a measure of available environmental energy, potential evapotranspiration (PET) Amount of water that under prevailing conditions would evaporate or be transpired under a saturated surface Water and energy Energy: heat and light Higher energy inputs lead to more ET and more water Southern African trees – species richness increased with water availability (annual rainfall) but first increased and then decreased with available energy What about animals? Animal species richness positively correlated with crude atmospheric energy 22

23

Productivity and species richness Why? Not sure… but For an ectotherm (eg – a reptile) – extra atmospheric warmth  increase intake and use of food resources For an endotherm (eg – bird) – extra warmth  less use of resources in maintaining body temp and more resources for growth and reproduction In both cases  faster individual and population growth  larger populations Warmer environments might -> allow species with narrower niches to persist and such environments may support species 24

Productivity and species richness May also be a direct relationship between animal species richness and plant productivity 25

Strong positive correlations between species richness and precipitation for both seed-eating ants and seed-eating rodents; more species of very large ants and very small ants. Why? Species richness of fish also increases with lake’s phytoplankton productivity Note: increase in production does not always lead to increase in diversity 26

Predation intensity Predation may increase richness By allowing competitively inferior species to coexist with their superiors (predator-mediated coexistence) Predation may reduce richness Intense predation may drive prey species to extinction Overall: predation intensity and species richness: humped relationship Greatest richness at intermediate intensities 27

Removed starfish from an 8 m long and 2 m deep shoreline Other species became dominant (barnacles and then mussels) Later – reduction in species richness Predator- mediated coexistence 28

Wolves… The gray wolf was reintroduced to Yellowstone National Park in the spring of 1995, after a 70-year absence. In the past 6 years, the population has grown from 31 released animals to more than 100 individuals, as wolves have exploited an abundant elk population. Consequently, elk that had previously experienced significant mortality primarily in the late winter because of starvation now face mortality throughout the year. When an elk is killed by wolves, its carcass is partially consumed by the wolves and then is scavenged extensively by eight other carnivore species (coyote, bald eagle, golden eagle, grizzly bear, black bear, raven, magpie, and red fox) and less intensely by up to 20 other species. Field observations indicate that the infusion of wolf-killed ungulate carrion throughout the year has created an abundant and dependable food source for these other carnivores. 29

Spatial heterogeneity Environments – more heterogeneous – more potential for species richness. Why? Some studies: positive relationship between plant diversity and heterogeneity Substrate…slope… drainage … soil pH Most studies: related species richness of animals to structural diversity of plants in their environment Due to experimental manipulation of plants Or through comparisons of natural communities that differ in plant structural diversity Or plant species richness 30

Environmental harshness Environments dominated by extreme abiotic factor (harsh environments) more difficult to recognize than apparent Anthropocentric view. What is cold for us might seem benign to a penguin ‘let the organism decide’ harshness factor Environment extreme – if organisms, by their failure to live there, show it to be so. Circular definition. Environment extreme: one that requires, of any organism tolerating it, a morphological structure or biochemical mechanism that is not found in most related species and is costly, either in energetic terms or in terms of the compensatory changes in the biological processes of the organism that are needed to accommodate it Example: plants living in highly acidic soil (low pH). Need specific structures/mechanisms Harsh environments: low species richness Hot springs. Caves. Highly saline water (Dead Sea) Each also categorized by low productivity and low spatial heterogenity 31

Temporally varying factors Climatic variation Is the variation predictable? (relative time scales) … temporal niche differentiation Opportunities for specialization in a non-seasonal environment Is the variation unpredictable? – climatic instability Could increase species richness …or not Does species richness increase as climatic variation decreases? Disturbance Environmental age: evolutionary time 32

33

Temporally varying factors Disturbance Reminder: In a dominance-controlled community  community succession Very frequent disturbances: keep most patches in early stages of succession (few species) + rare disturbances allow patches to be dominated by best competitors (few species) Conclusion: intermediate disturbance hypothesis All communities are subject to disturbances that exhibit different frequencies and intensities Environmental age: evolutionary time 34

Temporally varying factors Environmental age: evolutionary time Communities may differ in species richness because some are closer to equilibrium and therefore more saturated than others Some argued that tropics are richer than temperate in part because tropics have existed over long and uninterrupted periods of evolutionary time (temperate regions – recovering from glaciations) But tropical areas were also disturbed during the ice ages by associated climatic changes that saw tropic forest limited to a small number surrounded by grassland Another explanation: species evolve faster in the tropics because of higher rates of mutation in these warmer climes Rates of evolution of woody plant species twice as fast in the tropical species 35

Gradients of species richness Habitat area and remoteness: Island biogeography Latitudinal gradients Gradients with altitude and depth Gradients during community succession 36

Island biogeography Number of species on islands decreases as island area decreases. Species-area relationship What is an island? Islands of land in a sea of water Lakes - Islands in a sea of land Mountaintops – high altitude islands in a low altitude ocean Gaps in a forest canopy – island in a sea of trees Islands of particular geological types, soil types, or vegetation types 37

Start here Island biogeography Species-area relationships: one of the most consistent of all ecological patterns Is the impoverishment of species on islands more than would be expected in comparably small areas of mainland? Why do larger areas contain more species? Encompass more different types of habitat – not enough of an explanation Island size and isolation: number of species on an island determined by a balance between immigration and extinction; this balance is dynamic; and extinction rates may vary with island size and isolation 38

Island biogeography 1.The number of species on an island should eventually become roughly constant through time 2.This should be a result of continual turnover of species, with some becoming extinct and others immigrating 3.Large islands should support more species than small islands 4.Species number should decline with the increasing remoteness of an island - MacArthur and Wilson’s theory’s predictions 39

Latitudinal gradients Increase in species richness from the poles to the tropics Why? No clear explanation. Latitudinal gradient intertwines components previously discussed… 40

Gradients with altitude and depth Decrease in species richness with altitude – akin to that observed with latitude - -in terrestrial environments Other studies: increase with altitude; other studies: hump-shaped patterns Productivity and temperature? Productivity and growing season? Stress with extremes? In aquatic environments: change in species richness with depth strongly similar to terrestrial gradient with altitude 41

Skip – patterns in taxon richness in the fossil record 42

Summary Richness and diversity Productivity and resource diversity Predation intensity Spatial heterogeneity Environmental harshness Climatic variation Disturbance Environmental age Island biogeography Gradients in species richness 43