BIOB50H3F Ecology Fall 2024 Lecture Notes PDF

BIOB50H3F Ecology Fall 2024, Week 11 Communities Through Time From Individuals to Populations to Communities and Ecosystems Lecture 3 Lectures 9-11 Individual...

BIOB50H3F Ecology Fall 2024, Week 11 Communities Through Time From Individuals to Populations to Communities and Ecosystems Lecture 3 Lectures 9-11 Individual Community (an association of interacting populations of different species, living and Lectures 4-5 interacting in the same area) Population (group of individuals of same species, living and interacting with one another in a particular area) Ecosystem (a community of organisms plus their abiotic (physical) environment) NATURE IS DYNAMIC Nature is Dynamic The “Balance of Nature” Before Darwin’s work, nature was typically viewed to be “in balance”, where each species “plays its part” to maintain a stable ecosystem, and where ecosystems always return to a “natural state” after a small disturbance – a view that persists in popular culture until today. e.g., Herodotus, ~484-425 BC: predators never excessively consume prey populations to maintain a “wonderful balance” Everything is changing. All the time. Nature is dynamic. Change is the rule, rather than the exception. Example: seasonality Everything is changing. All the time. Nature is dynamic. Change is the rule, rather than the exception. Example: altered animal home ranges during the COVID-19 pandemic Everything is changing. All the time. Nature is dynamic. Change is the rule, rather than the exception. Example: (some of the) wildfires in Brazil (2019), Australia (2020), California (2022), and Canada (2023) Everything is changing. All the time. Nature is dynamic. Change is the rule, rather than the exception. Example: ecological succession Everything is changing. All the time. Nature is dynamic. Change is the rule, rather than the exception. Example: six species mass extinctions Everything is changing. All the time. Yet, predictable patterns emerge across spatial and temporal scales all the time. How is that possible? SUCCESSION Succession Communities change in fairly predictable ways. Ecological succession is the series of changes in the species composition of a community through time at a particular location that occur in a fairly predictable way as a result of biotic and abiotic influences, as the location goes from bare rock or lifeless water to being filled with interacting species. Succession Primary vs Secondary Succession Primary succession refers to succession that begins in/on substrates that contain no organisms and no organic material. Primary succession tends to be slow, as the first colonists must arrive from elsewhere, and it is only through the actions of these species that the environment becomes suitable for the establishment of species in later seres. Succession Primary vs Secondary Succession The frequency and intensity of disturbance determines to which stage a community is set back, and thus, whether primary or secondary succession occurs. Succession Primary vs Secondary Succession Secondary succession occurs following a disturbance where some, but not all, organisms have been destroyed. Succession Life History and Succession Early successional species tend to be r-selected; late successional species tend to be K-selected. Succession Life History and Succession Early successional species tend to be r-selected; late successional species tend to be K-selected. Succession Example: Primary Succession on Mount St. Helens Mt. St. Helens Eruption May 18, 1980 https://www.youtube.com/watch?v=-H_HZVY1tT4 Mount St Helens Time Lapse From Space, 1979-2009 https://www.youtube.com/watch?v=R3R0eQOWmPE Succession Example: Primary Succession on Mount St. Helens Succession Example: Primary Succession on Mount St. Helens Succession Example: Secondary Succession in North Carolina’s Piedmont Forests Succession Example: Animal Succession in North Carolina’s Piedmont Forests Example: Shifts in the bird community of North Carolina’s Piedmont Forests over time are associated with successional plant community changes and differing habitat preferences among bird species Succession Example: Tommy Thompson Park, Toronto Succession General Patterns Succession relies on complex sets of biotic interactions Primary succession takes longer than secondary succession Plant cover, biomass, species richness, and species diversity all tend to increase over time Chance events play a significant role in determining successional pathways Succession Conceptual Models of Succession: Connell & Slayter’s Facilitation, Inhibition, and Tolerance Models of Succession Facilitation model: Early species modify the environment in ways that benefit later species. The sequence of species facilitations leads to a climax community. Tolerance model: Early species modify the environment in ways that neither benefit nor inhibit later species. Inhibition model: Early species modify the environment in negative ways that hinder later successional species. Succession requires disturbance for succession to continue. Succession Conceptual Models of Succession: Connell & Slayter’s Facilitation, Inhibition, and Tolerance Models of Succession To test which mechanisms are determining the observed successional pathways, a field experiment was conducted: add spruce seeds to each successional stage, and monitor their rates of germination, growth, and survival over time. Both facilitative and inhibitory effects on spruce seedlings. But direction and strength of effects varies with successional stage. ~ facilitation model ~ inhibition ~ tolerance model model Succession Conceptual Models of Succession: Connell & Slayter’s Facilitation, Inhibition, and Tolerance Models of Succession Many experimental studies show that succession is driven by a variety of mechanisms that all interact. Typically, none of Connell & Slayter’s succession models is able to explain successional changes throughout all stages; rather, different models seem to explain different parts of the successional path. Bigger, long-lived Facilitation likely Mixture of positive species; competition most important, and negative most important especially when interactions physical conditions are stressful Late succession Mid succession Early succession COMMUNITY ASSEMBLY Community Assembly While large-scale patterns of community succession can be fairly predictable, different communities will have different species compositions. Community assembly may vary, for example, because of priority effects. Example: Cuckoo-doves in New Guinea Community Assembly Assembly Rules Assembly “rules” are guiding principles outlining how the timing of species arrival or the initial suite of colonizing species can determine the species composition of the community. At least some such rules must exist (e.g., obligate parasites cannot establish without their host; specialist predators cannot establish without their prey; obligate mutualist cannot establish without their mutualistic partner),… Lecture 1 Community Assembly Assembly Rules Assembly “rules” are guiding principles outlining how the timing of species arrival or the initial suite of colonizing species can determine the species composition of the community. At least some such rules must exist (e.g., obligate parasites cannot establish without their host; specialist predators cannot establish without their prey; obligate mutualist cannot establish without their mutualistic partner),… but general rules are difficult to establish empirically due to the many possibilities that a community can assemble: there are typically many more possible combinations of species assembly than there are communities, making it difficult to demonstrate that observed patterns of species co-occurrence are nonrandom. Community Assembly Assembly Rules: James Drakes’ Experiments Assembly rules can be studied in experimental microcosms. Community Assembly Assembly Rules: James Drakes’ Experiments Assembly rules can be studied in experimental microcosms. James Drakes’ experiments showed that: - widely differing community compositions can be achieved by solely altering the sequence of colonization - variability among replicates was low, suggesting repeatable mechanisms at play - some sequences can lead to community compositions that prevent any further colonization Community Assembly Restoration Ecology Restoration ecology provides many large-scale “experiments” on community succession and applies successional principles for management. It aims to manage highly degraded or newly established sites by providing conditions that make sites physiologically tolerable for a diverse array of species to accelerate succession towards a desired endpoint community. Example: Sacramento River National Wildlife Refuge, Example: Tommy Thompson Park, Toronto (succession California (succession on abandoned farmlands) on newly established landfills) DISTURBANCE DYNAMICS Disturbance Dynamics Disturbance Humans are responsible for many disturbance events, but disturbance is also an integral and natural part of all ecosystems. Example, Human-Caused Disturbance: Oil spill Example, Natural Disturbance: Hurricane Disturbance Dynamics Disturbance Disturbance is an integral part of all ecological systems. Depending on type, frequency, and intensity, disturbance may reset successional processes, or enable then. Example: forest fire might reduce the abundance of dominant species and facilitate the colonization Example: lava flow removing success of other species (nearly) all living matter, leading to primary succession Disturbance Dynamics Disturbance Definitions of disturbance may vary based on the context, ecosystem, and research question, but are generally understood to refer to some type of event that disrupts ecological processes and/or ecosystem, community, or population structure, and which directly or indirectly creates opportunities for new individuals to be established. Example, Abiotic Disturbance: Hurricane Example, Biotic Disturbance: Grasshopper outbreak Disturbance Dynamics Example: The Effects of Human Disturbance on Mammalian Communities on the Osa Peninsula, Costa Rica Disturbance Dynamics Example: The Effects of Human Disturbance on Mammalian Communities on the Osa Peninsula, Costa Rica Disturbance Dynamics Example: The Effects of Human Disturbance on Mammalian Communities on the Osa Peninsula, Costa Rica Disturbance Dynamics Example: The Effects of Human Disturbance on Mammalian Communities on the Osa Peninsula, Costa Rica Disturbance Dynamics Example: The Effects of Human Disturbance on Mammalian Communities on the Osa Peninsula, Costa Rica Disturbance Dynamics Types of Disturbance Many types of disturbance exist, making it difficult to generalize how disturbance affects ecosystems, communities, and populations. Disturbance Dynamics Intermediate Disturbance Hypothesis Many types of disturbance exist, making it difficult to generalize how disturbance affects ecosystems, communities, and populations. One important generalization that has been proposed in the 1970s is the intermediate disturbance hypothesis. It suggests that species diversity will be greatest at intermediate levels of disturbance a stable environment leads to competitive exclusion by dominant species for many other species and limits diversity (mostly high mortality through K-selected species disturbance excludes will persist) many species and limits diversity (mostly r- selected species will persist) Disturbance Dynamics Intermediate Disturbance Hypothesis The intermediate disturbance hypothesis has been fairly successful in explaining species diversity in some well- understood systems, but when viewed across hundreds of studies, diversity peaks at intermediate disturbance values in only a minority (~20%) of studies. Example: vegetation growth on boulders in the intertidal zone ALTERNATIVE STABLE STATES Alternative Stable States Although succession and other ecological dynamics often follow predictable pathways, … …, disturbances can affect which path is taken. Lecture 9 Alternative Stable States Equilibria Recall: A system is at equilibrium if its rate of change is zero. A system may have more than one equilibrium. Lecture 7 Alternative Stable States Stability Recall: A system is at equilibrium if its rate of change is zero. A system may have more than one equilibrium. Equilibria may be stable or unstable unstable equilibrium stable equilibrium Lecture 7 Example: Equilibria of population growth models Alternative Stable States Stability Recall: A system is at equilibrium if its rate of change is zero. A system may have more than one equilibrium. Equilibria may be stable or unstable unstable equilibrium stable equilibrium Lecture 6 Example: Equilibria in the Lotka-Volterra model of competition Alternative Stable States Stability Recall: A system is at equilibrium if its rate of change is zero. A system may have more than one equilibrium. Equilibria may be stable or unstable unstable equilibrium stable equilibrium Lecture 7 Example: Equilibria in the Lotka-Volterra model of predation Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium to another than the other way round. unstable equilibrium stable equilibrium Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium into another than the other way round. Lecture 7 Example: Equilibria of population growth models with an without an Allee effect. Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium into another than the other way round. Lecture 7 Example: Equilibria in the Lotka-Volterra model of competition Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium into another than the other way round. Lecture 1 Example: Trophic cascades due to overfishing Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium into another than the other way round. Lecture 9 Example: Eutrophication due to overfertilization Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium into another than the other way round. Example: Coral bleaching due to climate change and ocean acidification Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium into another than the other way round. Example: Coexistence and alternative stable states in the bioeconomics of fisheries and aquaculture Alternative Stable States Bistability A system may have one or more stable equilibria. We refer to a system as bistable if there are two different stable equilibria to which the system can be attracted. Hysteresis occurs when a larger perturbation is needed to shift the system from one stable equilibrium into another than the other way round. Example: Coexistence and alternative stable states in the bioeconomics of fisheries and aquaculture  Think – Pair – Share With polar bears potentially going extinct in several regions of the Arctic, how do you think Arctic marine communities and food webs will change over the next century?  ASSIGNED READINGS: Chapter 13 (excluding Figs. 13.20 & 13.21) Please note: Quiz 10 covers lectures 10 and 11, and is due on Nov 26.