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Goal of the Lecture Lecture Structure FWF 410: “Populations and Communities” (Molles 2002 after Gause 1934) Matthew J. Gray, Ph.D. College of Agricultural Sciences and Natural Resources University of Tennessee-Knoxville Goal of the Lecture To familiarize students with biological organization terms, population distributions and growth, and basic concepts in community ecology. Reading Assignments: No Assigned Reading for Lecture Lecture Structure I. Levels of Biological Organization What is an individual, population and community? II. Population Distributions and Growth How are individuals distributed in space and how do populations fluctuate through time? III. Community Ecology What factors influence multiple species assemblages? 1 Levels of Biological Organization Individual: A living single or multi-celled organism. Population: A collection of individuals of the same species that have a some probability* of interaction and influence. Community: A collection of populations of different species that have a some probability of interaction and influence. Population Biology Introduction Study of the distribution and abundance of organisms. Terms Population: Group of individuals of the same species that have some probability to interact and reproduce (without dispersing). Distribution: The size, shape, and location of the area where a population exists. Abundance: Number of individuals in a population per unit time, Nt . 2 Density: Number of individuals per unit area (e.g., nt / m ) for a population. Why Study Populations? Populations provide an ecological entity of quantification for management & experiments. •Prudent human natural resource use (harvesting, non-consumptive use) Evolutionary •Human influences on organisms (disturbed vs. undisturbed) Unit Species of Conservation and Management Interest •Regulating mechanisms (competition, predation, habitat availability & quality) Distribution Patterns Scale & Pattern Types Scale Small: Area (e.g., <100 m) over which the environment does not change. “Home range” Large: Area (e.g., continent) over which the environment does change. “Sp. Dist.” Pattern 1) Random: All locations have equal probability (no biological interaction). 2) Regular: All locations have equal probability (‘−’ biological interaction or uniform resources). 3) Clumped: Locations have unequal probability (‘+’ biological interaction or clumped resources). Small Scale (1−3) Large Scale (#3) Important for Sampling Equal Antagonistic Clumped Design! P[loc] Interaction Resources 2 Population Growth Introduction Graphical behavior of population abundance over time. 2 Types: Plankton Blooms 1) Unlimited Population Growth: a) Geometric b) Exponential Rapid increase in population numbers due an abundance of resources typically at low population numbers. Adaptation: 1) Colonization of new habitats. 2) Exploitation of transient resources. 3) Recovery from population crash. 2) Limiting Population Growth: Logistic Growth Rapid increase in population numbers to a stabilizing, limiting abundance (K). Carrying Capacity (K): The maximum number of individuals that can be sustained in an environment at a given time. Abiotic ⇔ Biotic Factors A mathematical reality of all biological populations due to a decrease in available resources necessary for survival and reproduction. Survival + (by Age Class) Reproduction Rate of Population Change Survival Rate, lx: proportion of the population surviving to age x. Fecundity Rate, mx: average number of young produced per individual for age x. Net Reproductive Rate, R0: average number of young produced by an individual in its lifetime. n •R0 > 1 ⇒ Population Increasing •R ≅ 1 ⇒ Population Stable Rlm0 = ∑()xx 0 x=0 •R0 <1⇒ Population Decreasing Geometric Rate of Increase, λ: rate of change of the population trajectory. N = 25 Average Time 2 N t +1 Generation Time, T : e λ = from Offspring to N1 = 10 p t n lo S Offspring N t ∑ ()xlxx m x=0 25 T = λ ==25. R 10 0 Realized Rate of Increase, r : per capita rate of increase •r > 0 ⇒ Population Increasing ln()R0 (births−deaths) r = •r ≅ 0 ⇒ Population Stable T •r <0⇒ Population Decreasing Phlox Population Growth Many Geometric Growth Wildlife Non-overlapping Generations Conditions: Unlimited population growth by species that produce a single generation per year (i.e., 1 reproductive event thus population grows in DISCRETE annual pulses). Recall: N t +1 The abundance at t + 1 can be calculated using the λλ=⇔=NNtt+1 previous abundance & geometric rate of increase. N t m NNm = 1 λ Exponential Growth Overlapping Generations Conditions: Unlimited population growth by species that reproduce continuously (i.e., no discrete annual reproductive event thus population grows CONTINUOUSLY). Continuous population growth can be represented as a rate of change (i.e., derivative) where, r = realized rate of increase (avg. per capita increase) dN r = births − deaths (constant!) fN′()==rN Exp Growth Cannot dt Notice: as N increases, dN/dt increases be Sustained 3 Population Growth Logistic Growth Overlapping Generations K b = d Limiting Growth All populations ⇔ b−d= 0 are governed Sigmoidal ⇒ r= 0 •Food Availability by a limiting Curve +,∩ ⇒ Nt+1 = Nt •Space (competition) distribution & ⇒ dN / dt = 0 •Disease unable to grow K/2 •Parasitism •Predation without bound +,∪ ⎡ ⎛ N t ⎞⎤ NNrttm+1 =+−⎢11⎜ ⎟⎥ ⎝ K ⎠ indefinitely. discrete ⎣ ⎦ NOTE: K can fluctuate! Yeast Balanus African Buffalo Gause Connell Sinclair Waste Space Grass Limits to Population Growth Andrewartha What affects birth and death rates? Smith & & Birch Nicholson Environment vs. Organisms 1) Density-independent Factors: Food abundance Abiotic factors (e.g., precipitation, temperature) that can affect population growth. 2) Density-dependent Factors: Seeds/Caterpillars Biotic factors (e.g., competition, predation, disease) mx that can affect population growth. Galápagos Finches: El Niño Fledglings Rainfall vs. Nt 4X b > d 85% (starvation) b < d Community Ecology Introduction Study of the how abiotic and biotic factors affect the association and interaction of species in a given area. Community: An association of interacting species inhabiting some defined area. e.g., plant community, amphibian community, insect community Community Structure: The assemblage of a community, which includes: •Number of species (species richness) •Relative abundance per species (Nti, species abundance) •Types of species (composition) Guild: Groups of species exploiting a common resource in a similar fashion (i.e., have similar ecological roles). e.g., aquatic insect guilds Plant Shredders (CPOM) Grazers (algae) Complex assembly of component guilds. Life Collectors (FPOM) Predators Forms Why Study Guilds? 1) Focus on functional role 3) Manageable Unit 2) Focus on interaction 4) Basic Building Blocks 4 Species Diversity A combination of number of species and their relative abundance. Species Evenness Components: 1) Species Richness A measure (comparison) of abundance among 2) Species Abundance species. As abundance per species becomes “more even”, species diversity increases. A B Both have 5 species One species comprises 84% Each species comprises 20% and others 4% of community. of community. Common Misuse Species Diversity is Greater for Community B of Terms MAX() H′ = ln( SR ) Species Diversity H A′=−−(.0 662 ) MIN() H ′ = 0 Shannon-Wiener Index = 0. 662 A common method to calculate species diversity: s H ′=−∑ ppln H B′=−−(.1 610 ) th i i pi = proportion of the i species i=1 = 1610. Community A Species Abundance pi ln(pi)piln(pi) 1 21 21/25 = 0.84 ln(0.84)= −0.174 0.84(−0.174)=−0.146 2 1 0.04 −3.219 −0.129 3 1 0.04 −3.219 −0.129 4 1 0.04 −3.219 −0.129 5 1 0.04 −3.219 −0.129 25 −0.662 Community B Species Abundance pi ln(pi)piln(pi) 1 5 5/25 = 0.20 ln(0.20)= −1.609 0.20(−1.609)=−0.322 2 5 0.20 −1.069 −0.322 3 5 0.20 −1.609 −0.322 4 5 0.20 −1.609 −0.322 5 5 0.20 −1.609 −0.322 25 −1.610 Environmental Complexity In general, environmental complexity and species diversity are positively related. FHD and Bird Species Diversity FHD = foliage height diversity, where S = # of foliage layers & pi = biomass or volume per layer Robert MacArthur (1958): Examined niche partitioning of warblers in Maine. Found that number of pairs and warbler diversity increased with amount of vegetation and increasing FHD (increase in K and # of niches [unique habitats]). Volume of Foliage Foliage Height Diversity 5 Environmental Management Complexity Disturbance & Diversity Implications! Explains Part Intermediate Disturbance Hypothesis Equilibrium: A state when environmental conditions are more or less stable. Disturbance: 1) A state when environmental conditions are unstable. “Species Dependent” 2) Any discrete event in time that disrupts an ecosystem, community, “Ecology of Natural Disturbance” or population structure and changes resources, substrate availability, or the physical environment (White & Pickett, 1985). 26 Major Sources (fire, storms, disease, predation, human-induced) Hypothesis: Intermediate levels of disturbance (frequency & intensity) will result in the greatest species diversity. Too Much: Few species that complete life cycle between disturbance events. Too Little: Limited to most effective competitors (other excluded). Just Right: Sufficient time for a variety Science 199: of species to colonize & complete life 1302−1310 yet short enough to prevent exclusion. High Low Joseph Connell 6.
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