L34 2024 Ecology of Populations PDF

The Ecology of Populations Dominic McCafferty 1 2 Population ecology is the study of factors affecting the size of a population and how it changes over time 3 4 What defines a population? 5 Definit...

The Ecology of Populations Dominic McCafferty 1 2 Population ecology is the study of factors affecting the size of a population and how it changes over time 3 4 What defines a population? 5 Definition Group of individuals of a single species living in the same general area Described by their boundaries and size (number of individuals) Boundaries may be natural (a lake or island) or arbitrarily defined by an investigator (a county) https://ourworldindata.org/grapher/population-density?ti me=2024 6 Populations are members of the same species 7 Populations are defined by physical boundaries Burns NM, Hopkins CR, Quaggiotto MM, McCafferty DJ, Bailey DM (2022) Grey seal Halichoerus grypus breeding sites contribute substantial carrion biomass to the Firth of Forth. Mar Ecol Prog Ser 8 691:191-201. https://doi.org/10.3354/meps14053 Grey Seal population Habitat-based predictions of at-sea distribution for grey in British Isles and harbour seals in the British Isles. Sea Mammal Research Unit, University of St Andrews, Report to BEIS, OESEA-16-76/OESEA-17-78 9  10 https://nammco.no/grey-seal/ Individuals in populations interact Reproduce Compete for resources Intra-specific competition = competition for resources between members of the same population/species Inter-specific competition = competition for resources between members of different populations/species 11 Three important population concepts 1. populations have structure 2. population are regulated 3. populations are dynamic over time 12 Populations are structured 13 Population age and sex structure Population Pyramid age 14 Age related survivorship 15 Variation in mortality pattern - can be predicted from life-history strategy & environment Type I Mortality highest in older age classes Found in long lived species Living in a stable environment Iteroparous (reproduction spread throughout lifetime) https://www.earth.c om/ 16 Type II Mortality constant throughout life Found in short-medium lived species Living in a relatively stable environment Iteroparous (reproduction spread throughout lifetime) Belding’s ground squirrel 17  Type III High mortality in juveniles Short lived species Often semelparous* Unpredictable and temporary environments *Semelparous – reproduction in a single breeding event www.nature.scot 18  Survivorship Many species are intermediate to these curves or show more complex patterns For example, in birds, mortality is often high early in life (Type Ⅲ) but fairly constant among adults (Type Ⅱ) Survivorship curves can also differ among populations within a single species © Mark Pitt 19 Spatial structure of a population: dispersion is shaped by the ecology of a species Random Uniform Clumped 20 https://bio1110.nicerweb.com/Locked/media/ch08/distrib Random dispersion Position of each individual is independent of other individuals Occurs in the absence of strong competition or constant distribution of key physical or chemical factors 21  Uniform (regular) dispersion planted crops territorial animals 22 https://images.app.goo.gl/JGaCsjP2A77U1jRN9 Clumped dispersion Individuals aggregate in patches Aggregate in areas of high resource availability or favorable physical conditions Mating behavior and group predation or defense against predators can also influence https://images.app.goo.gl/yPYi19pN7K clumped dispersions ryAd8o7 23 Populations are regulated 24  Populations expand and contract Population growth = rate of change at each instant in time dN rN dN/dt change in dt r = per capita change in population size N at population size over short (instantaneous) each instant in time time intervals 25  Concept: Exponential Growth Exponential population growth occurs under ideal conditions; all individuals have access to abundant food and reproduce at physiological capacity Under such conditions, populations may increase in size by a constant proportion at each instant Elephant population in Kruger National Park, South Africa Equation of exponential population dN growth is: rN dt r is the intrinsic rate of increase, the per capita rate at which an exponentially growing population increases in size at each instant in time 27  But most populations do not grow exponentially…..The Logistic Growth Model In the logistic population growth model, the per capita rate of population growth approaches zero as the population size nears carrying capacity (K) The logistic model starts with the exponential model and adds an expression that reduces per capita rate of population growth as  K – N population size (N) increases dN rN  dt K 28 Figure 53.9  The Logistic Model and Real Populations Growth of laboratory populations of some small animals and microorganisms fit an S- shaped curve if resources are limited These populations are grown in a constant environment lacking predators and competitors 31  Some populations overshoot K before settling down to a relatively stable density if food becomes limiting, females may use energy reserves to continue reproducing; birth rates will decline when reserves are depleted Other populations fluctuate greatly and make it difficult to define K Density dependent regulation in the wild Grey seal Halichoerus grypus pup Aquatic Conservation, Volume: 29, Issue: S1, Pages: 6-23, First published: 06 September 2019, DOI: (10.1002/aqc.3134) 33 Density dependent factors 34 Density Independent factors https://isleofmaynnr.wordpress.com/2 020/02/09/storm-ciara/ 35 Current understanding of population regulation Both density dependent and density independent factors can operate Regulation differs between species In some species both have been shown to operate But must be some density dependent element or population will become extinct 36 Populations are dynamic 37 Population Dynamics https://images.app.goo.gl/i8rUJTaVaRP2HcWm8 38  Population cycles Barn owl Field vole https://www.mikerae.com/barn-owls-a-good -summer-and-better-future/ http://dx.doi.org/10.1098/rstb.2002.1118 39 Summary Population ecology is the study of factors affecting the size of a population and how it changes over time A population is a group of individuals of a single species living in the same general area and described by their boundaries and size (number of individuals) Most populations have structure are regulated dynamic over time 40 Reading Unit 8 Ecology of Life Chapter 53 Populations and Life History Traits Biology: a Global Approach, Global Edition (2020). Neil Campbell, Lisa Urry, Michael Cain, Steven Wasserman, Peter Minorsky, Jane Reece, and Rebecca Orr 12th Edition Pearson Education, Limited https://ebookcentral.proquest.com/lib/gla/detail.action?docID =6191695 41