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Lecture 3: Describing Populations

This lecture explores the unique characteristics of sessile organisms, particularly plants, including modular growth, phenotypic plasticity, and movements. It also discusses how plants disperse and the consequences of resting stages. The lecture further examines the demographic rates and life history strategies in populations, as well as the use of conceptual models and life tables.

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Lecture 3: Describing Populations

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  1. Lecture 3: Describing Populations FIRST, What are the unique characteristics of sessile organisms? ….Sessile?....

  2. How plants differ from (mobile) animals • Modular Growth • Importance of meristem tissue • Phenotypic Plasticity • Movements • How do plants disperse? Consequences? • Resting Stage • Ecological neighborhoods

  3. Modular Growth Clonal growth: ramet vs genet Semelparous vs Iteroparous

  4. Implications of Modular Growth • Loss of a part is not necessarily lethal • Reproductive output related to size • (also true of animals such as fishes) • Age of a genet may be very great • young ramets perpetuate the genet • If all meristems on all the ramets flower, • the genet dies:semelparous

  5. Phenotypic plasticity Definition Allows organisms to respond to local conditions Can lessen the effects of natural selection on the underlying genotype Examples….

  6. Movements- How do plants get around? -Seed dispersal • Often characterized by dispersal agent • abiotic vs. biotic transport • active vs. passive • Animals disperse seeds of 60-90% of • tropical plant species • Animals responsible for patchy occurrence • of plants

  7. Tapirs and Palms- an example Fragoso, Silvius, Correa. 2003. Ecol 84:1998-2006

  8. Resting stage- what are the consequences of reproduction by seeds? • How long do the seeds survive? • The seed bank- • implications for conservation and evolution • Dormancy may be broken by environmental • conditions or after some amount of time • has passed “DISPERSAL THROUGH TIME”

  9. Ecological Neighborhoods For plants…. For mobile animals… 2*STD of the mean dispersal distance during the organism’s reproductive lifetime

  10. REGARDLESS OF THE ORGANISM All populations may be described as the sum of four key processes: • Birth • Death • Immigration • Emigration N = B + I - D - E

  11. Demographic rates • Reproduction How many young are produced and recruit into the population? • Survival What is the probability of not dying in the current time interval? These processes are common to both plants and animals.

  12. Movement Dispersal- natal vs. post-breeding (adult) Issues…

  13. Closed Versus Open Populations Closed populations: • No immigration or emigration • Special case: no births or deaths Population is static: Membership is constant Most populations are not closed except for very short periods of time

  14. Life History Strategies Trade-offs between reproduction and survival Effects of size or age on reproduction and survival

  15. Type I Type II Log(survival) Type III Total lifespan Survivorship Curves (after Pearl 1927)

  16. A conceptual model: Model: abstract representation that includes only key features of system Conceptual models emphasize understanding over mechanistic explanation

  17. An idealized plant life cycle Time Adults Seedlings Seeds t t+1 Adults Seedlings Seeds Survival: Reproduction:

  18. Germination Survival Fecundity Growth Survival: Reproduction: An idealized plant life cycle Time Adults Seedlings Seeds t t+1 Adults Seeds Seedlings

  19. The components of N(t+1) N(t+1) = N(t) + B + I - D - E Ignoring I and E, and looking more closely at B and D N(t+1) = N(t) – N(t)*(1-S) + N(t)*F Death Birth A BOOK KEEPING PROBLEM!

  20. Life Tables • Life Tables summarize the survival and • reproduction of individuals according • to their age. Cohort life table Follow a group of individuals of the same age from birth through to when the last one dies Static life table Follow a group of individuals of mixed ages Over one year or less (a “snapshot” in time)

  21. n = 0 n = 1 n = 3 n = 5 age t = 1 t = 2 t = 3 t = 0 Diagram of a cohort study

  22. Diagram of a static study 3 n = 1 n = 2 2 age 1 n = 2 n = 3 0 t = 1 t = 2 t = 3 t = 0

  23. Problems with life table calculations • Static: assume that no’s individuals that are • born and that survive do not change • from year to year • Both types assume that all individuals • that are alive are counted • There are now much better ways to calculate • survival (mark-recapture, for example) • that do not depend on these assumptions

  24. Why are they still useful? Under some conditions, still can be used to calculate survivorship Still good for keeping track of individuals and vital rates for groups Historical perspectives

  25. SUMMARY “Plant” perspectives: modular growth phenotypic plasticity movement resting stages ecological neighborhoods The “BIDE” equation demographic rates plus movements Dispersal- types and issues

  26. SUMMARY continued Open versus closed populations Life history strategies: survivorship, reproduction Keeping track: conceptual models and life tables

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