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

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

Modular Growth Semelparous vs Iteroparous Clonal growth: ramet vs genet

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

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

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

Tapirs and Palms- an example Fragoso, Silvius, Correa Ecol 84:

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

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

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

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

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

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

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

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

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

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

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

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 BirthDeath A BOOK KEEPING PROBLEM!

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)

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

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

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

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

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

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