Start today, no lecture on Friday (April

24th) finish on Monday.

CHAPTER 18 – POPULATIONS, SELECT BITS FROM 19

Populations – group of individuals of one species living in a discrete area Species?

Multiple concepts, Biological Species Concept the most handy

Populations of multiple species together make up a community More in upcoming chapter

Speciation will make more species, need to keep new species separated

POPULATIONS

Allopatric speciation Speciation in geographic isolation

Sympatric speciation Speciation while still near each other Tougher, but sexual selection and strict assortative mating

by morph may be a key

Speciation has occurred and 2+ good species exist if no hybridization can occur and species stay separate Pre- and post-zygotic barriers reinforce

POPULATIONS

Populations of birds (all species actually) are dynamic Both short-term and long-term Has impacts on genetic variability

Changes in environment can impact populations, sometimes severely

Typically, a healthy population can rebound from decreases

POPULATIONS

POPULATIONS

Great Tit (Parus major) populations show overall increases but yearly fluctuations in British forests

POPULATIONS

Here overall patterns of Northern Bobwhite Quail (Colinus virginianus) and Scaled Quail (Callipepla squamata) show decreases in population size, probably due to habitat loss and over-hunting

Bird populations can have great growth European Starlings (Sturnus vulgaris) House Finches (Carpodacus mexicanus)

Short generation time important to growth Large numbers of offspring at each attempt General food requirements General nesting requirements Pugnacious behavior

Eventually populations hit their carrying capacity What the environment can support

This can vary!

POPULATIONS

POPULATIONSCattle Egret (Bubulcus ibis)

POPULATIONS

What allows populations to grow? Recruitment of new

individuals Young returning to natal

area after migration Young (non-migrants)

remaining in natal area Young from neighboring

populations moving in Adults from neighboring

populations This often called

immigration

Juvenile Eastern Bluebird (Sialia sialis)

POPULATIONS

More work with the Great Tit

One thing to remember there are differences between limitation and regulation of populations, although they are associated

Limitations Habitat – need the appropriate habitat to

breed/forage/survive Red-cockaded Woodpeckers (Picoides borealis)

Food – need food to keep the metabolic machinery going Influential to year-to-year fluctuations

Northern owl species movements in 2005 Natural enemies – predators and parasites

Typically predators and parasites don’t limit/regulate, but sometimes strange things happen

Diseases and human movement of them is particularly scary now

POPULATIONS

POPULATIONS

Here we see densities of Great Tit pairs breeding in different quality habitat (A is best, C is worst).

Habitat quality/quantity is particularly impactful to migrating species.

POPULATIONS

Here changes in food availability drive population size changes in 4 seed-eating finch species (these counts are in the US from Christmas bird counts, 1969 counts are unusually high)

POPULATIONS

Predators that have been introduced can be of severe impact Feral cats – most

successful of predators Rats – successful

predators (nests) Brown Tree Snakes Humans – we will eat

stuff till it’s gone

Feral cats are perhaps the most successful predator/mammalian migrant known

POPULATIONS

Diseases can also be particularly devastating New diseases that

current bird populations do not have good resistance to Avian malaria in

Hawaiian Islands Limited genetic

variability in host means poor resistance

Here a House Finch has an infection of Mycoplasma gallisepticum, limited genetic variation in Eastern US populations led to great susceptability and death of infected individuals

POPULATIONS

Parasitic blowflies are dangerous to nestlings and these have been moved into new areas due to human activities

POPULATIONS

West Nile Virus is a relatively newer threat, some species are highly susceptible to it while others are not bothered that much. Here impacts on American Crows (Corvus brachyrhynchos) are detrimental while Northern Cardinals (Cardinalis cardinalis) seem to be unaffected

Regulation Social factors – many individuals want limited resources, this

becomes a limiting situation

POPULATIONS

POPULATIONS

Black-throated Blue Warbler (Dendroica caerulescens), female at top, male at bottom

POPULATIONS

Here social factors in Red Grouse (Lagopus lagopus scotica) influence population trends

Pay attention only to the solid line with connecting dots, the others are specific to the paper which I cannot get

Long-term population trendsThese data must come from larger sources

Long-term research Examples given in book Dark-eyed Junco (Junco hyemalis)

Christmas Bird Counts – growing in popularity Breeding Bird Surveys

Changes in populations that are tracked over time can give information on the health of the population and environment

POPULATIONS

POPULATIONSPOPULATIONS

Changes in Bald Eagle (Haliaeetus leucocephalus) populations indicated something was wrong, with ban on DDT populations began to rebound

POPULATIONS

Populations can crash or hit bottlenecks Human interference Natural occurrences

Leads to reduced genetic diversity Few survivors and may

not be representative

Small populations (e.g., island species) at particular peril Mauritius Kestrel (Falco punctatus), once the

most endangered bird ever, now has rebounded due to intervention by Carl Jones