Exploring Populations Dynamics: Species, Growth, and Regulation

1. Chapter 18 – Populations, select bits from 19 Start today, no lecture on Friday (April 24th) finish on Monday.

2. Populations • 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

3. 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

4. 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

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

6. 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

7. Populations • Bird populations can have great growth • European Starlings (Sturnus vulgaris) • House Finches (Carpodacusmexicanus) • 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!

8. Populations Cattle Egret (Bubulcus ibis)

9. 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)

10. Populations More work with the Great Tit One thing to remember there are differences between limitation and regulation of populations, although they are associated

11. Populations • 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

12. 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.

13. 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)

14. 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

15. 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

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

17. 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

18. Populations • Regulation • Social factors – many individuals want limited resources, this becomes a limiting situation

19. Populations Black-throated Blue Warbler (Dendroicacaerulescens), female at top, male at bottom

20. Populations Pay attention only to the solid line with connecting dots, the others are specific to the paper which I cannot get Here social factors in Red Grouse (Lagopus lagopus scotica) influence population trends

21. Populations • Long-term population trends • These 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

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

23. 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