Limiting Factors and the Law of Tolerance

1. Limiting Factors and the Law of Tolerance – limiting factor - a single component/resource that limits population growth Examples: – black bear - territorial space – bald eagle - large nesting trees near water – predator populations (carnivorous fish, mammals) – prey availability – when we can identify one or more limiting factors for a population we can control the size of the population; we can increase a game population (quail) or decrease pests (rock dove, house sparrows, rats and mice) – Shelford’s law of tolerance - a species tolerance of ecological minimums and maximums with regard to various conditions; conditions (some feature of the habitat) are

3. optimal for a species in certainareas, and density decreases the further removed individuals are from optimal conditions Examples: – snow cover and cold temps limit how far north quail can live –oxygen levels determine which fish species can live in an aquatic system Dispersion patterns and dispersal – dispersion - spatial pattern or distribution pattern of individuals in a population; can have random, clumped, and uniform patterns – dispersal - outward movements of individuals away from their established areas of activity; some animals must leave natal areas (place of birth) and establish new territories; resources may run low if all new individuals remained in the same location

4. Dispersion Patterns of Populations Ordered = Uniform

5. – migration - 2-way movement to and from an area on a regular basis (seasonal) or corresponding to a life history change (salmon migrations) 2 types: – emigration - migration out of an area – immigration - into an area – we can endanger less mobile species by erecting barriers that restrict movement; dams for migrating fish (sturgeon, salmon), clearcuts for amphibians Zoogeographic regions - continents or portions that are relatively isolated from one another in terms of dispersal of animals – we’re in nearctic – exotics - organisms introduced from another region

7. – transplant - organism moved outside its native region but • within same zoogeographic region; both transplants and • exotics are introduced organisms • Examples: • exotic - brown tree snake introduced to Guam and other • Pacific islands • transplant – several fish species taken from SE U.S. to Pacific • Coast (crappie, bass, sunfish) • – native range - geographic area in which the species is • originally found • – naturalized organisms - introduced species that reproduce • in new area • Examples: • rainbow trout from Pacific coast to eastern U.S. • ring-necked pheasants from SE Asia to Midwest • European house sparrow and starling

8. Brown Tree Snake (Boiga irregularis) • Introduced to Guam in 1950’s and • had spread over island by 1970 • Caused extinction in 12 native • species of birds and several others • are barely hanging on Over 1200 power outages due to the snake since 1978 Introduced or seen on 9 other Islands including Hawaii; also Texas

9. – feral animals - reverted to wild state after being domesticated; horses and pigs in U.S. – restored species – eliminated from portions of native range and then successfully released on these vacated portions of native range; California condor and wild turkey in U.S. Population Dynamics - study of changes in numbers or weight of organisms in populations – affected by 3 functions: natality (birth/new individuals), growth (biomass), and mortality (individuals die) – these 3 functions influence population structure and population structure is assessed by measuring population size, age distribution, and sex ratio

10. – density-dependent and density-independent factors: dependent - environmental factor that affects a population based on its density Example: elk overgraze and then compete for food; this stresses the herd and fewer cows produce young, body size decreases, mortality increases independent - factor that acts independently of population density Example: a harsh winter with cold temps and deep snow affects individuals and is independent of what happens to others in the population – natality - birth or hatching; # of young born or hatched within a specified period of time Examples: all fawns born to deer herd in a year; measured as # of offspring/1000 female

11. for fish we use recruitment; measured as # of fish hatched that survive to reproductive size – growth - gain in body size — birds and mammals have determinate growth, fish have indeterminate growth (never really quit growing) — determinate – most large mammals reach adult size in 1 or 2 years; smaller body size can occur at high densities but mortality is more likely to be affected — indeterminate - growth patterns variable; growth is density dependent and could have high density, slow growing population (stunted population); yellow perch can get up to 260 g after 4 yrs at low densities, but about 20 g after 4 yrs at high densities (about 7.5% body size of low density perch)

12. – mortality - death; % of pop that dies in one year; mortality cause can be density dependent (DD) or independent (DI) — DI - winter blizzard kills individual pheasants — DD - winter shelter can only protect a certain number of birds so the rest are left without cover and die – natural mortality - caused by predation, starvation, diseases, accidents, etc. – harvest mortality - caused by human activities such as trapping, hunting, and fishing; really another type of predation – harvestable surplus - if a certain % of the population will die due to natural mortalityand DD factors, then harvest mortality can benegligible to an extent

13. Example: bobwhite quail have about 70% natural mortality/yr so if you harvest 35% of pop then 35% of pop will die of natural mortality; the part harvested is called compensatory mortality; if harvest goes above natural mortality then it is called additive mortality – additive mortality can be avoided by hunting regulations (seasons, bag limits); we must know population parameters; additive mortality is not always negative to have, white-tailed deer need it now in the SE U.S. and regulations are becoming more liberal (a doe and buck/day during season)