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Biogeography Exam 2 with
complete solution 2026
Population genetics - ANSWERS-a group of interbreeding individuals Population Ecology - ANSWERS-a group of individuals of the same species inhabiting the same area exponential growth - ANSWERS-Density Independent Growth solving for population at time t: Nt = N0e^rt Nt = population size after t generations. N0 = initial population size. e = base of the natural logarithm population growth - ANSWERS-can be exponential or logistic Doubling time - ANSWERS-the time taken for a population to double it's size logistic growth equation - ANSWERS-dN/dt = rN(K-N/K) The closer N gets to K the slower the rate of growth. Density Dependent Growth. K - ANSWERS-carrying capacity in number of individuals of a species (how many individuals can an environment support) R-strategist - ANSWERS-- named after the intrinsic growth rate, r, in population growth equation
- They continually colonize temporary habitats, are opportunistic, have high growth rates, high fecundity, and short generation time, put little effort into raising young so many will perish.
- Migration is a major component of their population dynamics, often colonize areas free from rivals. Pioneer species, and they are often poor competitors American oyster - releases up to 100 million eggs in one season. K-strategist - ANSWERS-- named after the carrying capacity parameter, K, in population growth equations They live in stable environments, where the generation time is less than the habitat's 'life-span'.
They are often large, long-lived, very competitive, have low birth and death rates, and invest time and effort in raising offspring They are unlikely to degrade habitat and overshoot the carrying capacity. What are some examples? Most large mammals, e.g. elephant, human. Metapopulations - ANSWERS-a group of spatially separated populations of the same species which interact at some level Extinction-and-colonization metapopulations - ANSWERS-... Big Horn Sheep - ANSWERS-have metapopulation in Southern California. Resident populations are found mountain ranges, but research shows intermountain movements. The range is bounded by fenced highways. See slide for study example Loose metapopulations - ANSWERS-A set of populations of the same species, where rates of mating, competition, and other interactions are much higher within the subpopulations than they are between the subpopulations Tight metapopulations - ANSWERS-A set of conspecific subpopulations living in a mosaic of patchy habitats, with a significant exchange of individuals between patches Occurs where the distance between habitat patches is shorter than the species is physically capable of traveling, but longer than the distance most individuals move within their lifetime Source-sink (mainland-island) metapopulation - ANSWERS-consists of a mixture of small subpopulations prone to extinction and a large persistant population Habitat - ANSWERS-A region or area where a species or population usually lives, characterized by a specific set of environmental conditions, such as light availability, temperature, moisture, salinity, disturbance regime, etc. Habitat specialist - ANSWERS-organisms with very percise living requirements. Example: gopher tortoise Habitat generalist - ANSWERS-organisms that are able to live in a great array of environments (Homo sapiens, roach) Habitat fragmentation - ANSWERS-the breaking up of large habitats or areas into smaller parcels. It is enormously significant for wildlife and poses a global problem Community Changes from habitat fragmentation - ANSWERS-The numbers of generalist species, species that can live in more than one habitat, edge species, and exotic species all rise. The nest predation rate rises, populations fall, and extinctions become more common.
Thalassochory Hydrochory Biological Agents of seed dispersal - ANSWERS-Biochory Isochory Anemochory - ANSWERS-wind dispersal of seeds Thalassochory - ANSWERS-sea dispersal of seeds Hydrochory - ANSWERS-fresh water dispersal (streams or lakes) Biochory - ANSWERS-use other organism in some way (attach to them, inside fruit that get eaten) Ichthyochory - ANSWERS-movement of seeds by fish Subaceous Hydrochory - ANSWERS-Aquatic plants like spider lily disperse seeds that immediately sink and try to establish in the substrate. the seeds need a high water velocity to be moved downstream Best dispersers - ANSWERS-birds, bats, insects, spiders Average dispersers - ANSWERS-lizards, tortoises, rodents Worst dispersers - ANSWERS-large mammals, freshwater fish (obligates) A dispersing organism will fail - ANSWERS-if it cannot colonize a new location colonizing ability - ANSWERS-Disperal ability does not necessarily equate with Environmental factors include - ANSWERS-physical (climate) or biotic (competition). Failed dispersers - ANSWERS-either could not move a long distance or withstand environment during travel or on arrival, or could not establish a viable population Reluctant dispersers - ANSWERS-may maintain a colony but do not spread in the new location Rampant dispersers - ANSWERS-invasive exotics Examples: Kudzu, loose strife, zebra mussels, tamarisk, european starling Landscape ecology's influence on dipersal - ANSWERS-the arrangement of landscape elements in a landscape mosaic affects the ease with which animals and plants may move through a landscape
Landscape resistance - ANSWERS-describes the ease of move ment of organisms through a landscape Patch-corridor matrix - ANSWERS-Frequently used in landscape ecology to explain species patterns and dynamics Patch - ANSWERS-fairly uniform area that differs from it's surroundings (forest, field, pond, rock outcrop). Patch size - ANSWERS-affects the occurrence of species. Larger patches tend to have more species (habitat diversity) and more interior species. Smaller patches have lower species diversity and more edge species. Corridor - ANSWERS-strip of land, or water that differs from the area on either side and links together patches (hedgerow, riparian corridor) Matrix - ANSWERS-background ecosystem or land-use type in which the patches and corridors and found (agricultural fields, suburban development, forests) Simpson's Levels of dispersal difficulty - ANSWERS-Level 1 - corridors Level 2 - filter routes Level 3 - sweepstakes routes Level 1 - corridors - ANSWERS-routes through hospitable terraine that allos unhindered passage in both directions filter route - ANSWERS-some migrants are barred, e.g. Alaska/Siberia landbridge during the Pleistocene with arctic climates sweepstakes route - ANSWERS-small number of winners, or those that manage to survive the journey to colonize a distant place Panama as a filter route - ANSWERS-See dispersal slides 20 -23 for Panama as an example of a filter route Disturbance - ANSWERS-any relativly discrete event in time (fire, wind, pest outbreak) that disrupts ecosystems, community, or population structure, and changes resource availability or the physical environment Scale - ANSWERS-...Minimum size depends on the size and home range of the organisms Maximum size can be any size depending on the disturbance (catastrophic volcanism, or humans and global climate change)
Younger individuals - ANSWERS-are more productive than older individuals Intermediate Disturbance Hypothesis - ANSWERS-Species diversity is low at low disturbance frequency because of competitive exclusion. Species diversity is higher at intermediate disturbance frequency due to the mix of good colonizers and good competitor species Species diversity is low at high disturbance frequency because only good colonizers or highly tolerant species can persist, "weedy species". Temporal influence of IDH - ANSWERS-"intermediate time scale" - traditional IDH concept focuses on frequency of disturbance Does disturbance happen before recovering species are big enough to withstand the next event or reproduce, or colonize? Spatial influence of IDH - ANSWERS-Between patch - many disturbances create a mosaic of disturbed and undisturbed patches, so r-strategists coexists in different patches. Dispersal is important. Within patch - many species i.e especially plants go through life stages that can withstand disturbance i.e. seeds, tubers, roots. Fire - ANSWERS-rapid oxidation (combustion) of a fuel source (carbon based organism) requires fuel, oxygen, ignition source Vertical and horizontal connectivity of fuel - ANSWERS-In forests without connectivity of fuels upward (standing dead snags, or dead logs leaning on live trees) then the fires may not burn into the canopy. Dead vegetation - ANSWERS-burns better so the balance between amounts of dead and living is an important determinant of fire intensity. Production vs. Decomposition - ANSWERS-The relationship of the rates of production, decomposition influence fuel availability. Both are influenced by climate, both are greater in warmer wetter environments. Decomposition rates vary more than production, in colder or drier environments decomposition really trails off, but productivity can stay higher in these conditions and fuel accumulates. Herbaceous areas in the understory can cause frequent fire because they are highly productive, accumulation > decomposition, and dry out quickly influences on fire - ANSWERS-Surface area Presence of volatile chemicals Atmospheric conditions Atmospheric conditions that affect fire - ANSWERS-- Dry conditions and hot - dries fuel
- Wind - helps dry fuel and spread fire
- Ignition source - lightning frequency and human presence.
- Strong seasonal climate variability in high fire areas Fire types - ANSWERS-Ground fire Surface fire Canopy fire Ground fire - ANSWERS-most common when organic layer is dry in the soil, histic soil Surface fire - ANSWERS-consumes fuels on the surface and upward only a couple of meters at most, but not into canopy More frequent than canopy fires. Above ground parts of small plants will be consumed. Savannahs and prairies have these fires mainly. Canopy fire - ANSWERS-burns into the canopy layer Most intense and severe. Dominates boreal forest and most forests in the mountain western U.S. Fire effects - ANSWERS-Landscape Ecological Landscape affects on fire - ANSWERS-Creates heterogeneity in landscape Position of Ecotones Yellowstone example - ANSWERS-Review Yellowstone example in disturbance lecture Results of fire creating heterogeneity in the landscape - ANSWERS-Increased diversity in the landscape mosaic. Decrease in disease spread and pest outbreaks. Fuel accumulation mosaic that affects future fire spread. Position of ecotones - ANSWERS-Fire may help maintain prairie-forest ecotone or woodland-steppe ecotone. Mangrove Ecotone - ANSWERS-Ecotone begins in coastal marsh dominated by sawgrass and terminates in mixed mangrove forest. After a fire occurred in the marsh in September 2000, they found that this ecotone shifted 20m towards the river. Then a freeze event in January 2001 pushed it another 20m towards the river. Ecological effect of fire - ANSWERS-Nutrient Availability Light regime and microclimate Soil stability Moisture and water availability
Apical dominance - ANSWERS-all effort is put in one trunk or shoot upward, after fire this tendency may change to multiple trunks or shoots. Blood Mountain Wilderness - ANSWERS-Review Blood Mountain Wildness in disturbance lecture (slide 28, 29) Wind - ANSWERS-damage results from a number of types of events, of varying speeds like multidirectional tornados, and hurricanes, or unidirectional gale and windstorms Types of Wind Damage - ANSWERS-Uprooting, blowdown, windthrow Branch breakage Defoliation Drying of leaf tissue Stem (trunk) snapping, basal shear Indirect damage Pit-and-mound topography - ANSWERS-uprooting create a pit where the roots were located, and a mound of topsoil dirt was attached to the roots. Creates microclimates and exposes nutrients and affects soil moisture Pits - ANSWERS-have mineral soil, subsoil, exposed. Mounds - ANSWERS-are organic rich, and decomposition of roots will add to that. Biotic influence of wind damage - ANSWERS-Size of plants Deciduous vs coniferous Forest density Pathogens or pest Abiotic influence of wind damage - ANSWERS-Soil structure Topography Proximity to ocean Type of storms (higher wind speed, more damage; greater precipitation, more uprooting Biological responses to wind damage - ANSWERS-- Advance regeneration layer released - a midstory tree that was supressed before disturbance starts to grow quickly after
- Resprouting of damaged trees.
- Seed germination in changed understory.
- Lateral growth of gap edge trees.
- Increased vulnerability of trees to subsequent disturbance if weakened or damaged. Chestnut blight example - ANSWERS-caused by the sac fungus (Cryphonectria parasitica) which was introduced in N.Y. City around 1904 on Asian Chestnut nursery plants. Destroyed the entire American chestnut species in 40 years.
- Changed the eastern hardwood forest community from oak-chestnut to oak-hickory, with several oaks, beech, hickories, tulip popular, and red maple becoming co- dominant.
