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Population growth Reproduction, births, natality (B) Immigration (I) Population Mortality, death (D) Emigration (E) Adult survival, juvenile survival, and fecundity are what we need to estimate λ, the intrinsic population growth rate. 1.8 Winter Wren 1.6 Source/ growing populations 1.4 Lambda 1.2 Stable population 1.0 0.8 0.6 0.4 Sink / declining 0.2 0.0 Reserve Changing Developed Landscape Developed Changing Apparent Survival se Juv 0.15 0.13 0.14 0.08 0.17 ** 0.03 0.21 0.06 0.18 0.07 0.16 0.19 0.11 Species American Robin Bewick's Wren Dark-eyed Junco Song Sparrow Spotted Towhee Swainson's Thrush Winter Wren Fecundity 0.59 0.92 1.37 1.13 0.57 0.40 1.23 var 0.08 0.88 0.15 0.46 0.12 0.07 0.08 Adult 0.4 0.29 0.5 0.54 0.5 0.46 0.35 American Robin Bewick's Wren Dark-eyed Junco Song Sparrow Spotted Towhee Swainson's Thrush Winter Wren 0.89 0.78 1.10 1.23 0.82 0.40 0.61 0.16 1.33 0.38 0.21 0.46 0.07 0.33 0.55 0.32 0.47 0.54 0.55 0.53 0.38 0.12 0.08 0.09 0.02 0.03 0.04 0.08 0.71 0.14 0.5 0.51 0.54 0.59 0.54 0.22 0.06 0.17 0.06 0.06 0.1 0.12 Reserve American Robin 0.80 0.13 Bewick's Wren 0.84 0.16 Dark-eyed Junco 0.55 0.50 Song Sparrow 0.81 0.37 Spotted Towhee 0.74 0.15 Swainson's Thrush 0.50 0.06 Winter Wren 0.61 0.09 * Upper 95% CI Limit of parameters used for calculating λ 0.04 0.05 0.05 0.08 λ 0.5416 0.4526 0.7543 0.827 0.6563 0.5719 0.5823 Upper λ * 0.962 0.9243 1.158 1.022 0.8795 0.7886 1.207 0.18 0.08 0.14 0.18 0.18 0.17 0.1 0.08 0.03 0.05 0.03 0.03 0.04 0.03 0.7606 0.4566 0.6924 0.8125 0.7475 0.6368 0.5016 1.102 0.7325 0.9812 0.9273 0.9013 0.7744 0.7522 0.31 0.03 0.15 0.16 0.18 0.21 0.18 0.23 0.02 0.09 0.04 0.04 0.08 0.08 0.9666 0.2435 0.6308 0.6962 0.724 0.7332 0.6974 1.443 0.4885 1.176 0.9349 0.9245 0.9873 1.057 se 0.08 0.05 ** Changing Juv survival estimate used in calculating λ From Oleyar et al. (in prep) 1.8 Song Sparrow 1.6 No obvious response in growth rate by landscape. 1.4 1.0 0.8 0.6 0.4 0.2 0.0 Reserve Changing Developed 1.8 Spotted Towhee 1.6 1.4 1.2 Lambda Lambda 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Reserve Changing Developed 1.8 1.8 Winter Wren 1.4 1.4 1.2 1.2 1.0 0.8 0.8 0.6 0.4 0.4 0.2 0.2 0.0 Reserve 1.8 Changing Developed American Robin 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Reserve Changing Reserve Changing Developed Declining λ outside of reserves? 1.6 Lambda 1.0 0.6 0.0 Swainson's Thrush 1.6 Lambda Lambda 1.6 Developed 1.8 Dark-eyed Junco 1.6 Possible sink during development for some species followed by recovery as subdivision ages? 1.4 1.0 0.8 0.6 0.4 0.2 0.0 Reserve Changing Developed 1.8 Bewick's Wren 1.6 1.4 1.2 Lambda Lambda 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Reserve Changing Developed •Are developed landscapes ecological traps for Robins? Number detected within 50m during 10mins •Robin numbers ‘stable’ but low in reserves, highest in developed residential areas Number detected within 50m during 10mins •Winter Wren numbers high and ‘stable’ in reserves, low and/or declining elsewhere 2.0 2.0 Number detected within 50m during 10mins How do these projections match up with what we see out there? 2.0 Winter Wren American Robin Swainson's Thrush Reserves 1.5 1.0 0.5 0.0 Changing 1.5 1.0 0.5 0.0 Developed 1.5 1.0 0.5 0.0 1999 2000 2001 2002 2003 Year 2004 2005 2006 2007 Populations fluctuate due to • Density dependent factors – Ex: Predation, competition, habitat availability – change population growth in predictable ways – N is driven by population density • Density independent factors – Random or Stochastic events – Ex. Weather, accidents – Breeding 14 aug 2007 Definitions • Population regulation: the tendency of population sizes to stay within a certain range # of Animals (N) time Carrying capacity Carrying capacity (k): the number of organisms that can be supported by a given area; the actual number of organisms fluctuates near this # of Animals (N) k time Population fluctuations Carrying capacity (k) k N N time Classic growth curve, unlimited resources time Classic growth curve, limited resources (k) Population fluctuations Example of unlimited growth: Australian rabbit (European hare) • 1859: 24 hares introduced (for human food?) • 1865: over 20,000 hares were harvested, actual population much greater. • Mid-1800’s to mid-1900’s: major problem with too many hares; caused habitat destruction and reduction in native mammals • 2000: still present, local problems Carrying capacity Rabbits exceeded k No rabbits Rabbit-proof fence Population regulation: food High food addition Low food addition Townsend’s vole No food added Shaded area is winter Population regulation: food Population size Population cycles: Ex. peaks in lynx populations show time lag behind peaks in snowshoe hare populations Snowshoe hare Lynx Time (years) Population regulation: climate Population regulation: competition • Competition – demand by 2 or more individuals of the same or different species for a common resource • Between 2 individuals of same species: Intraspecific • Between 2 individuals of different species: Interspecific • Limited supply of resource: Exploitation • Not limited but interaction detrimental: Interference Inter- or Intraspecific competition? Exploitation or Interference competition? Population regulation: competition Niche A portion of the feeding niche of the Blue-gray Gnatcatcher (Smith & Smith 1998) Foraging height (m) Niche: an n-dimensional hypervolume which includes the range of biological and physical conditions under which an organism can exist, including the resources that an animal must exploit for growth and reproduction Prey length (mm) Interspecific Competition • Food sources (both what and where) • Nest or Den sites • Interspecific competition can lead to resource partitioning, and expression of a ‘realized niche’ versus a species ecological niche. Predator-Prey Relationships What are predators? • Animals that kill and eat other animals (prey) • At or near the top of the trophic pyramid Major predators of the Arctic NWR Polar Bear Grizzly Bear Ermine Arctic fox Wolf Snowy Owl Predation in Natural Communities Almost all animals have significant predatorsexceptions are: Herbivores: Top predators: Bison Grizzly bear Elephant Lions Rhinoceros Polar bear Hippopotamus Killer Whale Human Attitudes and Predators • Human perspectives – Little Red Riding Hood – The Three Little Pigs • Human persecution Why? • Domestication of animals • Protection • Entertainment Overcoming History • Old attitudes die hard • Urban residents and predators Predator-Prey Relationships Response to Prey Functional Response • Tendency of the predator to eat more of a prey species as the prey become more abundant Predator-Prey Relationships Prey Attacked Attacked ## Prey Functional Response 80 80 60 60 40 40 20 20 00 00 20 20 40 40 Prey Prey Density Density 60 60 Predator-Prey Relationships Response to Prey Numerical Response • Number of predators increases with an increase in the density of prey animals Predator-Prey Relationships Numerical Response (Buckner and Turnock 1965) Sawfly Juveniles Sawfly adults Birds High Density (N/km2) 5,280,000 Low Density (N/km2) 98,800 507,500 11,600 58.1 31.1 Annual cycle of a prey population Percentage of Population 100 Energy shortages Energy shortages Accidents Disease Accidents Predation Disease Predation J F M A M J J A S O N D Population Cycles Population Cycles Adaptations to cyclical prey cycle? Dispersal Prey switch Reproduction Isle Royale Isle Royale • Size: 45 miles long x 9 miles wide • Protection: National Park established in 1940 Wilderness designation in 1976 National Biosphere Reserve 1980 • A location of a long term study of the relationships between the moose and gray wolf Historically, two large ungulates occupied Isle Royale: Woodland Caribou Moose Isle Royale Settlers arrived in late 19th century Responsible for fire and forest cutting Moose cross ice from Minnesota and establish early 20th century Fires change old-growth coniferous forests to younger deciduous forests Moose outcompete woodland caribou Caribou became extinct on the island Wolves arrive 1950 by crossing ice Wolf Response to Moose Functional Response: lots of moose • Possible because wolves are cooperative hunters Numerical Response: lots of moose • wolves reproduce well • Immigration is unlikely since it depends on Lake Superior freezing (uncommon) Moose Response to the Wolf • Most vulnerable moose are the very young and the old (infirm) • Most killed moose show signs of malnutrition and disease (i.e. they are more vulnerable) • Males most vulnerable: go into winter in relatively poor shape because of rut Wolf Population Three major factors that control the wolf population: 1. Moose numbers 2. Linear dominance hierarchy in wolf population 3. Genetic diversity (inbreeding effects)