Factors Affecting Population Change

1. Factors Affecting Population Change 14.3

2. Review: • How did the introduction of zebra mussels affect the health of the Illinois River? • What is a density-dependant factor? • ___________ and ____________ recognized the struggle for available resources within a growing population would inherently _____________ population size. • Examples: ___________________, _________________, _____________________.

3. What is intraspecific competition? • As density increases, there is more ______________ among individuals. • At carrying capacity, _____________ individuals will survive whereas the ______________ individuals will starve or risk death by moving areas. • Building roads?

5. Less resources? • Decrease in individual’s growth/reproductive success. • Harp seals: reach sexual maturity at 87% body weight  if not enough food, slower sexual maturity  decrease fecundity. • Predation? • Many prey go for larger populations  easier to catch. • Predators regulate population. How? • How have caribou populations been disturbed by humans?  need to share habitat with wolves. • Disease? • Why?  pathogens able to pass from host to host with greater ease • Overcrowding.

6. Low density? • All plant and animal species suffer decrease in per capita rate of increase as populations reach small sizes or low densities. ALLEE EFFECT. Finding mates, social interactions requiring high density Ex// passenger pigeon: hunted. Declined in numbers.  could only lay one egg per nest  last one died in 1914. Therefore, harder for pop. To recover with species with low fecundity.

7. Small population • Results in inbreeding and loss of genetic variation. • Minimum viable population size? • Smallest number of individuals that ensures the population can persist for a determined interval of time. • So pop can cope with variations in natality and mortality, environmental changes and disasters. • Used to figure out which species at risk.

8. What are density- independent factors? • Changes in size not related to population density • Human intervention, weather changes, disasters. • Ex// thrips: small insect: consumes many different plant species that food supply is not a limiting factor. • Do no breed in cooler temperatures • Regardless of population density

9. Biomagnification • Increase of a substance throughout a food-chain. • One predator consumes 100 prey which consume 10,000 blades of grass EACH which was treated with DDT.

10. Limiting Factors... • Prevent populations from achieving their biotic potential. • What was this again? Biotic potential: the maximum rate a population can increase under ideal conditions. • Limiting Factor: any essential resource that is in short supply or unavailable. • Determines how much an individual or population can grow. • Ex// a plant requires nitrogen, CO2, and sunlight for growth. If all other factors are available, but nitrogen is used up, N is the limiting factor.

11. Overshooting the Carrying Capacity • Too many births/immigration may result in population overshooting its carrying capacity. • When pop. Surpasses carrying capacity of habitat, d> b = population decrease.

12. Interactions within Communities 14.4

13. Community • All populations in a given ecosystem at a given time • Interact with each other directly or indirectly. • Some organisms cannot exist independantly of one another • Ex// flowers/insects.

14. Ecological Niches Ecological Niche: an organism’s biological characteristics, including use of and interaction with abiotic and biotic resources in its environment. • Fundamental Niche: • Biological characteristics of an organism and the set of resources that individuals in the populations are theoretically capable of using under ideal conditions. • However, organisms face interspecific competitionwith other organisms which use the same resources. • Interspecific competition: BETWEEN SPECIES. • Realized Niche: • (ex// a lion may compete for food with vultures and hyenas) • The biological charatceristics of the organism and the resources individuals in a population actually use under the prevailing environmental conditions.

15. Types of competition within a community (review) • Intraspecific: b/n individuals of same species • Interspecific: b/n individuals of different species.

16. 5 Ways to Classify Interactions b/n species within a community... Symbiosis: various interactions in which two species maintain a close, usually physical, association; includes parasitism, mutualism, and commensalism.

17. Interspecific Competition • Between individuals of different populations. • Restricts population growth. • Interference competition  actual fighting over resources • Tree swallows + bluebirds for birdhouse • Exploitive competition  consumption or use of shared resources. • Two predators rely on same prey (arctic foxes and snowy owls both prey on same pop. Of arctic hares)

18. Gause’s Principle • 1934 • “The Struggle for Existence” • Two species with similar requirements could not coexist in the same community. • The more niches that overlap, the greater the competition. • One species consumes most of the resources, reproduces more efficiently  inevitably drive other species to extinction. • CONCLUSION: if resources are limited, no two species can remain in competition for the same niche indefinetely. • COMPETITIVE EXCLUSION

19. Interspecific Competition (Con’d) • Resource Partitioning (Animals) • Individuals of the same species avoid competition for similar resource • Ex// birds or lizards (of same species) occupy different perching/nesting/eating sites. • Reduces interspecific competition • Increases likelihood of species surviving. • Resource Partitioning (Plants) • Annual plants: foxtail, mallow, smartweed • All require similar nutrients from the same habitat • Each evolved unique ways to survive in the presence of each other • Foxtail: shallow, fibrous roots  absorbs water from surface of soil • Mallow: deep taproot system  grow deeply down into soil/obtain moisture later in growing season • Smartweed: branches both in the topsoil and soil below the roots of other plants: “best of both worlds”

21. Predation • Interspecific interaction  why? • When prey population increases, predator population can increase  why? • Reduction of prey results in a decline in predator population... Unless it has access to another food source.

23. Cyclical patterns of predator-prey relationships • Two species cycle slightly out of synchronization • Predator lags behind prey

24. Describe what is happening at Time: A) B) C) D) E)

25. Defence Mechanisms • Prey have adapted unique ways to detour predators • Thorns, hooks, spines, needles, chemicals (plants) • Mustard family (pungent odour) • Balsam fir (chemicals that mimic an insect growth hormone  when linden bugs feed on balsam fir, remain in juvenile stage and eventually die) • How would this help the balsam fir?

26. Defence Mechanisms (2) • Monarch Butterfly • Consumes toxins (not toxic to itself)  is distasteful to its predators. • Butterflies start out as caterpillars (ie. larvae)  feed on milkweed  through metabolism milkweed becomes unpalatable. • Blue jays don’t ‘finish’ eating monarch butterflies.

27. Defence Mechanisms (3) • Passive or Active • Passive: hiding • Camouflage (cryptic colouration) • Bright colours: warn predators of chemical defence mechanisms (poisons) • Monarch butterfly • Wasp (hover fly?) • Lethal octopus, Haplochlaenamaculosa: pattern (rings) contract and expand as warning signal. • Active: fleeting • Alarm calls  to mob the predator

28. Different types of defense mechanisms (Are the animals ‘meaning’ to do this?)

29. Defense Mechanisms (4) • Mimicry • Mimic resembles distasteful/harmful species • Batesian • Palatable/harmless species mimics unpalatable/harmful organism • Ex// Viceroy butterfly  monarch • Mullerian • Several unrelated species that resemble one another and are all poisonous/dangerous. • “pooling of numbers` causes predators to learn more quickly to avoid these species.

31. Independent Reading • Read pages 684-687 (Symbiosis & Disruption of Community Equilibrium) • Define/understand all of the definitions: • Mutualism, commensalism... Macroparasites, etc. • Relate definitions to example species (in text)

32. Seatwork/Homework • Page 688, #1-7