C4.1 Populations & Communities (18)

C4.1.1+4+10

• population =  group of organisms of same species, same area, time (inc. by birth/immigration, dec. by death/emigration)

• community = group of populations living tog./interacting in same area (plants, animals, fungi, bacteria)

  • interact w/ habitat to form ecosystem where each species occupies niche

• motile species size → capture-mark-release-recapture

  • M = no. of individuals captured in defined area, marked, released

  • N = no. of individuals recaptured after set time

  • R = no. of marked individuals in recaptured sample

• lincoln index for population estimate: M x (N/R)

  • assumptions: random sampling, marked individuals randomly distributed, marking individuals will not influence mortality/natality of population, marking remains visible, population size doesn’t sig. change between periods of capture

C4.1.2–3 Estimation of population size by random sampling +

• populations fluid + change (some impractical to count)

  • diff. between estimate + true size = sampling error 

• random sampling → sampling point positions randomly selected to avoid bias (e.g. establishing grid + randomly picking coords)

• systematic sampling → sampling point positions at fixed intervals in target area (allows for investigation of effects of environmental factors on species distribution via transect)

• population size/distribution of non-motile species → quadrat sampling

  • quadrat (rectangular frame) placed inside defined area (randomly/transect), no. of species counted/estimated via % coverage

    • repeat many times to find mean + SD

C4.1.5–6 Carrying Capacity + Negative feedback control of Population size by density-dependent factors

• carrying capacity = max. no. of individuals in species that environ. can support

  • species w/ high growth/low survivability fluctuate markedly around CC (r)

  • low growth/high survivability have more stable levels at CC (k)

  • populations oscillate around this, not static value but influenced by a/biotic factors 

• population size impacted by density-dependent factors pushing them back to CC

  • higher density → more competition, low-density → grow more

  • - feedback loop (inc. pop. density → reduced size bc of these factors)

Predation, Access to habitats, Nutrient supply, Diseases, Accumulation of waste

C4.1.7–8 Population growth curves + modelling

• stable populations → S-shaped curve

  • exponential → initially slow, numbers accumulate + rapid inc., mortality low bc abundant resources + min. environmental resistance

  • transitional → resources become limited as population grows → competition. natality dec., mortality inc., slower growth

  • plateau phase) → mortality = natality, population growth static. reaches carrying capacity of environment, limiting factors keep it stable (oscillate around carrying capacity)

• modelled using simple organisms in lab (yeast, duckweed) bc small, low requirements, rapid repro.

  • yeast growth measured growing in broth culture + measuring turbidity (cloudiness)

  • duckweed in petri dish w/ liquid fertiliser + light source

C4.1.9+11

• intraspecific interactions = cooperation (+/+) + competition (+/-)

  • cooperation = pack animals hunt tog. to feed, insects work tog. to build nests + find food

  • competition = woodland trees competing for light/water/mineral access, territorial animals defending their space, M mating w/ F

• herbivory (+/+ e.g. bee/pollen or +/- e.g. cow/grass)

• predation (+/-) e.g. owl/mice, lion/zebra, wolf/deer

• interspecific competition (+/-) direct e.g. territory/indirect e.g. depleting resource

  • lions/hyenas, beech/pine

• symbiotic relationships = 2 species interact closely long-term

  • mutualism (+/+), commensalism e.g. barnacle/whale (+/0), parasitism e.g. tick/canine (+/-)

• pathogenicity = infectionism micro-org live inside host, cause disease

  • bacteria causing TB in animals

C4.1.12–13 Mutualism + Invasive Species

• root nodules (legumes gain nitrates/rhizobacterium gain carbs)

• mycorrhizae in orchids (fungus connects to plant roots + inc. SA for abs., plant gives nutrients)

• zooxanthellae in polyps (zooxanthellae photosynthesis for nutrients for polyp/polyp’s CaCO₃ exoskeleton provides shelter)

• endemic → native, alien → transferred 

  • if alien has - effect on existing chains → invasive

  • normally have large fundamental niche, repro. rapidly, lack predator, have features suited to new environ.

• red fox introduced to australia by european colonisation → apex predator that has common diet  + niche w/ native quoll (size declined sig.)

C4.1.14–15

• comparative distribution of species indicates their relationship type

  • inter. comp. indicated if 1 is more successful in another’s absence

  • lab experiments under controlled conditions by measuring DV when both species present/isolated

  • field manipulation via selective removal of species to determine its impact on the other in natural environment

  • field observations where random sampling sites assessed (quadrats) for presence/absence of each species 

• quadrat sampling → chi-squared test

  • if found in same habitat → + association e.g. predator-prey

  • if don’t occur in same habitat → - association e.g. inter. comp.

C4.1.16

• predator-prey dynamic means their populations lvls intertwined

  • = density-dependent population control mechanism

  • but most may not show clearly bc predators have multiple food sources, prey have multiple predators

  • prey drops → predator drops after bc more competition

  • prey rises → predator inc. bc over-abundant food source

C4.1.17–18

• top-down control → higher trophic lvls exert pressure to control ecosystem’s pop. dynamics e.g. keystone species to prevent monopoly

  • oscillating trophic cascade  (- ← + ← -) 

  • consumer suppresses food source abundance / alters competitor's behaviour to impact lower trophic levels

• bottom-up control → pressures applied to lower trophic lvls e.g. plants limited by light intensity. to impact abundance of animals at higher trophic levels by restricting E supply

  • - → - → - 

  • (one more likely to dominate, can switch)

• organisms can exert control over other species by releasing chemicals

  • allelopathy → releases chem. that influence growth/survival/repro. (+/-)

    • e.g. garlic mustard plant reduces germination + root growth of other species

  • antibiotics → releases chemicals that neg. affect bacteria by targeting prokaryotic-specific features (inhibit growth/kill it)

    • e.g. penicillium releases penicillin, preventing bacteria cell wall formation