Ecology 3 PDF

# Communities + interactions - refers to all species that occur together at any particular locality - assemblage: refers to only subset of species occurring in community - abiotic environment + interaction between species determine type of species that occur together in a community ## Population I...

# Communities + interactions - refers to all species that occur together at any particular locality - assemblage: refers to only subset of species occurring in community - abiotic environment + interaction between species determine type of species that occur together in a community ## Population Interactions and Their Effects | Interaction | Effects on Interacting Populations | |:---|:---| | Predation | Predators gain nutrients and energy; prey are killed or injured. | | Herbivory | Herbivores gain nutrients and energy; plants are killed or injured. | | Parasitism | Parasites gain nutrients and energy; hosts are killed or injured. | | Competition | Both competing populations lose access to some resources. | | Commensalism | One population benefits; the other population is unaffected. | | Mutualism | Both populations benefit. | ## Predation + Herbivory 1. predation: interaction between predators + their prey - consumption of one organism by another → carnivores 2. herbivory: interaction between herbivores + plants they eat - predators of plants 3. both have evolved specialised behaviours + anatomical structures that help them obtain + consume food 4. specialists: feed on one or few types of food 5. generalists: eat wide variety of food ## Interactions between ecological processes 1. predation is density dependent + lowers competition 2. removal of predators → lead to population explosion of predated species + extinction of other 3. too many prey species → one species will outcompete the other 4. predators allow different species to coexist ## Defenses against herbivores 1. spines, thorns, irritating hairs + chemicals deter herbivores from feeding 2. other compounds mimic structure of insect hormones → disrupts development of insects that consume them 3. some increase production of toxic compounds in response to herbivores feeding 4. some herbivores have coevolved ability to recognise certain odours + avoid toxic plants 5. others evolve defences against plants ## Passive defences against predation 1. mimics: look like something unappetizing can hide in plain sight e.g. caterpillars look like bird poop 2. cryptic coloration: helps some prey blend in with surroundings 3. cornered prey may try to startle or intimidate predator with display that increases size or ferocity 4. some species hide in protected site ## Active defences against predation 1. porcupines release sharp quills that stick to predator's mouth 2. other species fight back by biting, charging or kicking predators 3. some produce chemical defences 4. some insects protect themselves with poisons acquired from plants 5. aposematic (protective) colouration → warning colours that show they are dangerous ## Animal defences against predators 1. some animals feed on plants rich in secondary compounds receive extra benefit e.g. caterpillars that feed on members of milkweed family become poisonous butterflies 2. mimicry: - batesian mimicry: palatable insects resemble bright coloured, distasteful species - mullerian mimicry: unrelated distasteful species resemble one another → predators learn more quickly to avoid distasteful species *Predator-prey coevolution: predators coevolve ways to overcome prey's antipredator defences ## Co-evolution - parallel development of adaptations in population or species that constantly interact with each other - start practice parallel development of adaptation in population or species so will start exert selective pressure on each other - adaptation in reaction to reciprocal selection ## Interspecific competition - occurs when populations of different species use same limiting resources 1. populations may experience increase mortality + decreased reproduction 2. reduces size + population growth rate of one or more of competing populations 1. Interference competition - individual of one specie harm individuals of another species directly - animals may fight for access to resources - plant species may release toxic chemical that prevent other plants from growing nearby 2. Exploitative competition - two or more populations use same limiting resource - presence of one species reduces resource availability for others - no direct confrontations ## Classic experiment: Gause - Russian ecologist 1. studied competition among 3 species of Paramecium growth in culture tubes 2. fed on same bacteria 3. 2 experiments: growing alone + growing together 4. constant carrying capacity 5. fed same bacteria 6. remove waste material 7. monitor population growth over time 8. conclusion: - competitive exclusion principle: two or more species in population that rely on same limiting resource cannot coexist - one species will be more successful - no 2 species can have same niche ## Competitive Exclusion — Gause's Experiment [Image of a graph showing the outcome of Gause's experiment] ## Ecological niche - total ways of utilizing resources in environment - space utilization - food consumption - temp. range - moisture requirements - biotic interactions Habitat: place where organisms live 1. Fundamental niche: environment condition + resource that population can tolerate + use - total niche potential available 2. Realised niche: environmental conditions + resources that population truly use - after competition taken into account - smaller than fundamental niche ## Resource partitioning - occurs as sympatric species: similar species that exist in same geographical area - divide resource to prevent direct competition e.g. one tree → each bird species feeds at different area of the tree - separate niches even though fundamental niche is the whole tree ## Character displacement 1. allopatric populations (living in different places): morphologically similar + use similar resources 2. sympatric populations (live in same place): morphologically different + use different resources 3. caused by interspecific competition 4. changes diet of birds → can lead to speciation ## Parasitism - smaller than prey where they gain something + prey loses something 1. Ecto-parasites: external parasite + have elaborate sensory + behavioural mechanisms e.g. leeches or lice 2. Endo-parasites: internal parasite + completes life cycle in 1/2 hosts 3. Parasitoids: insects that lay eggs in larvae or pupa or other insects - young consume tissue of living host ## Tropic structure - keystone species: species has strong effect on community composition 1. First trophic level (primary producers or autotrophs): - plants + other photosynthetic organisms that capture sunlight + convert it to chemical E - use inorganic molecules to build organic molecules - few extreme environments → chemosynthetic bacteria are primary producers) 2. Second trophic level (primary consumers): herbivores that eat plants 3. Third trophic level (secondary consumers): carnivores that feed on herbivores 4. Fourth trophic level (tertiary consumers): carnivores that feed on other carnivores 5. consumers (heterotrophs): acquire energy + nutrients by eating other organisms 6. omnivores: feed at several trophic levels 7. scavengers (detrivores): animals that ingest dead organisms 8. decomposers: small organisms (bacteria + fungi) that feed on dead or dying organic material ## Food chains + webs 1. trophic structure is food chain 2. each link in chain points from food to consumer 3. straight-line food chains → rare in nature 4. food web: set of interconnected food chains with multiple links ## Factors that determine biodiversity 1. disturbance 2. evolutionary age 3. climate 4. immigration rate 5. area extinction effects ## Ecological succession - occurs because species alter habitat + resources in ways that favour other species 1. primary succession: starts on lifeless substrate where no community existed 2. pioneer species: there first 3. climax species: species at end of succession → better competitors + longer life cycle