Lec 5 positive interactions and communities

True

• D and E are both correct 

• Both A and B are correct, but more info is needed to see if its correct or not 

  • Doesn't say how long they will coexist for 

• C: coexistence if neither is near carrying capacity 

  • Once they do -> better competitor out compete the other one 

• A: predator mediated co-exisnce 

• B: Niche partioning 

• C: short term coexistence 

• D or E: have to say co-existence for the long term 

  • If it does -> D is the only answer 

  • Without: E because it also exists short term co-existence 

    • Once carrying capacity, other things need to be involved (other mechanism) 
      regular disturbance, niche partioning, other spcies,  

What did the old definition of Niche depend on?

• Old: Negative interactions form basis of niches 

• More recent: importance of multaism and commensalism that impact where they can be in space 

What is mutualism?

• when two interacting individuals both experience a net benefit from an interaction (+/+)

• Characteristics

  • More common in harsh environments where species may struggle to persist

    • Struggling to persist -> gain help to stabilize presence in community 

  • By-products benefits - benefits of mutualism outweigh costs of mutualism for both species

    • Cooperation/ mutualism is a byproduct by you directly benefit 

    • Both benefit directly from cooperation 

  • Can involve protection from predators/herbivores/ competitors, or increased access to resources

What is altruism?

• Form of mutualism

• I help you and don't get a direct benefit 

What is reciprocity?

• delayed mutualsim

What is pollination predator protection?

• service mutualism (providing surface) 

What is a common mutualism?

• plant and fungi

• Plants form strong relationships with fungi 

• Fungi give more access to volume of soil so they can draw  

  • Can also mobilize phosphate 

• If lost -> short lived species (terminal branches -> don’t leave descendants) 

  • Lose it when they become carnivorous because they can digest insects instead of from soil 

What is FM fungi?

• Some form symbiotic relationships with plants and algae

• Plants gain access to nutrients and maybe pathogen protection, fungi gain food (carbohydrates)

• Mostly nitrogen and phosphate in soil access 

• Some the fungi protect roots in soil from pathogens (service) 

• Fungi gets carbon from plants 

What are ascomycetes?

• Some form symbiotic relationships with cyanobacteria and green algae (lichens)

• Some are EMF (ectomycorrhizal) à form symbiotic relationships with plant roots

  • Ecto: don’t enter plant cells (surround it) -> give plants nutrients in return for carbohydrates 

What can tightly linked mutualism lead to?

• co-evolution

• Strong direct interactions where they both benefitting 

• Strong evolutionary pressure sources on each-others 

  • Agents of NS on each other -> can cause them to evolve to be better at commensalism (co-evolution) to keep higher fitness 

• Humming bird bills 

  • Modified bills 

  • Converged along with plants as they became flowering plants (they pollinated those plants) 

  • Hummingbirds, moths, bats have strong evolution with angiosperms 

  • Flower shape matches bill shape -> specialists  

• Humming birds can also be generalists 

What is symbioses?

• close, prolonged interaction between two species, often with one species providing habitat for other species to live in

• Symbiosis 

  • Pea aphids have bacteria to help digest food 

  • Get food from whatever the aphid digests 

  • Mutualism so tight 

    • Phylogenetic tree and aphid perfectly match 

      • When the aphid speciated so did the microbe 

      • = vertical transmission 

        • Microbe from your parent (same for humans) 

What are the types of symbioses?

• Types of symbioses

  • One is living on or inside the other 

  • Mutual gut biome is their home 

  • Also be internal parasites 

  • commensalists

what is Obligate mutualism?

• a mutualism in which at least one of the interacting organisms cannot survive without the other organism

  • Ex: obligate for face mites, commensilaist for us 

• Pea aphids form symbioses with Buchnera bacteria Obligate mutualism

  • Aphids need the amino acids provided by Buchnera to survive

  • Buchnera can no longer live on their own – they require host environment to survive

What is Commensalism?

• when one individual benefits from an interaction and the other species neither benefits nor is harmed (+/0)

• Looser bond -> less likely to co-evolve (need strong impact on both species to co-evolve)  

• Cattle move through field -> flying insects fly away -> bird eats them 

  • Easy way to see what food is in the field 

  • Doesn't help the cattle 

What can commensalism lead to?

• Commensalism can lead to mutualism (NS select for mutualism) 

  • Water buffallo: most cattle don’t care 

  • Water evolved to recognize the alarm call form the birds and react to it -> mutualism (gaining information) 

What is facilitation?

• when one species benefits another species indirectly, often through its impact on a third species or on the environment itself.

• Nurse plants

  • In arid habitats, conditions are harsh, making it difficult for seedlings to grow

  • Trees like paloverde, mesquite, ironwood shade the ground, decreasing water loss by evaporation, increasing soil fertility

  • This increases seed germination and seedling survival rates for other plants in the same area

• Nurse plants 

  • Plants that create habitat for baby plants of multiple species 

  • Desert where sun this the ground and soil is dry due to evaporation 

    • Trees shade soil 

      • More water in soil with less evaporation 

      • Lots of baby plants in sun shelter -> increases germination and seedling surving x

What can happen with any relation?

• Facilitation and commensalism 

  • Nurse doesn't care because they are so small 

  • When it becomes larger -> might compete with nurse plant for mycrhoozial interactions and resources 

• Relationships can change in time and space 

• B 

  • Ask teacher if it eating insects they observe escaping ants would not be commensalism because its taking food they could have?  

What are interactions?

• Positive interactions in harsher conditions can become negative

• Soil temperature  

  • Cat tails and forget me not 

  • Cat tails 

    • Soils are anoxic (decomp can use lots of oxygen, and for water logged soils its hard for oxygen to permanent deeper) 

      • Plants roots have high oxygen demands -> can hamper growth in low oxygen level 

    • Can passively transports in oxygen through air spaces in leaves to roots and add oxygen to soil 

      • For own benefit and neighbor can also access it 

  • Forget me nots don’t have availability to move oxygen 

    • Low temp: soil oxygen increased with cattails 

      • Inc in oxygen made forget me nots happier 

    • Soil oxygen did not increase when they were present at high temp 

      • Maybe stressed 

    • Only getting benefit at low soil temp -> context dependent 

• Plants at high altitude 

  • Colder, shorter growing seas, pp of gases lower -> more likely to be mutualism with each other  

  • Move them downhill -> become competition  

What is community?

• interacting populations of different species found in same place/time, interrelationships govern flow of energy and nutrient cycling within community

• Pops found in the same time and space that interact 

What is community structure?

• set of characteristics that shape communities

• Two important descriptors of this are…

  • Species diversity: how many species present (variability)

  • Species composition: who is present (ex: are deer present, specific species)

• •Provides quantitative basis for generation of hypotheses to understand community function

What can impact community structure?

• Direct effects

• Indirect effects

What are direct effects?

• influence of one species on another due to them interacting (predator/prey)

• impact the species directly 

What are indirect effects?

• influence of one species on another through intermediaries

  • predators impact one another because they feed on same prey

• Us interacting occurs in a community where other species is something they both interact with 

• Ex: harvest seals because they were competing with them for fish 

  • Found out that fisherman and seals both consume same number of fish 

  • Remove seals -> fisherman harvest went down because seals had direct negative effect on fish but they had positive direct affects as well by eating their predators 

What is easier to measure and predict?

• Direct effects are often easier to measure and predict,

• but often community food webs do not react in predictable manner due to indirect effects

• Direct effects can be measured easily 

• Indirect harder: through removal experiments 

  • Make communities act in different directions and cause harm 

Examples of species interactions?

• Snow geese and lemmgins both eat grasses 

  • Could have direct negative effect 

• Artic fox eats both, snowy owls only eat lemmings 

  • Graph shows indirect and direct relations 

  • Lemmings positive indirect with snow geese p

What is trophic cascade?

• when the rate of consumption at one trophic level results in a change of species abundance / composition at lower trophic levels (causes a cascade)

• Predators and prey can also have preds or their own and so on 

• Predation at higher level that impact lower trophic levels 

• Predation on herb can have positive indreict effect on basal because less herbs to eaet them 

What happens in apex predator population changes?

• changes in apex predator pop abundance → cascading effects that reach food webs

• Killing apex predators 

• Sharks 

  • Second degree consumer -> 1 degree etc can impact nutrients 

    • Producers add nutrients to food web 

  • Killing sharks 

• Prey of sharks going up -> scallops (filter feeders) go down 

  • Changing the amnt of things in water column by inc secondary consumers? 

What is trophic facilitation?

• when a consumer is indirectly helped by a positive interaction between its prey and another species

• Two species that interact directly in a way that benefits them (commen or mutualism) that benefit the predator 

  • B1 Support higher biomass in B2 -> benefit predator 

What is the relationship between aphids and Juncus and Iva?

• Commensaltic relationship (trophic facilitation)

  • Juncus shades soil and salt buildup, and arinchma that adds oil 

  • Iva grows more biomass -> aphids eat Iva -> higher colony of aphids 

  • Aphids benefit indrecity form impact of juncus on IVA 

  • Presence of junca 

    • Help support higher predation and grow them 

    • More positive effect than negative (commensalism) 

What about cats?

• indirect effects and be unpredictable

• Cats Good hunters → kills birds and reptiles

• Efforts to eradicate them from islands often lead to INCREASES in native wildlife losses → WHY?

  • Remove cats from islands -> can lead to further loss of life 

    • Controls rats that is another invasive species -> remove cats -> remove control of rats that kept under carrying capacity 

• feral cats control invasive rats pop

• remove cats → rats experience ecological release and grow exp → more native species killed by rats because they compete with them for food

  • cats direclty kill native species, but indirectly facilitate them by controlling rat population

• C

What is a dominant species?

• species that have a large effect on community because they are more numerous or have highest biomass within community

• ex: deer have large impact when in high numbers

  • Deer are often abundant, especially in areas without wolves

  • Deer graze heavily on young trees → large impact on forests where deer are in high numbers because reduces tree recruitment rates

  • Deer are also be important seed dispersers for many plants

  • Each individual deer has a relatively small effect on community, but a deer population can have a large impact when it is very large

• Large impact because there's lots of them 

  • Little biomass -> little impact 

• Deer: lots of deer's disperse seeds, eat baby trees 

• Wolves removed -> deer's impact communities negatively 

What are keystone species"?

• species that affect other members of community in ways that are disproportionate to its abundance / biomass

• one indiv → large impact

• Sea Otters – keep sea urchin numbers in check, which maintains kelp beds

Ecosystem engineers?

• species that actively shape their physical environment in ways that create habitat for for other species

• Hippos – feed on terrestrial vegetation and defecate in rivers, moving nutrients from terrestrial ecosystem into aquatic one

• Beavers – build dams that create pond/lake habitats

Foundational Species?

• species that provide structural habitat for other species

• Trees, coral reefs, sea kelp, mangrove trees are all foundational species because they provide physical structure that other species can live on/in

How are beavers ecosystem engineeers?

• Beaver lodges block flow of water from surroundings to wetlands → makes pond that drowns all trees downstream of the lodges → creates homes for cavity-nesting birds, food for insects, and fungi

How does facilitation work with the types of species?

• Facilitation can include different types of positive interactions

• Foundational species

  • Species that provide structural habitat for others to live on/in

  • E.g. trees, coral reefs, kelp, mangroves

• Ecosystem engineers

  • Species that modify the environment in ways that impact the biodiversity of the region

  • Can involve creating suitable habitat for species, creating habitat that is less suitable, or both!

  • Creation of habitats or fate of nutrients (hipos and beavers) 

  • Nutrients: shape community features because it shapes what kind of primary production can take place 

• D (impact due to high numbers -> Dominant species)