23/24 Flashcards
primary producers
plants
primary consumers
herbivores
secondary consumers
carnivores who eat herbivores
tertiary consumers
carnivores who eat secondary consumers (predators)
decomposers
eat dead organic matter
what does the pyramid shape represent?
decreasing biomass in higher trophic levels
describe indirect effects in food webs/chains and give an example
- one species alters the effect that another species has on a third
- eg exploitative or scramble competition, if the contested resource is a species
trophic cascades: HSS
interactions between two trophic levels cascade to a third trophic level
why is the world green?
- Hairston, Smith, Slobodkin (1960) proposed the green world hypothesis
- states that carnivores keep down herbivores so herbivores don’t limit plant growth
how is the green world hypothesis an example of an indirect effect?
one trophic level exerts influence on a second by affecting a third
top down control
abundances kept low because of predation
- experimental test = predator removal
bottom-up control
abundances kept low because of resource limitation
- experimental test = resource addition
solid lines for trophic cascades
direct effects
dashed lines for trophic cascades
indirect effects
compare indirect and direct effects
- indirect effects can be as strong as direct effects
- outcomes are not fundamentally predictable; this depends on interaction strengths
- experiments are needed (perhaps long term)
where does much biodiversity reside?
plants and insects
why are there so many species of insects and plants?
- Coevolution
- Niche specialization
- Rapid reproductive cycles
- Habitat diversity
- Polyploidy in plants
- Metamorphosis in insects
- Geographic and climatic stability
- High mutation and adaptation rates
difficulties of herbivory as opposed to carnivore
- animal tissues are easy to convert into animal tissues
- plant tissues are hard to convert into animal tissues
3 difficulties of plant tissues
- cellulose and lignin are tough and indigestible without microbial symbionts
- plant tissues are heavily defended against herbivores
- coevolutionary race between plants and insect herbivores is responsible for much of biodiversity: specialisation is common
example of plant defences against herbivores
milkweeds exude distasteful white sap if damaged
- most generalist insects can’t eat milkweeds, but specialists can evade defences
- milkweed-feeding specialist monarch butterfly larva cut leaf midrib to reduce sap pressure before eating
- caterpillars don’t detoxify the poison, but sequester it in their cuticle, making themselves poisonous and distasteful
brightly coloured insects
- frequently toxic
- warning coloration
plant-herbivore interactions as an arms race
- plants evolve toxins to reduce herbivory; insects evolve detoxification or other mechanisms to overcome plant defences
- many types of secondary chemicals (esp alkaloids) often deter generalist herbivores
- no plant species is toxic enough to escape from specialist herbivores
- specialist insects may evolve to use defence chemicals as feeding stimulants or defence compounds
result: escalation, arms race!
why do we think plants taste ok?
our food crops have been selected for low toxicity
how are plant defensive compounds important to humans?
- many plant secondary chemicals have diverse, potent biological activities
- some alkaloids are important to us
examples of useful alkaloids for humans
coffee - caffeine
coca - cocaine
tobacco - nicotine
opium poppy - morphine
in what ways are challenges and solutions different for vertebrate herbivores?
- Many insects complete development on a single, often well-defended plant; they must overcome plant defences
- Vertebrate grazers often eat some plant tissue, and then move on to another plant
- Vertebrate herbivores often select mixed diets containing foods processed by different
detoxification pathways, thereby avoiding high doses of any one toxin - Some detoxification by microbes in fermenting chambers
rumen
foregut
cecum
hindgut
what produces unlimited diversification?
physical environment isn’t complex enough to produce extraordinary species diversity
interactions with other organisms do this
why do plants around a pond with fish get better pollination and bees?
there are fewer dragonflies
two examples of complex networks of species interactions in ecological communities
- parasite-herbivore-plant network (Costa Rica)
- plant-pollinator network (Greenland)
why do lizards benefit plants?
because of unequal interaction strengths:
- effect of lizards on spiders is week
- effect of lizards on herbivores is strong
- lizards reinforce the effect of spiders
lizards eat
spiders and herbivores
spiders eat
herbivores
what do Anolis lizards eat?
spiders and beetles
Spiller and Schoener 1992
replicate Caribbean islands; remove Anolis lizards
major threats to biodiversity
- habitat destruction
- overexploitation
- invasive species
- pollution
- climate change
often have synergistic effects
what four things can result from environmental change?
acclimation, adaptation, range shifts or extinction
give 4 examples of changes to the environment due to humans
- ice disappearing
- forests cut down
- primates sold as pets or bushmeat
- mercury put in rivers
- microplastics
effects of increasing atmospheric CO2 levels in the last century
- human activities adding more CO2
- intensifies greenhouse effect and causes global warming
- global temperature has increased dramatically
how is climate changing other than temperature?
- circulation patterns are changing: Hadley cells get stronger and therefore larger, causing desert belts shifting poleward beyond 30 degrees
- extreme weather events becoming more frequent
what happens to organisms as the climate changes?
acclimatisation through phenotypic plasticity
adaptation to new conditions
range shift migration to suitable conditions
extirpation, which is global or local extinction
acclimation
Early or gradual exposure to environmental stress can reduce its negative impacts
- Porcelain crabs (Petrolisthes) acclimated
to cold temperatures function better at colder temperatures
- But acclimation to warm temperatures increases high-temperature tolerance only minimally
give an example of how climate change is more than just the direct effects of warming
Snowshoe hares (Lepus Americans) are white in winter and brown in summer
Coat colour is important for reducing predation, and white animals are conspicuous against a snowless background
Mills et Al.
- studied snowshoe hares in western Montana over 3 consecutive winters
- radio-collared hares and performed weekly measurements of coat colour and snow around each hair
- wanted to determine whether there I sufficient, current plasticity in the initiation or rate of coat colour change to reduce mismatch and respond to changes in snow cover
Mills et Al. results
- it is getting cooler later in the fall and warmer earlier in spring
- in general, snow is arriving later and leaving earlier
- there is little variation in fall coat change; there is more variation in spring coat change
so, will plasticity alone in coat colour change able to respond to changes in conditions?
No, there is not enough plasticity to avoid mismatches
- projections of future snow duration show there will be greater mismatch between snowshoe hare coat colour and its background
how is coat colour mismatch predicted to affect hare population growth?
predicted to slow it
so, will hares adapt?
open question; depends on the amount and type of genetic variation underlying the timing of coat colour change
range shifts
- species moving polewards
- also up mountains
give an example of an animal that can’t go up mountains
pikas; death zone at low altitude
the Great Basin
many small mountain ranges, green ‘sky islands’ in a matrix of desert
are pikas threatened by climate change?
The elevational range of American pikas in the Great Basin is getting smaller
- Sites where pikas have gone locally extinct often had temperatures above 26°C, which can be lethal to pikas (if they cannot behaviourally thermoregulate)
- The American pika was under consideration to be listed as an endangered species in the US (but the US ultimately decided against it)
- On the other hand, American pika populations in the Rocky Mountains and elsewhere appear to be healthy
(Smith et al. 2020)
- In Canada, the Collared pika (which lives in the Yukon, Northwest Territories, and BC) is federally designed as a species of “Special Concern’
example of landscapes defeating migrations
Pronghorns can run but not jump. Whole herds have been killed at fences in the winter
is extinction reversible
no
most extinction models ignore
many factors thought to be important in determining future extinction risks such as species interactions, dispersal differences, evolution
