Download Generalized food web showing Consumer

Generalized food web showing Consumer functional groups
Dissolved nutrients
Sedimentation and
Microbial colonization
Microdetritus
Macrodetritus
Living plants and algae
Macro
Micro
Sedimentation and
Microbial colonization
Primary production
Primary productionFeces
Macrodetritivores
(Shredders)
Microdetritivores
(Filterers, deposit-feeders)
Macroherbivores
Microherbivores
(Engulfers, grazers, piercers)
Primary consumers
Secondary and tertiary consumers
Carnivores
Carcasses
Scavengers
(Engulfers, fluid feeders)
Consumer functional groups in an offshore lake community
Microproducers—lake phytoplankton, diatoms, green algae, cyanobacteria etc.
Macroproducers—none
Primary consumers
Microherbivores—rotifers, cladocerans, copepods
in fishless lakes, Notostraca, anostraca
Macroherbivores—none
Microdetrivores—chironomid larvae, amphipods, burrowing mayfly larvae,
Macrodetrivores—none
Secondary consumers—mysis, large anostraca, chaoborid larvae
small fish eg smelts, alewife, ciscoes, whitefish, sculpins
stickleback, small perch, sunfish, small salmonids, shiners etc.
many ducks
Tertiary consumers—large salmonids, burbot, walleye, loons, mergansers
Scavengers--leeches
Consumer functional groups in a littoral community
Microproducers—epiphytes, benthic algae.
Macroproducers—submerged, floating leaved, and emergent macrophytes
Primary consumers
Microherbivores—rotifers, chydorid cladocerans, copepods, chironomid and
mayfly larvae, snails, clams, minnows
Macroherbivores—lepidoptera
Microdetrivores—chironomid larvae, amphipods, mayfly larvae,
Macrodetrivores—large amphipods, crayfish, caddisfly larvae
Secondary consumers—odonata, megaloptera, coleoptera larvae
small fish eg stickleback, mid-size perch, sunfish, small salmonids,
many ducks.
Tertiary consumers—pike, bass, large perch, fish eating ducks
Scavengers--leeches
Consumer functional groups in a cold stream community
Microproducers— benthic algae.
Macroproducers—none
Primary consumers
Microherbivores—bdelloid rotifers, chydorid cladocerans, copepods,
chironomid, mayfly, stonefly, caddisfly larvae minnows
Macroherbivores—none
Microdetrivores—chironomid larvae, amphipods, mayfly larvae,stoneflies,
caddisflies
Macrodetrivores—leaf shredding caddisflies, stoneflies, amphipods, and
crayfish
Secondary consumers—predatory stoneflies, megaloptera, coleoptera larvae
small fish eg minnows, small and mid-size trout and whitefish
Tertiary consumers—bull trout, fish eating ducks
Scavengers--leeches
Relationships between fish predators and prey
Bottom up
•Richer systems have higher productivity at all trophic levels
•Enrichment usually increases the biomass of the top
trophic level in the web.
Top down
•Predators usually reduce the biomass of their prey
•And cause changes in the structure of prey communities
•Lake Michigan example
Bottom-up Fish biomass dependent on nutrient loading
Reductions in fish biomass usually accompany reductions in nutrient loading
Study by Cooper and
Power on Top down
effects in a California
stream
During dry summer the
stream becomes a series
of isolated pools
No large fish in the
pool—algae very
abundant
Large trout and/or large
roach—algae very
scarce
Illustrates an effect
known as the top-down
cascade
•The bottom up relationship is well known in aquaculture where enrichment with
fertilizers and/or fish food is standard practice.
•Enrichment can produce fish yields that are orders of magnitude higher than those
normally found in natural ecosystems.
Top-down effects
In addition to reducing prey biomass, predators selectively
remove vulnerable prey, and make it possible for species and
varieties that have better defense mechanisms to win out
over faster growing competitors that lack defenses.
Prey defense mechanisms
•Reduced detectability
Smaller size, transparency, less turbulence
•Defensive behaviour
Vertical migration and night time activity, and avoidance
responses
•Unpalatability
Spines, toxicity
•Altered life-cycle
Diapause and speeding up life-history
Small size can be an effective defense
Effects on size structure of
prey communities
Hrbacek
Brooks and Dodson
•Generally in lakes where
zooplanktivorous fish are
the top trophic level there is
a reduced zooplankton
biomass and a shift in
community compositon
toward smaller species and
species with more effective
defenses
•Similar effects have been
noted in benthic
invertebrate communities.
Why do large herbivorous
zooplankton dominate
communities when there are no
zooplanktivores?
The size efficiency
hypothesis
Which Daphnia can deplete its
food supply the most and still
survive on it?
Why are larger Daphnia more
efficient than smaller Daphnia at
filtering even tiny algae?
Reduced visibility/ less pigmentation also works
In fishless lakes zooplankton are strongly pigmented,
mostly with carotenoid pigments that they obtain from
algae
In lakes with zooplanktivorous fish, zooplankton are
usually nearly transparent and thus very hard for fish to
see
Why do you think that pigmented zooplankton species and
varieties win out over transparent ones in fishless lakes?
Defensive behaviour
In fishless lakes many invertebrates swim about freely in
the water column of both lakes and streams during the
daytime
Where fish are present, they usually confine such
behaviour to the night hours and hide in the bottom during
the day.
Effect of brook trout on the drift response of benthic invertebrates
response = drift density (#/m3) / abundance (#/m2)
no fish
0.030
fish (0.5/m2)
Drift response
0.025
0.020
0.015
0.010
0.005
09-10
13-14
16-17
18-19
Time of day
20-21
21-22
23-24
•In completely fishless streams there is usually no difference between day and night
drift of invertebrates, but where drift feeding fish are present there is usually a sharp
increase in drift at night.
•The differences seen here (fish/no fish) are a result of consumption depleting the #/m3
of drifting inverts.
Drift net in Epinette Creek
Invertebrates that commonly occur in the drift
Some common mayfly
larvae (Ephemeroptera)
Net-spinning caddis larvae
(Trichoptera)
The effect of zooplanktivorous fish onvertical migration of herbivorous zooplankton
McPeek’s studies on damselflies in littoral
Damselflies in fishless lakes are preyed
on heavily by dragonflies
The species that live in lakes with fish
usually respond to a nearby predator by
remaining motionless
The species that live in lakes without fish
respond to predators by rapidly moving
a short distance.
Both of these types of responses work
well against the type of predator for
which they were evolved, but not against
novel predators.
Spines and other extensions of the body
are a good defense against
zooplanktivorous fish
Daphnia with and without helments
Unpalatibility: predators don’t like spines
Sticklebacks in fishless lakes have much smaller spines and much fewer
Armoured plates
Sunfish have both spines and deep body shape that can exceed most predator’s
gape..
As a result, most pumpkinseeds older than 1 or 2 years are rarely preyed upon by
pike or bass.
Gelationous coat produced by
Holopedium makes them less
palatable to fish predators
Changing the life cycle can help minimize predation impact
Daphnia often produce resting or
ephippial eggs in response to heavy
predation
Epphipial eggs are produced from
sexual reproduction and are packaged
using the carapace covering of the
brood pouch
Resting eggs are often produced by
rotifers in response to heavy predation