Ecology B.Species Interactions 1.Intraspecific competition Ex – Competition for algae by sea urchins Ex – Competition for shells by hermit crabs 2.Interspecies

EcologyB. Species Interactions

1. Intraspecific competition• Ex – Competition for algae by sea urchins

• Ex – Competition for shells by hermit crabs

2. Interspecies competition


2. Interspecific competition – Competitive exclusion


3. Predation• Natural selection favors increased predation efficiency• Predators can control prey populations (Top-down)

• Reduce competition/competitive exclusion• Prey can control predator populations (Bottom-up)

• Prey = food• Some prey have evolved defense mechanisms

• Ex – Spines in plankton• Ex – Poisonous chemicals in algae and mollusks

• Some defenses are inducible• Ex – Barnacles grow upright when predatory snails absent and horizontally when snails present• Ex – Algae produce more bad-tasting chemicals after being damaged

• Coevolution – Evolutionary “arms race”


3. Predation• Natural selection favors increased predation efficiency

• Predators can control prey populations (Top-down)

• Reduce competition/competitive exclusion

• Prey can control predator populations (Bottom-up)

• Prey = food


3. Predation• Some prey have evolved defense mechanisms

• Ex – Spines in plankton

• Ex – Poisonous chemicals in algae and mollusks

• Some defenses are inducible

• Ex – Barnacles grow upright when predatory snails absent and horizontally when snails present

• Ex – Algae produce more bad-tasting chemicals after being damaged

• Coevolution – Evolutionary “arms race”


4. Symbiosis• Relationship between host and symbiont

a. Commensalism• One partner benefits, other unaffected• Ex – Barnacles living on whale

b. Parasitism• One partner benefits at expense of other• Common in marine environment• Ex – Tapeworm in whale

c. Mutualism• Both partners benefit• Ex – Cleaner wrasses and shrimps on coral reefs• Ex – Anemonefishes and anemones

EcologyC. Trophic Structures

• Energy and matter flow through ecosystems can be described through trophic relationships

• Relationships between producers and consumers = food chain


• Food chains are often simplistic – alternative is a food web


• Food chains are often simplistic – alternative is a food web


• Energy transfer between trophic levels not 100% efficient• Matter consumed by metabolism

• Energy released as heat

• Matter released as waste

• Transfer efficiency ~ 10% (5-20%)


• Energy transfer can be illustrated as pyramid of energy• Higher levels contain progressively less energy


• Energy transfer can be illustrated as pyramid of energy• Higher levels contain progressively less energy


• Decomposers – break down waste products

Marine ResourcesA. Fisheries

• Seafood is ~1% of all food eaten worldwide

• Seafood especially important in poor coastal nations with low protein availability

• World seafood catch stabilized by late 1980s







1. Clupeoid fishes• Herrings, sardines, anchovies, menhadens, shads• Feed on plankton (use gill rakers)• Form large schools over continental shelves and in upwelling zones

• Caught with purse seines• Industrial fisheries

- Fish meal (protein supplement in animal feed)

- Fish oil (margarine, cosmetics, paint)

- Fish flour (protein supplement for humans)

- Fertilizers

- Pet food


1. Clupeoid fishes



2. Cods and related fishes• Cods, pollock, haddock, hakes, whiting

• Demersal and benthopelagic cold-water fishes

• Caught with bottom trawls

• Grand Banks (Newfoundland), Georges Bank (New England) and North Sea supported extensive cod fisheries until 1992, 1994, and 2001, respectively

• Cod populations crashed; catches plummeted

• Ex – North Sea catch

• 1971 – 277,000 tonnes

• 2001 – 59,000 tonnes




3. Tunas• Skipjack, yellowfin, albacore, bigeye, bluefin

• Primarily eaten in affluent countries

• Can be very expensive (up to $40,000 for a choice bluefin in Tokyo)

• Highly migratory species

• Caught with purse seines, longlines, gill nets, rod and reel

• Often associate with floating objects, dolphin schools

• Juveniles caught in purse seines may be finished in net pens (aquaculture)


3. Tunas



4. Other species• Flatfishes, rockfishes, mackerels, salmon

• Mostly coastal

• Threatened by coastal pollution, damming of rivers (salmon), overfishing

• Flatfishes and rockfishes harvested extensively in US

• Salmon farmed heavily in Canada, Chile

• Non-finfish

• Squid, octopus

• Clams, oysters, scallops

• Crabs, lobsters

• Sea urchin, sea cucumber

• Barnacles, jellyfish

• Sea turtles, seals, whales


5. Fishery Yields


5. Fishery Yields

• Overfishing leads to1) Stock depletion

2) Reduced catch rate

3) Capture of smaller individuals

4) Unsustainable harvest

• Biological – Can’t reproduce fast enough

• Economic – Can’t catch enough to make a profit


5. Fishery Yields

Documents

Ecology B.Species Interactions 1.Intraspecific competition Ex – Competition for algae by sea urchins Ex – Competition for shells by hermit crabs 2.Interspecies