Session 6: Functional groups

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Functional group concept

Whats the relationship between species diversity and functional richness

Functional effect or functional response?

Defining functional groups

Body size

Sediment stabilisers-destabilisers

Consideration of habitat structure

Are species vertically separated?

YES

X-ray used to look at bivalves (instead of sieves)

→ segregated by depth

How vertical separation affect what species do? with example

Similar depths feeders have more competition

e.g.

Saxidomus and Tresus are more dominant filter feeders

The growth of Sanguinolaria was reduced by 80% in their presence

but unaffected by Protothaca (it is also not affected by others)

Functional feeding groups

Are feeding groups spatially segregated?: The food availability hypothesis suggest

Suggest:

• Sandy sediments were dominated by suspension feeders

• Muddy sediments were dominated by deposit feeders

• by food avaliability

Are feeding groups spatially segregated?:

3 reasons that The food availability hypothesis is incorrect

(i) more organics in water column above mud, but still no suspension feeders

(ii) boundaries between suspension feeding and deposit feeding were often too sharp to reflect food supply gradients,

(iii) hard substrata (e.g. rocks) in otherwise muddy sediments were not necessarily covered in suspension feeders.

Does one feeding group really replace another?

Do deposit feeders increase erosion?

Does sediment resuspension benefit suspension feeders?

The Trophic Group Amensalism Hypothesis

How applicable is the trophic group amensalism hypothesis?

3 Trophic groups

Detritivores

Carnivores

Herbivores

6 subcategories that capture detritus WITHOUT hard mouthparts

• pseudopodial feeders (e.g. Foraminifera)

• filter feeders with cilia (e.g. Porifera)

• tentaculate feeders (e.g. holothurians)

• proboscoidal feeders (e.g. sipunculids)

• tube feet (e.g. some echinoderms)

• nematocysts (e.g. jellyfish and hydroids)

4 subcategories that capture detritus with hard mouthparts

• radula (e.g. molluscs)

• mandibles or teeth (e.g. priapulids)

• chitinous limbs (e.g. crustaceans)

• calcareous tooth jaws (e.g. echinoids)

Extension of trophic groups

Bioturbation: 7 types of bioturbation

A, epifaunal;

B, surficial modifiers;

C, biodiffusers;

D, gallery biodiffusers;

E, upward conveyors;

F, downward conveyors;

G, regenerators

Example for changing feeding mode on impacting bioturbation

As Species can simultaneously have multiple functional designations

polychaete Cirriformia grandis is a urficial modifier and an epifaunal detritivore

….

Combining feeding, motility and burrowing

Bioturbation potential

Biological Trait Analysis

Are the traits relevant in looking at nutrient etc.

→ lacking evidence

Which functional group approach should we use? Why?

Depends and need justification when using one

What does a functional group need to be?

Unlikely to be a single universal solution as

• Based on common attributes rather than
  phylogenetic relationships

• Incorporate interactions between
  organisms and their environment

• relevant to ecosystem function/property
  of interest

→ need to be supported by empirical evidence and accompanied by caveats (limitations,
scale, context etc.)