Slide 1

Lecture 20 Competition and Predation 1) Review: intertidal zonation 2) Causes of zonation -Physical and biological factors -Temperature and desiccation (Foster) -Competition and predation (Connell) 3) Competition on sediment shores -Deposit feeders (Levinton, Posey) 4) Keystone species -Pisaster

Slide 2

Intertidal Zonation: -Subclassifcation of ecosystems -Smaller zones with unique physical characteristics -Unique habitat that favors particular species

Slide 3

Slide 4

Olympic Peninsula, Washington State

Slide 5

Newport Beach, CA

Slide 6

Kodiak Island, AK

Slide 7

Rio De Janeiro, Brazil

Slide 8

Atlantic Coast North America Large kelps (Laminaria) Red algae Small kelps, mussels Barnacles, predatory snails Microalgae and grazers: herbivorous snails

Slide 9

Large kelps, Small kelps, mussels Barnacles, predatory snails Microalgae and grazers: herbivorous snails Pacific Coast North America Red algae

Slide 10

Slide 11

Causes of Zonation

Slide 12

water Frank 1965 Observation High shore organisms: exoskeletons Hypothesis Desiccation sets upper tidal limits Prediction Dripping water will cause increase in upper tidal limits

Slide 13

Chthamalus stellatus Balanus balanoides Balanus crenatus high-shore intertidal mid-shore intertidal subtidal Foster, 1960-70s

Slide 14

Temperature At 100% humidity: Mean lethal time (hours) lethal temperature (C) high-shore species (Chthamalus) mid-shore species (Balanus balanoides) subtidal species (Balanus crenatus)

Slide 15

Desiccation Chthamalus (high-shore) S. balanoides (mid-shore) B. crenatus (subtidal) At 17-20C, 0% humidity:

Slide 16

Slide 17

heat an desiccation stress

Slide 18

Balanus balanoides low shore Chthamalus stellatus high shore Species Interactions: Competition

Slide 19

Biological factors: Larval settlement Larvae tend to settle on tidal heights based on environmental cues Barnacles: Gregarious settlement Barnacle cyprid larva

Slide 20

Slide 21

Connell (1961) Chthamalus Balanus Upper limits of Both set by physical stress What sets the lower limits of Chthamalus?

Slide 22

Bottom of Chthamalus zone Top of Chthamalus zone Experimental removal of Balanus

Slide 23

Balanus grows 70% > than Chthamalus Balanus overgrows and undercuts Chthamalus Connells Observations:

Slide 24

What sets the lower limits for Balanus?

Slide 25

Predation Connell (1960s) Predatory Snails - Nucella

Slide 26

Slide 27

Low intertidal: transplanted Balanus below their natural lower limit Predation: caging experiments Connell (1961)

Slide 28

Temperature and desiccation prevent both Chthamalus and Balanus from living at higher levels Competition from Balanus prevents Chthamalus from inhabiting the middle zone Predation by snails sets the lower limits of the distribution of Balanus Balanus zone Chthamalus zone

Slide 29

Paradigm of Intertidal Zonation:

Slide 30

Sediment vs Rocky Shores High heat and desiccation stress Stable substrate Sedentary lifestyles Resident predators Benthic macroalgae, microalgae Rocky Shores Less heat and desicc stress Unstable substrate No SSOs Transient and mobile predators Microalgae, drift macroalgae Sediment Shores

Slide 31

Predator Exclusions on Dissipative Shores large predators excluded control

Slide 32

Hargrave (1970) Trophic Structure of Mudflats Deposit feeders Heterotrophic bacteria POM Benthic Algae

Slide 33

Competition for Food on Sediment Shores Jeff Levinton (1972) American Naturalist Suspension Feeders: Deposit Feeders:

Slide 34

Slide 35

Growth (mm)