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Lecture 20 Competition and Predation 1) Review: intertidal zonation 2) Causes of zonation -Physical and biological factors -Temperature and desiccation.

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Presentation on theme: "Lecture 20 Competition and Predation 1) Review: intertidal zonation 2) Causes of zonation -Physical and biological factors -Temperature and desiccation."— Presentation transcript:

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

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

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4 Olympic Peninsula, Washington State

5 Newport Beach, CA

6 Kodiak Island, AK

7 Rio De Janeiro, Brazil

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

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

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11 Causes of Zonation

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

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

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)

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

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17 heat an desiccation stress

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

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

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

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

23 Balanus grows 70% > than Chthamalus Balanus overgrows and undercuts Chthamalus Connell’s Observations:

24 What sets the lower limits for Balanus?

25 Predation Connell (1960s) Predatory Snails - Nucella

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

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

29 Paradigm of Intertidal Zonation:

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

31 Predator Exclusions on Dissipative Shores large predators excluded control

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

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

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35 Growth (mm)


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