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Biology 205Ecology and Adaptation

Mutualism,Species Abundance, and DiversityDr. Erik D. Davenport

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Outline (chapter 15-16)

Introduction of mutualism.– Plant Mutualisms– Coral Mutualisms

What is community. Species Abundance ----Lognormal Distribution Species Diversity Environmental Complexity --- Niches Disturbance and Diversity

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Introduction

Mutualism: Interactions between individuals of different species that benefit both partners.

– Facultative Mutualism occurs when a species can live without its mutualistic partner.

– Obligate Mutualism occurs when a species is dependent on a mutualistic relationship.

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Concept1: plant mutualisms

Plants benefit from mutualistic partnerships with a wide variety of bacteria, fungi, and

animals.

Mycorrhizae: the symbiotic association of the a fungus with the roots of a seed plant

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Mycorrhizae and Plant Water Balance

Hardie suggested mycorrhizal fungi improve water relations by providing more extensive contact with moisture in rooting zone and providing extra area for water absorption.

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Mycorrhizae and Plant Water Balance

Allen and Allen studied water relations of grass Agropyron smithii. – Plants with mycorrhizae maintained higher leaf

water potentials.– Plants with greater access to phosphorus may

develop roots that are more efficient at extracting and conducting water.

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Nutrient Availability

Fungal partner received an equal or greater quantity of photosynthetic product in trade for low quantity of nutrients.

Results suggested mycorrhizal fungi from unfertilized soils supplied plants with more nutrients.

Plants able to invest more energy in above-ground photosynthetic material.

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plant mutualisms -- Mycorrhizae

Benefits for plants: Plants receive more water and nutrients.

Benefits for Fungus: Fungus receive photosynthetic products (sugars) from plants

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Coral Mutualisms

Zooxanthallae and Corals– Zooxzanthallae is one type of phytoplankton

(dinoflagellates) live within coral tissues.– It receives nutrient from coral. – In return, coral receives organic compounds

synthesized by zooxanthallae during photosynthesis.

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Coral Mutualisms

Corals also control rate of zooxanthallae population growth and density by influencing organic matter secretion.

Main zooxanthallae benefit appears to be access to higher nutrient levels, especially N and P.

Uptakes ammonium excreted by coral.

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Coral Protection Mutualism

Glynn found 13 coral species protected by crustacean mutualists.

Crustacean mutualists substantially improved chances coral will avoid attack by sea stars.

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Community(what is population???)

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Introduction

Community: Association of interacting species (population) inhabiting some defined area.

Community Structure includes attributes such as number of species, relative species abundance, and species diversity.

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Pattern of Species Abundance

There are regularities in the relative abundance of species in communities that hold irregardless of the ecosystem.

Most species are moderately abundant; few are very abundant, or extremely rare.

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Lognormal Distribution

Preston graphed abundance of species in collections as frequency distributions.– Lognormal Distributions– Bell-shaped curves.– In most lognormal distributions, only portion of

bell-shaped curve is apparent.– Sample size has large effect.– Significant effort to capture rare species.

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Lognormal Distribution

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Species Diversity

Which one do you think that has the higher diversity? Why?

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Species Diversity!!!!

Two factors define species diversity:– Species Richness

Number of species in the community.– Species Evenness

Relative abundance of species.

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Quantitative Index of Species Diversity (you don’t need to remember the

equation)

Shannon Wiener Index:

H’ = Value of SW diversity index. Pi = Proportion of the ith species. Loge = Natural logarithm of pi. s = Number of species in community.

ie

s

i

i ppH log'1

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Rank Abundance Curves

Can also portray relative abundance and species diversity within a community by plotting relative abundance of species against their rank in abundance.

Greater evenness indicated by lower slope.

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Rank Abundance Curves

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Environmental Complexity

In general, species diversity increases with environmental complexity or heterogeneity. why???

– Higher environmental complexity will introduce a more diversified environments -- more niches

– More niches higher species diversity

Many studies have shown positive relationship between environmental complexity and species diversity.

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Environmental Complexity

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Niches and Diversity of Algae and Plants

Hutchinson:– Phytoplankton communities present a paradox

because they live in relatively simple environments and compete for the same nutrients, yet many species coexist without competitive exclusion.

– Environmental complexity may account for significant portion of the diversity.

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Niches and Diversity of Algae and Plants

Algal niches are defined by their nutrient requirements.

Difference algae species require different type of nutrients

Tilman found coexistence of freshwater diatoms depended upon ratio of silicate and phosphate.– Found conditions allowing coexistence.– Diatoms held different trophic niches.– Thus different diatoms would dominate different areas.

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Algal and Plant Species Diversity and Increased Nutrient Availability

Repeatedly observed negative relationship between nutrient availability and algal and plant species diversity.

What is eutrophication? Adding nutrients to water or soils generally

reduces diversity of plants and algae. Why??? Reduces number of limiting nutrients.

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Disturbance and Diversity

Disturbance difficult to define as it involves departure from “average conditions.”– Average conditions may involve substantial

variation. Sousa defined disturbance:

– Discrete, punctuated, killing, displacement, or damaging of one or more individuals that directly or indirectly creates an opportunity for new individuals to be established.

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Disturbance and Diversity

White and Pickett defined disturbance:– Any relatively discrete event in time that disrupts

ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment.

– Two major characteristics: Frequency Intensity

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Intermediate Disturbance Hypothesis

Connell proposed disturbance is a prevalent feature that significantly influences community diversity.– Proposed both high and low levels of disturbance

would reduce diversity.– Intermediate levels promote higher diversity.– Sufficient time between disturbances allows wide

variety of species to colonize, but not long enough to allow competitive exclusion.

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Disturbance and Diversity in the Intertidal Zone