3 Ecological and Evolutionary Principles

Notes for Marine Biology: Function, Biodiversity,

Ecologyby Jeffrey S. Levinton

©Jeffrey S. Levinton 2001

The Ecological Hierarchy

• Biosphere

• Ecosystem

• Community

• Population

• Individual

Ecological Processes

• Competition

• Predation

• Disturbance

• Parasitism

• Larval Dispersal

• Facilitation

Interactions Between Individuals

• +- Territoriality

• +- Predation

• + - Parasitism

• ++ Mutualism

• + 0 Commensalism

PREDATION TYPES:

Stationary:e.g., anemones

Mobile: (a) sit and wait and attack e.g., (b) pursuite.g., Shark

OVEREXPLOITATION - prey population collapse, occasional predator-prey cycles

PREY ESCAPE(a) rapid recovery rate(b) defenses(c) predators limited by other factors (e.g., octopus by den sites)(d) refuges (space, time)

Effects of Predation

Predation Example: Stationary Predator Anthopleura xanthogrammica, anemone living in tide pools of Pacific coast. Feeds on larger invertebrates that fall into its tentacles, such as mussels.

Crypsis: A marine flatfish with chromatophores that allows it to match its sedimentary background (fish outlined with arrows)

Inducible defenses

A bryozoan makes spines when placed in contact with a predatory nudibranch.

A hydrozoan, Hydractinia, produces defense stolons armed with nematocysts when in contact with another colony.

Inducible Defense: The conical (right) and bent (left) forms of the acorn barnacle Chthamalus anisopoma. The animal develops the bent form if predatory snails are present.

Inducible Defense 2: Often has a cost. Barnacle with bent form does not feed as well. Therefore, it is a good strategy to make the defense optional.

Escape behavior: The bivalve Lima hians can swim from predators by rapidly clapping its valves and expelling water in jets through the hinge. It also has mantle tentacles that secrete a sticky distasteful material that discourages predators.

Optimal Predator Models

• Diet breadth - food scarce --> increase breadth

Optimal Predator Models 2

Time spent in a patch - greater the distance between patches --> spend more time in a given patch

Optimal Predator Models 3

Optimal size of prey --> intermediate is usually preferred, yields the most food per unit time (larger prey good in reward but takes relatively long to eat, smaller prey fast to east but food per prey item is small)

Energy reward of a mussel as function of size

Preference of crab for different mussel sizes

Shore crab Carcinus maenas feeding upon the mussel Mytilus edulis.

Parasitism

• Parasites evolve to reduce damage to host

• Commonly involve complex life cycles with more than one host

• Parasites may invade specific tissues, such as reproductive tissue of the host

Invasion of the parasitic rhizocephalan barnacle Sacculina into the body of a crab

Complex life cycle found in a trematode parasite living in several marine animal hosts

Mutualism: Cleaner wrasse removes ectoparasites from a number of species of fish that visit localized “cleaning stations” on a coral reef. Fish (b) is a mimic species that actually attacks fish that would normally be a “client” of the cleaner wrasse.

Commensalism

Commensal crab and fish live in this burrow of Urechis caupo

Construction of a Population Model

dN/dT = f (N,M,R,I,E)

N = population sizeM = mortalityR = reproductionI = immigrationE = emigration

M is a function of physical environment, competition, predation, etc.

R function of physical environment, resources (e.g., food)

Example of Population Model

Barnacles: What parameters matter the most?

dN/dT = f (N, I, M)

I is larval settlement

M a function of larval-adult interactions, overgrowth, predation

Note R doesn't matter if planktonic larvae mainly go elsewhere

Mortality pattern expected for a species with a planktonic larva. Note higher mortality rate of larval stage.

Planktonic Post-settling stagelarvalstage

Sur

vivo

rs

Modes of Population Change

Exponential Growth

Logistic growth Random change

Metapopulation

• Definition: A group of interconnected subpopulations among which there is movement of individuals

Metapopulation 2

• Definition: A group of interconnected subpopulations among which there is movement of individuals

• Some subpopulations are sources of individuals that move to other subpopulations

Metapopulation 3

• Definition: A group of interconnected subpopulations among which there is movement of individuals

• Some subpopulations are sources of individuals that move to other subpopulations

• Other subpopulations are sinks, which means that they may receive individuals from other subpopulations, but they are not sources (example, only juveniles disperse, but the subpopulation in question does not have individuals that reproduce successfully.

Metapopulation - interconnected group of subpopulations

Spatial Distribution of Individuals

Random Uniform Aggregated

COMPETITION

LIMITING RESOURCES

(1) Renewable - e.g., copepods exploiting diatom population

(2) Non-renewable - space on a rock exploited by long-lived sessile species

Limiting Resources

Space is a limiting resource to these colonies of colonial ascidians

COMPETITIVE DISPLACEMENT - one species outcompetes another for a resource

COEXISTENCE - two species exploit different resources, some process allows two species to exploit same resource withoutdisplacement

Outcomes of Competition

Interference vs. Exploitation Competition

Interference - one species overgrows another, interspecific territoriality, agonistic interaction

Exploitation - one species eats a prey resource more efficiently than another (also called scramble competition)

Styles of Competitive Interaction:

Hierarchy of competitive dominance vs. network

Indirect Effects of Competition

Note: Effectively, B and C beat up on each other, A and B beat up on each other, interaction between A and C is very weak; Bsuffers the most, A and C are not as badly affected.

CONSEQUENCES OF COMPETITION

Extinction: usually local, habitat shift

Coexistence: "niche shift" - character displacement - evolution of shift in morphology or behavior

Variable Environment: Unstable, but can permit coexistence

EVIDENCE FOR INTERSPECIFIC COMPETITION

1. EXPERIMENTAL MANIPULATIONS - remove hypothetical competitor (e.g., barnacles)

2. LABORATORY DEMONSTRATIONS - e.g., growth experiments with one and multispecies combinations - disadvantage is lack of field conditions

3. DISPLACEMENTS IN NATURE - e.g., increase of resource exploitation in estuaries. Problem - other factors could be atwork

4. CONTIGUITY OF RESOURCE USE -e.g., "adjacent niches" - could arise by evolutionary change

EVIDENCE FOR INTERSPECIFIC COMPETITION 2

1. EXPERIMENTAL MANIPULATIONS - remove hypothetical competitor (e.g., barnacles)

2. LABORATORY DEMONSTRATIONS - e.g., growth experiments with one and multispecies combinations - disadvantage is lack of field conditions

3. DISPLACEMENTS IN NATURE - e.g., increase of resource exploitation in estuaries. Problem - other factors could be atwork

4. CONTIGUITY OF RESOURCE USE -e.g., "adjacent niches" - could arise by evolutionary change

EVIDENCE FOR INTERSPECIFIC COMPETITION 3

1. EXPERIMENTAL MANIPULATIONS - remove hypothetical competitor (e.g., barnacles)

2. LABORATORY DEMONSTRATIONS - e.g., growth experiments with one and multispecies combinations - disadvantage is lack of field conditions

3. DISPLACEMENTS IN NATURE - e.g., increase of resource exploitation in estuaries. Problem - other factors could be atwork

4. CONTIGUITY OF RESOURCE USE -e.g., "adjacent niches" - could arise by evolutionary change

EVIDENCE FOR INTERSPECIFIC COMPETITION 4

1. EXPERIMENTAL MANIPULATIONS - remove hypothetical competitor (e.g., barnacles)

2. LABORATORY DEMONSTRATIONS - e.g., growth experiments with one and multispecies combinations - disadvantage is lack of field conditions

3. DISPLACEMENTS IN NATURE - e.g., increase of resource exploitation in estuaries. Problem - other factors could be atwork

4. CONTIGUITY OF RESOURCE USE -e.g., "adjacent niches" - could arise by evolutionary change

RELATION OF PREDATION TO COMPETITION -

Predation suppresses competitive success of superior species over inferior species, especially if predator prefers competitively superior prey

DISTURBANCE

Usually refers to physical change in environment that causes mortality or affects reproduction (storm, ice scour).

SPATIAL SCALE OF DISTURBANCE

Habitat wide (storms, ice, oil spill)

Localized in patches (horeshoe crabs, logs)

EFFECT CAN BE SIMILAR TO PREDATION

Suppresses effect of competition (Intermediate disturbance-predation effect)

Intermediate Disturbance-Predation Hypothesis

Low levels of disturbance or predation: Competitive dominant species takes over

Intermediate levels: Promotes coexistence, more species present

High levels: most individuals removed, reduces total number of species

SUCCESSION

Predictable order of appearance and dominance of species, usually following a disturbance.

SOME MODES OF SUCCESSION

(1) Early species modify habitat, which facilitates colonization by later species

(2) Late species exclude colonization of early species

(3) Early species hold space until death, then are replaced by late species, which do the same

Some Interactions in Succession

Genetic Variation, Species

• Marine species have genetic variation

• Variation found in populations, also frequency of genes varies over space, within a species

• Species are identified by presence of reproductive isolation

Parent-Offspring correlation indicates genetic basis for variation in trait

Cline: A regular change in gene frequencies over a geographic space (here, latitude).

Example: latitudinal change in frequency of the A’ allele in the blenny Anoplarchus purpurescens, in Puget Sound, Washington

Sibling Species in the Sea

Closely related species that are reproductively isolated butvery similar in form, to the point that they cannot be identifiedwithout sophisticated (usually molecular) markers.

Larvae of 5 species of the polychaete sibling species complex Capitella capitata

Evolutionary Tree: established by grouping species with shared characters. Leads to a hierarchy that can be plotted as a tree.

The End