Population Ecology Populations are groups of potentially reproducing individuals in the same place, at the same time, that share a common gene pool. I. Spatial Distributions A. Dispersion

I. Spatial Distributions A. Dispersion - Regular

I. Spatial Distributions A. Dispersion - Regular - intraspecific competition - allelopathy - territoriality

I. Spatial Distributions A. Dispersion - Clumped - patchy resource - social effects

I. Spatial Distributions A. Dispersion - Random - canopy trees, later in succession

I. Spatial Distributions A. Dispersion - Complexities - can change with development. Seedlings are often clumped (around parent or in a gap), but randomness develops as correlations among resources decline. regular can develop if competition becomes limiting.

I. Spatial Distributions A. Dispersion - Complexities - can change with development. Seedlings are often clumped (around parent or in a gap), but randomness develops as correlations among resources decline. regular can develop if competition becomes limiting. - can change with population, depending on resource distribution.

I. Spatial Distributions A. Dispersion - Complexities - can change with development. Seedlings are often clumped (around parent or in a gap), but randomness develops as correlations among resources decline. regular can develop if competition becomes limiting. - can change with population, depending on resource distribution. - varies with scale. As scale increases, the environment will appear more 'patchy' and individuals will look clumped.

Species Interactions Effect on Species 2 Effect on species 1 PositiveNeutralNegative Positivemutualismcommensalconsumer Neutralcommensal-amensal Negativeconsumeramensalcompetition

II. COMPETITION B. Modeling Competition 1. Intraspecific competition

II. COMPETITION B. Modeling Competition 2. Interspecific competition The effect of 10 individuals of species 2 on species 1, in terms of 1, requires a "conversion term" called a competition coefficient (α).

II. COMPETITION A. Modeling Competition B. Empirical Tests of Competition

1. Gauss P. aurelia vs. P. caudatum P. aurelia outcompetes P. caudatum.

B. Empirical Tests of Competition 1. Gauss P. aurelia vs. P. bursaria ):

B. Empirical Tests of Competition 1. Gauss P. aurelia vs. P. bursaria: coexistence ):

B. Empirical Tests of Competition 1. Gauss Why do the outcomes differ? - P. aurelia and P. caudatum feed on suspended bacteria - they feed in the same microhabitat on the same things. P. bursaria feeds on bacteria adhering to the glass of the culture flasks. ):

B. Empirical Tests of Competition 1. Gauss Why do the outcomes differ? - P. aurelia and P. caudatum feed on suspended bacteria - they feed in the same microhabitat on the same things. P. bursaria feeds on bacteria adhering to the glass of the culture flasks. - Gauss concluded that two species using the environment in the same way (same niche) could not coexist. This is the competitive exclusion principle. ):

B. Empirical Tests of Competition 1. Gauss 2. Park Tribolium castaneum Competition between two species of flour beetle: Tribolium castaneum and T. confusum. TEMPHUM T. casteum won (%) T. confusum won (%) COOLdry COOLmoist WARMdry WARMmoist HOTdry HOTmoist

B. Empirical Tests of Competition 1. Gauss 2. Park TEMPHUM T. casteum won (%) T. confusum won (%) COOLdry COOLmoist WARMdry WARMmoist HOTdry HOTmoist Competitive outcomes are dependent on complex environmental conditions Basically, T. confusum wins when it's dry, regardless of temp.

B. Empirical Tests of Competition 1. Gauss 2. Park TEMPHUM T. casteum won (%) T. confusum won (%) COOLdry COOLmoist WARMdry WARMmoist HOTdry HOTmoist Competitive outcomes are dependent on complex environmental conditions But when it's moist, outcome depends on temperature

B. Empirical Tests of Competition 1. Gauss 2. Park 3. Connell ): Intertidal organisms show a zonation pattern... those that can tolerate more desiccation occur higher in the intertidal.

3. Connell - reciprocal transplant experiments ): Fundamental Niches defined by physiological tolerances increasing desiccation stress

3. Connell - reciprocal transplant experiments ): Realized Niches defined by competition Balanus competitively excludes Chthamalus from the "best" habitat, and limits it to more stressful habitat

II. COMPETITION A. Modeling Competition B. Empirical Tests of Competition C. Competitive Outcomes: - Reduction in organism growth and/or pop. size (G, M, R) - Competitive exclusion (N = 0) - Reduce range of resources used = resource partitioning. - If this selective pressure continues, it may result in a morphological change in the competition. This adaptive response to competition is called Character Displacement ):

Character Displacement

III. Predation A. Predators can limit the growth of prey populations

A. Predators can limit the growth of prey populations

Kelp and Urchins In 1940's:

Kelp and Urchins In 1940's:

Moose and Wolves - Isle Royale

1930's - Moose population about 2400 on Isle Royale

Wolves cross on an ice bridge; studied since 1958

1930's - Moose population about 2400 on Isle Royale Wolves cross on an ice bridge; studied since 1958

V. Dynamics of Consumer-Resource Interactions A. Predators can limit the growth of prey populations B. Oscillations are a Common Pattern

IV. Mutualism Trophic Mutualisms – help one another get nutrients

1-Esophagus 2-Stomach 3-Small Intestine 4-Cecum (large intestine) - F 5-Colon (large intestine) 6-Rectum Low efficiency - high throughput...

Trophic Mutualisms – help one another get nutrients

Defensive Mutualisms – Trade protection for food

Acacia and Acacia ants Defensive Mutualisms – Trade protection for food

Cleaning Mutualisms – Trade cleaning for food

Dispersive Mutualisms – Trade dispersal for food Create floral ‘syndromes’ – suites of characteristics that predispose use by one type of disperser

Dispersive Mutualisms – Trade dispersal for food

Not mutualism (commensal or parasitic)

Community Ecology I. Introduction A. Definitions of Community - broad: a group of populations at the same place and time “old-hickory community”

Community Ecology I. Introduction A. Definitions of Community - broad: a group of populations at the same place and time “old-hickory community” - narrow: a “guild” is a group of species that use the same resources in the same way.

Community Ecology I. Introduction A. Definitions of Community - broad: a group of populations at the same place and time “old-hickory community” -narrow: a “guild” is a group of species that use the same resources in the same way. -complex: communities connected by migration or energy flow

I. Introduction A. Definitions B. Key Descriptors Species Richness Species Diversity Evenness Diversity indices Simpson’s: Σ(p i ) 2 Habitat 1Habitat 2 species A species B Richness Simp. Div

C. Conceptual Models 1. Lindeman - 40's - energetic perspective

C. Conceptual Models 1. Lindeman - 40's - energetic perspective - energetic conversion rates determine biomass transfer: - endotherm food chains are short; only 10% efficient

C. Conceptual Models 1. Lindeman - 40's - energetic perspective - energetic conversion rates determine biomass transfer: - endotherm food chains are short; only 10% efficient - ectotherm food chains can be longer, because energy is transfered more efficiently up a food chain (insects - 50% efficient).

C. Conceptual Models 1. Lindeman - 40's - energetic perspective - energy available in lower level will determine the productivity of higher levels... this is called "bottom-up" regulation. not enough energy to support another trophic level

C. Conceptual Models 1. Lindeman - 40's - energetic perspective 2. Hairston, Slobodkin, and Smith (HSS) Observation: "The world is green" - there is a surplus of vegetation

Hairston, Slobodkin, and Smith (HSS) Observation: "The world is green" - there is a surplus of vegetation - Implication: Herbivores are NOT limited by food... they must be limited by something else...predation?

Hairston, Slobodkin, and Smith (HSS) Observation: "The world is green" - there is a surplus of vegetation - Implication: Herbivores are NOT limited by food... they must be limited by something else....predation? - If herbivore populations are kept low by predators, they must be the variable limiting predator populations - as food. SO: Top Pred's: Limited by Competition Herbivores: Limited by Predation Plants: Limited by Competition

Hairston, Slobodkin, and Smith (HSS) Observation: "The world is green" - there is a surplus of vegetation - Implication: Herbivores are NOT limited by food... they must be limited by predation. - If herbivore populations are kept low by predators, they must be the variable limiting predator populations - as food. SO: Top Pred's: Limited by Competition Herbivores: Limited by Predation Plants: Limited by Competition Community structured by "top-down effects" and trophic cascades

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects. Vandermeer 1969 Dynamics in 4-species protist communities of Blepharisma, P caudatum, P.aurelia, and P. bursaria were consistent with predictions from 2- species L-V interactions.

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects so, the addition of a third species changes the effect of one species on another.... which is defined as α 12 N 2.

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects so, the addition of a third species changes the effect of one species on another.... which is defined as α 12 N 2. Well, that means the third species can influence the competitive effect by changing either component ( α 12 ) or (N 2 ).

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects 1. Indirect Effects - mediated through changes in abundance

Worthen and Moore (1991) Indirect, non-additive competitive effects. D. falleni and D. tripunctata each exert negative competitive effects on D. putrida in pairwise contests, but D. putrida does better with BOTH competitors present than with either alone ADDITIVE NON-ADDITIVE

Worthen and Moore (1991) Indirect, non-additive competitive effects. D. falleni and D. tripunctata each exert negative competitive effects on D. putrida in pairwise contests, but D. putrida does better with BOTH competitors present than with either alone D. putrida D. tripunctata D. falleni

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects 1. Indirect Effects - mediated through changes in abundance 2. Higher Order Interactions - mediated through changes in the competitive interaction (coefficient), itself; not abundance consider 2 species, and the effect of N2 on N1 as aN2. N2N1

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects 1. Indirect Effects - mediated through changes in abundance 2. Higher Order Interactions - mediated through changes in the competitive interaction (coefficient), itself; not abundance Now, suppose we add species 3 HERE, as shown... N2N1N3

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects 1. Indirect Effects - mediated through changes in abundance 2. Higher Order Interactions - mediated through changes in the competitive interaction (coefficient), itself; not abundance So NOW, N2 may shift AWAY from N1, reducing its competitive effect. N2N1N3

2. Higher Order Interactions - Wilbur 1972 Ambystoma laterale Ambystoma maculatum Ambystoma tremblay

2. Higher Order Interactions - Wilbur 1972 Mean mass of 32 A. laterale w/ 32 A. tremblayw/ 32 A. maculatumw/both g g g 32 A. laterale alone = g Abundances are constant, so the non-additive effect must be by changing the nature of the interaction

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects 1. Indirect Effects - mediated through changes in abundance 2. Higher Order Interactions - mediated through changes in the competitive interaction (coefficient), itself; not abundance 3. Mechanisms: Change size of organisms and affect their competitive pressure Change activity level and affect their resource use Change behavior... and resource use

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects C. Results

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level A. Additive Competitive Effects B. Non-Additive Competitive Effects C. Results 1. Niche Partitioning at the Community Level: Species Packing There should be a non-random ordering of species along some resource axis or associated morphological axis This can be tested through nearest neighbor analyses. What would you see if they were ordered randomly? Then compare.

1. Niche Partitioning at the Community Level: Species Packing Dayan et al., Species packing in weasels in Israel.

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level III. Multispecies Interactions across Trophic Levels

Community Ecology I. Introduction II. Multispecies Interactions with a Trophic Level III. Multispecies Interactions across Trophic Levels A. Keystone Predators

1. Paine (1966) - the rocky intertidal Arrows show energy flow; point to consumer.

A. Keystone Predators 1. Paine (1966) - the rocky intertidal - Pisaster prefers mussels

A. Keystone Predators 1. Paine (1966) - the rocky intertidal - Pisaster prefers mussels - When predators are excluded, mussels outcompete other species and the diversity of the system crashes to a single species - a mussel bed

A. Keystone Predators 1. Paine (1966) - the rocky intertidal - Pisaster prefers mussels - When predators are excluded, mussels outcompete other species and the diversity of the system crashed to a single species - a mussel bed - When predators are present, the abundance of mussels is reduced, space is opened up, and other species can colonize and persist.

A. Keystone Predators 1. Paine (1966) - the rocky intertidal - Pisaster prefers mussels - When predators are excluded, mussels outcompete other species and the diversity of the system crashed to a single species - a mussel bed - When predator is present, the abundance of mussels is reduced, space is opened up, and other species can colonize and persist. So, although Pisaster does eat the other species (negative effect) it exerts a bigger indirect positive effect by removing the dominant competitor