Population Ecology I. Attributes II.Distribution

Population Ecology I. AttributesII.DistributionIII. Population Growth – changes in size through timeIV. Species InteractionsV. Dynamics of Consumer-Resource InteractionsVI. CompetitionVII. Mutualisms

A. Overview1. Dynamics- NET fitness benefit to both populations- diffuse (many partners) or species specific- facultative (not necessary) or obligate- strength of feedback loop depends on the degree of “obligateness”

A. Overview1. Dynamics2. Historical Importance - endosymbiotic origin of Eukaryotes

A. Overview1. Dynamics2. Historical Importance - endosymbiotic origin of Eukaryotes - symbiotic origin of multicellularity

A. Overview1. Dynamics2. Historical Importance - endosymbiotic origin of Eukaryotes - symbiotic origin of multicellularity - symbiotic efficiencies in energy harvest by nearly all life forms

Corals and zooxanthellae

Gleaners

Aphid farming by antsFrugivory

PollinationProtozoans in Termites

A. Overview1. Dynamics2. Historical Importance - endosymbiotic origin of Eukaryotes - symbiotic origin of multicellularity - symbiotic efficiencies in energy harvest by nearly all life forms - at planetary scale, there are complementary and dependent roles

White – increase reflectance, lower temperature of planet. White flower doesn’t overheat, but doesn’t work well at low temps.

Black – increase absorption, increase temperature of planet. Work well at low temps, but overheat at high temps.

dN1/dt = rN1 ((K1-N1 + aN2)/K1)

dN2/dt = rN2 ((K2-N2 + bN1)/K2)

A. OverviewB. Modeling Mutualism

Effect of second species increases population growth

N2 reaches its K when N1 = 0. But N2 > K when N1 > 0.

N1 increases (beneath its K), but N2 declines because there aren’t enough N1’s to allow N2 to maintain this large a population.

Both get bigger and bigger (run-away)

Stable equilibrium – both maintained at a stable equilibrium above K.

Obligate mutualism – a minimum number of partners are required to maintain a population above zero. So, there needs to be at least 50 N2 individuals for N1 to grow (above its isocline). To sustain more N1 individuals, more N2 are needed.

So here, there are 170 N2 individuals and that’s enough for the 5 individualsIn the N1 population to grow. However, with only 5 N1 individuals, N2 declines. This eventually causes a decline in N1, as they are obligate mutualists.

C. Types of MutualismTrophic 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...








Rhizobium bacteria fix nitrogen, breaking N2 into N, which reacts with water and oxygen to form NO2 and NO3 that can be absorbed by plant. Infect legumes; plant provides sugars.


Ectomycorrhiza and “Endo”- or arbuscular mycorrhizae

Trophic Mutualisms – help one another get nutrientss

Lichens – an alga and a fungus

Trophic Mutualisms – help one another get nutrients

Mixed foraging flocks

Defensive Mutualisms – Trade protection for food


Ants ‘farm’ the fungus, culturing it on a chewed-leaf mulch.

Acacia and Acacia ants


Induced and Constitutive Defenses in Acacia.

The species in the right-hand column have mutualistic relationships with ant species - the ants nest in the thorns. Those on the left can attract ants with extra-floral nectary secretions, but the ants do not nest.

The Acacia species on the left increase their nectar secretions after damage, inducing wandering ants to come visit and stay a while.

The species on the right have to support the ant colonies all the time, and nectar production is uniformly high and unaffected by damage.


The species in the right-hand column have mutualistic relationships with ant species - the ants nest in the thorns. Those on the left can attract ants with extra-floral nectary secretions, but the ants do not nest.

The Acacia species on the left increase their nectar secretions after damage, inducing wandering ants to come visit and stay a while.

The species on the right have to support the ant colonies all the time, and nectar production is uniformly high and unaffected by damage.

WHICH CAME FIRST??


Induced defenses first, then the obligate relationship evolved…

Fig. 1. Rewards produced in the presence (white bars) and absence (gray bars) of large herbivores by A. drepanolobium occupied by different species of Acacia ants. Ant species' abbreviations are indicated as: Cs, C. sjostedti; Cm, C. mimosae; Cn, C. nigriceps; Tp, T. penzigi.

Todd M. Palmer, Maureen L. Stanton, Truman P. Young, Jacob R. Goheen, Robert M. Pringle, Richard Karban. 2008. Breakdown of an Ant-Plant Mutualism Follows the Loss of Large Herbivores from an African Savanna. Science 319:192-195.

Plants produce fewer rewards when large herbivores are absent and herbivory rates are LOWER. Bribing ants to stay and protect them is less important.


Fig. 2. The proportion of host trees occupied by the four Acacia-ant species in the presence of large herbivores (white bars) and in plots from which large herbivores had been excluded (gray bars) for 10 years.

And if large herbivores are excluded and plants produce less nectar, then some ants abandon the trees (the mutualist).

“Our results indicate that the large herbivores typical of African savannas have driven the evolution and maintenance of a widespread ant-Acacia mutualism and that their experimentally simulated extinction rapidly tips the scales away from mutualism and toward a suite of antagonistic behaviors by the interacting species. Browsing by large herbivores induces greater production of nectary and domatia rewards by trees, and these rewards in turn influence both the behavior of a specialized, mutualistic ant symbiont

and the outcome of competition between this mutualist and a non-obligate host-plant parasite. Where herbivores are present, the carbohydrate subsidy provided by host trees plays a key role in the dominance of the strongly mutualistic C. mimosae, which is consistent with the hypothesis that plant exudates fuel dominance of canopy ant species that are specialized users of these abundant resources (28). In the absence of large herbivores, reduction in host-tree rewards to ant associates results in a breakdown in this mutualism, which has strong negative consequences for Acacia growth and survival. Ongoing anthropogenic loss of large herbivores throughout Africa (29, 30) may therefore have strong and unanticipated consequences for the broader communities in which these herbivores occur.”



Ants ‘farm’ aphids and drink their ‘honeydew’

Cleaning Mutualisms – Trade cleaning for food



And watched cleaners cheat less.

Fish visit non-cheating cleaners more

Dispersive Mutualisms – Trade dispersal for food



Orchids, Euglossine Bees, and Wasps.



Not mutualism (commensal or parasitic)

Mutualisms in Mimicry:

“Mullerian” mimicry – toxic species resemble one another

Gain an advantage by converging on a common phenotype; prdators eat one and learn to avoid both.

Population Ecology I. Attributes II.Distribution

Documents

n1 population

n1 individuals

n2 individuals

n2 declines

symbiotic efficiencies

population growthn2

population ecologyi

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