Ecology Exam 3 Sp26

Leaf Cutter Ants (chp 15)

Leaf-cutter ants (Atta cephalotes) Costa Rica carry leaf segments to their colony, where

the leaves will be fed to the fungus (the gray material) the ants cultivate for food.

Positive interactions

One or both species benfit and neiter is harmed (Example Mycorrhizae

Symbiosis

Two species in close physical contact with each other

Symbiosis → Parasitism

(+ / -) interaction

Symbiosis → Commensalism

(+ / 0) relatioship
Individuals of one species benefit; individuals of the other species do not benefit byt are not harmed

Symbiosis → Mutualism

(+ / +) relatioship
Mutually beneficial interaction between individuals of two species

Cost vs Benefits of Mutualisms

Benefits take many forms—food, shelter,

transport, etc.

cost to one or both partners, but the net

effect is positive.

For each species, the benefits are greater

than the costs.

Ectomycorrhizae

A type of Mutualism fungus that forms a sheath around the roots of certain trees (like pines and oaks), helping the plant absorb water and nutrients (especially phosphorus and nitrogen) while receiving sugars in return. It stays mostly outside root cells, forming a network between root cells called the Hartig net.

Arbuscular mycorrhizae (VAM)

A type of symbiotic fungus ( Mutualism) that penetrates the root cells of most herbaceous plants, forming tree-like structures called arbuscules inside the cells. These structures help the plant absorb nutrients (especially phosphorus) and water more efficiently, while the fungus receives sugars from the plant.

Corals and algae

Tiny algae called zooxanthellae live inside coral tissues. The algae perform photosynthesis, providing the coral with sugars for energy, while the coral offers the algae a protected home and access to sunlight. Both benefit, making this a mutualistic relationship.

Ruminants

Ruminants are animals (like cattle and sheep) that have a multi-chambered stomach (rumen, reticulum, omasum, abomasum) to digest cellulose from plant material. Microbes in the rumen ferment plant fibers, producing volatile fatty acids for energy, while the microbes get a steady food supply.
mutualistic relationship.

Wood Eating insects (cockroach)

wood-eating cockroach (and other wood-eating insects, e.g. termites) would starve if gut mutualists such as the protist (hypermastigote) did not help it to digest wood (cellulose)

mutualistic relationship.

Lichens on Trees

Commensalism

Bacteria on human skin

Commensalism

Obligate/ coevolution

• Obligate means necessary – both species depend entirely on each other to survive and reproduce.

• Coevolution means the species have evolved together, influencing each other’s traits over time.

Example:

• Fig trees produce flowers that can only be pollinated by specific fig wasps.

• Fig wasps can only reproduce by laying eggs inside fig flowers.

• The wasp pollinates the fig while laying its eggs, so both species’ survival is linked.

Facultative commensalisms are not Coevolution

In deserts, the shade of adult plants creates cooler, moister conditions. Seeds of many plants can only germinate in this shade. The adult is called a nurse plant. But seeds can germinate under various pecies of nurse plants.

Relative Neighbor Effect

A concept in ecology that measures how neighboring plants influence the growth or survival of a focal plant.

• If neighbors help the focal plant (e.g., by providing shade or nutrients), the RNE is positive.

• If neighbors harm the focal plant (e.g., through competition for light, water, or nutrients), the RNE is negative.

Trophic mutualisms (examples)

Mutualist receives energy or nutrients from its partner.

• Mycorrhizae

• Coral-alga symbiosis

• Leafcutter ant + fungus

Habitat mutualisms (example)

One partner provides the other with shelter, living space, or favorable habitat

• Shrimp and Goby

How do Medicago truncatula plants “reward” mycorrhizal fungi in terms of phosphorus supply?

Plants selectively allocate more carbohydrates to fungi that provide higher phosphorus, rewarding helpful partners, rather than giving sugars equally to all fungi. (Selective mutualism vs. promiscuous)

Selective Mutualism

A type of mutualism where a species rewards partners that provide the most benefit, giving more resources or attention to the most helpful partner.

Promiscuous Mutualism

A type of mutualism where a species gives benefits equally to all partners, regardless of how much each partner contributes.

Yuccas and Yucca Moths

This is a classic example of obligate mutualism:

• Yucca plants rely on yucca moths for pollination. Without the moth, the plant cannot reproduce.

• Yucca moths rely on yucca flowers to lay their eggs. Their larvae feed on some of the developing seeds.

• The moth actively pollinates the flower while laying eggs, ensuring both species benefit.

• Cheaters lose: If the plant detects poor pollination or too many eggs, it may abandon or abort the flower, killing the moth’s larvae.

Janzen (1966)

studied Acacia trees and their ant defenders. He found that ants protect the tree from herbivores in exchange for food (nectar) and shelter (hollow thorns). Trees with ants grow bigger, survive better, and are less damaged by insects.

Communities (chp 16)

groups of interacting species that occur together at the same place and time

Caulerpa taxifolia (Killer alga)

• It was unintentionally released into the Mediterranean by the Oceanographic Museum of Monaco.

• Its invasive range extends at least as far as Spain on the west and Croatia on the east.

• has evolved cold resistance.

What is the primary difference between interaction webs and food webs?

Interaction webs include non-trophic interactions, where food webs do not.

omnivores

Species that feed on more than one trophic level are called

The Shannon index is a measure of

species diversity.

Which statement describes a limitation of a species accumulation curve in terms of its ability to determine whether species diversity has been adequately sampled?

It assumes that the sampling methods are consistent throughout the study.

functional group.

All the plant species in a community that have nitrogen-fixing bacteria (e.g., legumes) could be placed in the same functional group

Guild

All the species that use pollen as a resource could be grouped together as a guild

Trophic levels Autotrophs

primary producers

Trophic levels Herbivores

Primary consumers

Trophic levels carnivores

Secondary consumers

Trophic levels- carnivores²

Tertiary consumers

Species Richness

species number

Species Evenness

relative abundances

In Shannon index pi

proportion of individuals in the ith species (relative abundance)

In shannon idex equation “s”

Number of species in the community

Biodiversity

describes diversity at multiple spatial scales, from genes to species to communities.

• Genetic diversity affects population viability

• Which affects species diversity in a community

• Which influences the diversity of communities at larger scales

Hughes and colleagues

found that communities of five different types varied greatly in the sampling effort that would be needed to estimate their species richness.

Trophic cascade

trophic cascade occurs when a carnivore feeds on an herbivore and thus has an indirect positive effect on a primary producer that is eaten by that herbivore.

• Sea otters feed on urchins saving kelp

Trophic facilitation

Trophic facilitation occurs when a consumer is indirectly helped by a positive interaction between its prey and another species

• The interaction between Juncus and Iva has an indirect positive effect on the aphids that feed on Iva

Juncus and Iva relatioship

• Juncus shades the soil surface, decreasing evaporation and salt buildup.

• Juncus also has aerenchyma, a tissue that allows oxygen to move to the roots. Some oxygen moves into the soil where other plants can use it.

Competitive network

Circular network, indirect species interactions buffer strond direct competition so no one species dominates the interaction

Competitive hierarchy

A linear hierarchical view speceies A always dominates the interaction

Keystone species

have large effects on their communities despite their small size and abundance

Foundation speceis

Have large effects on their communities by virtue of their large size and abundance

Interaction strength

Magnitude of the effect of one species on the abundance of another

• Measured by removing one species from the community and observig the effect on the other species

Per capita interaction strength = (Ln(C/E))/I

• C= Number of target individuals with interactor present

• E= Number of target individuals with interactor absent

• I= Number of interactor individuals

Menge et al 1996

Measured interaction strength of sea star (pisaster) predation of mussels (Mythilus) in wave-exposed versus wave protected areas

• Interaction strenght was greater in protected areas

What species can be both Foundation and Ecosystem engineering species

Trees

• Tress leaves branches and trunk provide habitat for other species

• Tress affect temp and moisture

• Fallen trees can serve as nurse logs

• Trees leaves fall to the forest floor providint more habitat

• Tree roots aerate soil, and stabilizing forest floor

Beavers are…

Keystone species and Ecosystem engineers

• Increase wetland area by building dams

Which statement about keystone predators is true?

 

They usually influence primary producers indirectly.

The lowest possible value of the Shannon index is _______. Low values indicate _______ species diversity.

0 and low

A linear species accumulation curve

Means more sampling is nessary

Hacker and colleagues (Juncus and Iva)

trophic facilitation phenomenon: the Juncus and Iva have

• Commensalism Juncus help Iva

• Aphids then eat Iva

Power and colleagues of northern California rivers

showed that the strengths of species interactions can vary depending on the environmental context

Estimates show that oceans absorb about what percentage of atmospheric CO₂?

48%

The invasion of the seaweed Caulerpa into Mediterranean coastal communities has had which major effect on these communities?

It has damaged these communities by causing a decline in the foundation seagrass species Posidonia

Succession

A regular pattern of change through time in the composition and structure of a community following a disturbance.

Primary succession

starts at a new substrate where no plants have been before and proceeds to a new community. This is usually from bare rock to lichens to soil to trees in most texts.

Secondary succession

starts at a disturbed substrate where there has been life before and proceeds to climax. Usual examples are old field to forest succession or bog to coniferous forest succession.

Climax

Theoretical “steady state” wherein composition and structure do not change.

Disturbance

Events that injure or kill some individuals and create opportunities for other individuals (like a tsunami)

Stress (agents of change)

Abiotic factors that reduce growth, reproduction, or survival of individuals

GPP

Gross primary Production

NPP

GPP (minus) - energy used by plants

NEP

NPP- Energy used by all life

Pioneer/Early Successional ( Primary succession)

Usually small, stress tolerant organisms (lichens weeds)

Intermediate (seconday succession)

Usually grasses to shrubs and trees

Climax (seral stages of succession)

Usually thought to be trees, long lived and can reproduce in their own shade and under normal disturbance conditions

Chronosequence

A study of succession in which variation in composition and structure is due to time since disturbance. Disturbances assumed to be the same

• H. C. Cowles, Indiana. Dunes (1898): assuming communities closest to the lake were primary and as they get farther from the disturbance the successional stages increased,

Frederic Clements said

plant communities are “superorganisms,” groups of species working together toward some deterministic “climax” community

Henry Gleason

thought that communities are the random product of fluctuating environmental conditions acting on individual species

Charles Elton

was influenced by these botanists (Gleason and Clemens) and by his interest in animals. worked with English Pine Forests.

• Wetlands → sphagnum bogs

• Drier areas. → Grass and sedge marshes

Facilitation model

Early species modify the environment in ways that benefit later

species. But- inhibit early species. The sequence of species facilitations leads to a climax community.

Inhibition model

early species modify conditions in negative ways that hinder later successional species.

Tolerance Model

early species modify the environment in neutral ways that neither benefit nor inhibit later species but inhibit early species

Glacier Bay has elements of all three models proposed by Connell and Slatyer (1977)

• Facilitaion (early stage plants)

• Tolerance (Spruce Climax)

• Inhabition (alders, intermidaites)

Bertness and Shumway (1993)

They studied how the plant Spartina alterniflora affects other plants. In harsh, stressful conditions (like high salinity and flooding), Spartina actually helps neighboring plants survive by reducing stress (facilitation). But in less stressful conditions, it competes with them for resources like light and nutrients.

• found that Distichlis facilitated colonixation by juncus

Mechanisms of Succession

• Crabs like Ulva (early stage) removing primary successor

• Mid-successional species more susceptible to stress and epitytes

• Gigartina dominated becasy least susceptible to stress and herbivores (Climax)

Chthamalus dalli (Farrell 1991) experiment

supporting the facilitation model

• Macroalgae reached the highest densities in plots where balanus was present and limpets were absent

Lewontin (1969): alternative stable states

A community is thought to be stable when it returns to its original state after perturbation.

Alternative Stable States

there are multiple valleys that a community can rest in and be stable

• a change can push the community to move to a differnt state (valley)

• reversal of change does not alwasy result in orginal conditioins

MOUNT St HELEN is an example of this

Dwarf lupine (Lupinus lepidus),

A legume with symbiotic nitrogen-fixing bacteria was the first plant to colonize Mount St. Helens.

Kauris (North Island of New Zeland)

One of the largest trees species on eath

Biological Dynamics of Forest Fragments Project (BDFFP)

• Manaus Brazil

• to study the effects of habitat fragment size on species diversity

Spatial scales of species Diversity

1. Global Scale ( on earth)

2. Regional scale ( y= gamma), drived by dispersal

3. Landscape scale ( b= beta/turnover),

4. Local scale (a= alpha), driven by physical condition and species interactiosn

Species Richness curve

• When Local and regional species richness are equal (slope=1). All species will be found in the communities of that region

• When local richness values are lower then regional richness values (slope<1, still straight)

• Local richness stays the same as regional richness increases (a curce levels off)

Witman et al (2004)

showed that in 49 sampling sites had a slope of 0.75

• this shows that regional species pools largerly determine local species richness

Alfred Russel Wallace

Father of Biogeography

• Also natural selection

Wallace and Weber Lines

• Wallaces Line (1859

• Webers Line (1900

Vicariance

Separation of species by barriers such as those formed by continental drift

Wallaces Biogeographic regions

They roughly correspond to earths major tectonic plates

• Nearctic= North american

• Neotropical= South american

• Ethiopian= African

• Palearctic= Eurasian plate

• Oriental

• Australasian

Subduction Zone

One plate is forced under another

Pangaea Breakup

251 MYBP

Diversification rate

The tropics have high diversitcation rate; due to stable environment and large land area= low extinction

• Michael Rosenzweig