Lecture 10 Interactions And The Niche

Question 1

Ecology

Answer 1

Scientific study of the distribution of abundance of organisms and the interactions that determine their distribution and abundance

Question 2

3 key factors

Answer 2

Where - distribution
How many - abundance/ diversity
Why there? Interactions

Question 3

Ecology includes

Answer 3

Individual organisms
Populations ( 1 species)
Communities (>1 species)
Ecosystems
Biomes

Question 4

Ecology doesn’t include

Answer 4

Biological hierarchy - taxonomy
Subcellular particles, cells, tissues and organs - physiology

Question 5

Interactions

Answer 5

Classified according to impact of interaction on specie involved : positive, negative or no effect

Classified according to trophic (feeding) or non trophic

Question 6

Predation (trophic)

Answer 6

Predator consumes individual/ parts of individual of another species (prey) - may or may not involve killing

Prey, carnivory, herbivory, parasitism

Question 7

Non-trophic: Interspecific competition

Answer 7

Two or more species overlap in use of one or more of the same limited resources leading to reduced growth, reproduction or survival (ie lower fitness) such as competition for food or nesting space or light in plants

Question 8

Trophic/non-trophic: interspecific facilitation

Answer 8

At least one species benefits from interacting, neither is harmed. Mycorrhizal networks in plants , plant pollinator interactions are mutualistic/ mutualisms - both parties benefit. Commensalism one partner benefits and other is unaffected e.g. shrubs and grasses able to grow under “nurse trees” on savannah protected from harsh sun

Question 9

Amensalism

Answer 9

One species neg affected by other whilst the other is unaffected by the interaction e.g. seedlings on forest floor unable to grow due to larger plants blocking sunlight - larger plants unaffected. Destruction of plants by elephant as it walks - does not effect elephant.

Question 10

Symbiosis

Answer 10

One specie lives in/on another - close and long-term biological interaction. May be mutualistic or parasitic.

Mutualistic e.g.mycorrhizal fungi in plant roots plant recieves nutrients and fungi recieves carbohydrates (particularly underpins survival of orchids.)

Parasitic - host symbiosis - many parasites specific to host e.g. human head louse and cannot survive independently from partner (obligate) human head louse has an endosymbiotic bacteria in them vital for B5 synthesis (mutualistic symbiosis)

Example:
African buffalo feeds on savannah grass - herbivory
Oxpeckers eat parasitic ticks off the buffalos back
- parasitism, predation, mutualism
Ox destroys insect nests as it walks. White cattle egret feed on insects disturbed by the buffalos passage
- amensalism and commenalism

Question 11

Interactions

Answer 11

not binary
often not symmetrical
strength of interaction vary
may be stronger in one direction than another
eg. In UK grey squirrels expert stronger competitive effect on red squirrels.

Question 12

Interactions shift

Answer 12

Can shift between neg and pos due to enviro conditions e.g. shrubs and trees have amensal or commensal interactions depending on intensity of the sunlight - shade can protect (commenalism) or block photosynthesis (amensalism)

Question 13

Commensalism

Answer 13

One species positively affected whilst other is unaffected or unharmed e.g. white cattle egret feed on insects disturbed by buffalo walking - egret benefits, buffalo unaffected

Question 14

Effects of interactions

Answer 14

Population dynamics
Competitive exclusion
Ecosystem function/properties
Community composition
Species distribution
Evolution

Question 15

Predation and population dynamics

Answer 15

Regulate oneanother - other factors can produce cycling effects too

Question 16

Competitive exclusion

Answer 16

Can prevent coexistence of species w/strong overlap in resource requirements

Question 17

Competition, predation and community composition

Answer 17

Interactions can remove dominant species allowing others to persist e.g. starfish preying on mussels reduce their dominance in intertidal communities allowing more species to establish themselves

Question 18

Interactions and community dynamics

Answer 18

Can drive process of succession over time- changes in communities e.g. due to receding ice caps

Question 19

Interactions and ecosystems

Answer 19

Reintroduction of wolves into Yellowstone NP caused tritrophic cascade- reduced elk pop. Allowing aspen to recruit and regenerate particularly in riparian zones - wolf acts as keystone species

Question 20

Evolution

Answer 20

Competition may lead to evolution of differentiated resource use resulting in avoidance of competition and speciat89!.
10 herbs in ginger family live in Costa Rican rainforest all are pollinated by hermit hummingbird they coexist by flowering at different times (different flower phenology) avoiding competition

Question 21

Niches

Answer 21

In ginger plant - hummingbird example past competition is thought to have resulted in evolution of differentiated niches
In general a species niche can be considered as the role and position a species has in its environment including abiotic and biotic factors. so niches are a product of interactions

Question 22

How to visually represent niches

Answer 22

1 dimensional: repro success Vs survival fitness (hyperbola)

2 dimensions e.g. precipitation Vs temp

3 dimensions soil pH Vs precipitation and temp

Width of dimension where species maintain fitness can be thought of as “niche breadths”

Narrow niche = specialism
Broad niche = generalist

Fundamental niche = range of abiotic enviro conditions that species (individual/population) can persist in

Realised niche= portion of fundamental niche that can be occupied accounting for biotic factors - almost always smaller and never larger than fundamental niche

Question 23

Interactions summary

Answer 23

Interactions can be classified according to effect on organisms involved and whether or not they are trophic

Can vary in strength/direction depending on enviro conditions and partners involved

Far reaching effects: pop. Dist. Communities, ecosystems and evolution

Help define a species niche (forming realised niche from fundamental)