Niche Theory

Question 1

Niche 1

Answer 1

Grinnell 1917

• descriptive study of California thrasher species distribution in California
• followed climate
• emphasised conditions
• made point no two species have identical niche relationships

Question 2

Advancements made from niche 1

Answer 2

• plot two variables of a species habitat and overlay species quantity = graph of climate niche
• Outer points can be linked to give boundaries for the variables

Question 3

Niche 2

Answer 3

Elton 1927

• functional role of species and its interactions with other species in community
• emphasised resources
• more difficult to quantity the interactions
• modern tech helps e.g. molecular analysis of faeces

Question 4

Advancements made from niche 2

Answer 4

Suggests you can determine species trophic niche by the size of their prey

Question 5

Niche 3

Answer 5

Hutchinson 1957

• considered both conditions and resources
• n-dimensional hyper volume: consists of all variables that allow species to survive and multiply
• organism cannot exist outside of hyper volume
• uses fundamental and realised niches
• impossible without software, plots mathematically

Question 6

Advancements made from niche 3

Answer 6

Graph created to show the effect of two conditions on species fitness

• point size = performance
• can overlay multiple species…suggest if species can coexist in same habitat
• better competitor will win and can be determined by overlayed boundaries: overlay is close to other species centroid (largest fitness point) then competitor probably wont exist there.

Question 7

Possible responses to climate change

Answer 7

• track the climate niche through space e.g. move to higher altitudes
• adapt; phenotypic plasticity, evolution
• extinction

Question 8

R threshold

Answer 8

The point on a graph where the spices changes from present to not present
R = 0

Question 9

Thomas et al (2004) species distribution model

Answer 9

Extinction risk by 2050
1100 plant and animal species 
5 continents 
3 emission scenarios 
Predicted extinction rate of 9-32% 
Quite a simple study but helped get idea of future

Question 10

Tingley et al (2009) species distribution model

Answer 10

Recreated Grinells bird survey
Breeding season warmer (by 0.8C) and wetter (by 6.9mm)
Birds particularly good at tracking climate shifts: 91% birds tracked temp or precipitation

Question 11

Problems with species distribution models

Answer 11

1. Which niche is modelled?
   - grinnellian, fundamental vs realised
2. Niche may need to change
   - can happen in short time scale

But next-gen SDM starting to include species interaction dispersal mechanisms = more realistic to realised niche

Question 12

E.g. of niche changing over time

Answer 12

Crozier et al 2011
Over 6 years
Sock eye salmon migration up Colombia river
Summer water temp increased by 2.6C = migrations starts 10 days earlier
- around 50% of change is evolutionary response to warmer temps = selection pressure

Question 13

E.g. of direct evidence of niche shifts

Answer 13

• if niche changes species will follow original climate
  Broenimann 2007
• Spotted knapweed native to E. Europe
• introduced to America = now invasive
• change in location caused large change in niche: preferred wet and now prefers dry

Question 14

Potential causes of niche shifts

Answer 14

1. Change in fundamental niche
   - idea of niche conservatism
   - evolutionary processes may invalidate this
2. Changes in realised niche
   - e.g. competitors, predators etc
   E.g. spotted knapweed escaped soil pathogens and specialists herbivores found in native range

Question 15

Grinnellian niche

Answer 15

• niche determined by habitat
• species will meet the abiotic habitat requirement and behaviours needed to persist and reproduce
• best applied to broad scales

Question 16

Eltonian niche

Answer 16

• emphasises the functional attributed of animals and their trophic position
  -less popular now than grinnellian
  More about how a species affects its habitat
• best at local scales