1. The Ecological Niche and Ecological Niche Modeling
Tereza Jezkova
School of Life Sciences, University of Nevada, Las Vegas
Modified, T Kittel
March 2012

2. What drives species distributions?
All species have tolerance limits for environmental factors beyond which individuals cannot survive, grow, or reproduce

3. Tolerance Limits and Optimum Range Tolerance Limits
Environmental Gradient
Tolerance limits exist for all important environmental factors

4. Critical factors and Tolerance Limits

5. Critical factors and Tolerance Limits
For some species, one factor may be most important in regulating a species’ distribution and abundance.
Usually, many factors interact to limit species distribution.

6. Critical factors and Tolerance Limits
Organism may have a wide range of tolerance to some factors and a narrow range to other factors

7. FUNDAMENTAL NICHE Biotic factors Historical factors REALIZED NICHE
Historical - might do well somewhere but not there because of dispersal
Biotic - predation etc
Realized envir- what actually available
Realized niche = Actual niche
Realized
environment

8. Fundamental versus realized niche
Tolerance Limits and Optimum Range
Fundamental versus realized niche
Fundamental (theoretical) niche
- is the full spectrum of environmental factors that can be potentially utilized by an organism
Realized (actual) niche
- represent a subset of a fundamental niche that the organism can actually utilize restricted by:
- historical factors (dispersal limitations)
- biotic factors (competitors, predators)
- realized environment (existent conditions)

9. Tolerance Limits and Optimum Range Niche shift
Are niches stable?
Realized niche shifts all the time due to
changing biotic interactions,
realized environment,
time to disperse
NO!
Time T1
Time T2
Realized
Niche
Shift
all niche categories can change with time
eg last glacial max (LGM) = environ changes
Fundamental niche can also change - but this requires evolutionary shifts - can't predict. Can be adaptive (deterministic) or non-adaptive (e.g., bottlenecks; random: genetic drift)

10. Fundamental niche shift when tolerance limits change  due to EVOLUTIONARY ADAPTATION
Time T1
Time T2
Fundamental
Niche
Shift

11. Resource Partitioning
Law of Competitive Exclusion - No two species will occupy the same niche and compete for exactly the same resources
- Extinction of one of them
- Niche Partitioning (spatial, temporal)

12. Niche partitioning and Law of Competitive Exclusion
Chthamalus
Balanus
Chthamalus
Balanus
famous example of niche partitioning - experimental removal of 1 or other sp

13. Niche partitioning and Law of Competitive Exclusion
2 spp of Anolis - ~same size, same food types (smaller liz's)
some islands -one goes extinct
other islands - one eats small food
another - one feeds in trees, other on ground

14. Ecological niche modeling
Purpose: ·   
- Approximation of a Species Distribution
    
use of Species Niche Modeling -
to get better idea of species distribution - in case of incomplete field sampling
--> where are ideal for a species, where might go look for the species

15. Ecological niche modeling
Purpose: ·  
     - Potential Niche Habitat Modeling
(Invasive species, diseases)
   

16. Ecological niche modeling
Purpose: ·   
    - Site Selection or conservation priority:
Suitability Analysis
blue area - ideal for species

17. Ecological niche modeling
Purpose: ·      
- Species Diversity Analysis
Overlap many models to get spp diversity

18. Ecological niche modeling
Two types:
1. DEDUCTIVE: A priori knowledge about the organism
Example: SWReGAP
projecting habitat distribution in GIS

19. Ecological niche modeling
Two types:
2. CORRELATIVE: Self-learning algorithms based on known occurrence records and a set of environmental variables

20. Occurrence records:
Own surveys (small scale)
Digital Databases (e.g. museum specimens)
MANIS (mammals)
ORNIS (birds)
HERPNET (reptiles)
HAVE TO BE GEOREFERENCED (must have coordinates)

21. WORLDCLIM http://worldclim.org/
Variables:
Temperature (monthly)
Precipitation (monthly)
19 Bioclimatic variables
Current, Future, Past
Resolution:
ca. 1, 5, 10 km
Coverage
World

22. Southwest Regional Gap Analysis Project http://earth.gis.usu.edu/swgap
Northwest GAP Analysis Project
Variables:
Landcover
Resolution:
ca. 30 m
Coverage
western states

23. Natural Resources Conservation Service (NRCS)
SSURGO Soil Data
Variables:
Soils
Resolution:
ca. 30 m
Coverage
USA but incomplete 

24. Ecological niche modeling
Step 1: occurrence records
Step 2: environmental variables
Step 3: current ecological niche
Step 4: projected ecological niche
4th diagram: predict species distribution in time, e.g. past or future environmental conditions. --
How are these predictions made?
In general, they use the methodology of ecological niche modeling. This methodology can be described in four steps.
First, the researchers assemble occurrence records for the target species – coordinates where the species was documented as “present. Second, they assemble digital maps environmental variables that they suspect could be important in delimiting the species distribution – these environmental variable could be climate (tem and prec), also soils, vegetation, food resources, competition and so on. This simple example would represent temperature along elevation gradient or latitudinal gradient.
In the third step, they delimitate suitable habitat based on the information learned from the occurrence records – the green rectangle represent the suitable niche for our hypothetical species.
In the fourth step, the same environmental variables are obtained under a scenario of a climate change, in this case global warming, and the range shift is inferred. But this methodology makes one major assumption: What is it?______

25. Ecological niche modeling – models from Maxent

26. !!! WRONG INTERPRETATIONS !!!
Problems: Models are only as good as the data that goes into it!!!
Calibration of Models
Insufficient or biased occurrence records
Insufficient or meaningless environmental variables
Projection-Source Model
Inaccuracies in climate reconstructions
Dispersal limitations
Non-analogous climates
Niche shift (evolution)
Problems
models not perfect -- lot of things that can bias model results
using the wrong / irrevant variable - e.g. winter air T vs. in burrows.
no analog climate today in past/future
!!! WRONG INTERPRETATIONS !!!

27. sasquatch
blackbear