Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A...
Transcript of Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A...
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Stable isotopes as descriptors of ecological niches
Loïc MICHEL – [email protected] "Etude des isotopes stables et applications au milieu marin" – 12/2018
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What’s an ecological niche?Joseph Grinnell (1917): "habitat niche"
The niche of a species is the sum of the habitat requirements and behaviors that allow it to persist and produce offspring
The Auk 34: 427–433
Chaparral
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What’s an ecological niche?Charles S. Elton (1927): "functional niche"
"The "niche" of an animal means its place in the biotic environment, its relations to foodand enemies."
Species respond to their environment and affect it: their niche is the role they perform in the ecosystem they live in
Black rhinoceros (Diceros bicornis)
White rhinoceros (Ceratotherium simum)
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Conceptual definition by George E. Hutchinson (1957):
A hypervolume set in an n-dimensional space where each of the axes represents an environmental parameter
Cold Spring Harbor symposia on quantitative biology 22: 415-427
What’s an ecological niche?
Temperature
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Conceptual definition by George E. Hutchinson (1957):
A hypervolume set in an n-dimensional space where each of the axes represents an environmental parameter
Cold Spring Harbor symposia on quantitative biology 22: 415-427
What’s an ecological niche?
Temperature
Salin
ity
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Conceptual definition by George E. Hutchinson (1957):
A hypervolume set in an n-dimensional space where each of the axes represents an environmental parameter
Cold Spring Harbor symposia on quantitative biology 22: 415-427
What’s an ecological niche?
Temperature
Salin
ity
![Page 7: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/7.jpg)
Conceptual definition by George E. Hutchinson (1957):
A hypervolume set in an n-dimensional space where each of the axes represents an environmental parameter
Cold Spring Harbor symposia on quantitative biology 22: 415-427
What’s an ecological niche?
Temperature
Salin
ity
2 categories of dimensions: habitat- and resource-related
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Conceptual definition by George E. Hutchinson (1957):
A hypervolume set in an n-dimensional space where each of the axes represents an environmental parameter
Cold Spring Harbor symposia on quantitative biology 22: 415-427
What’s an ecological niche?
Temperature
Salin
ity
2 categories of dimensions: habitat- and resource-related
Trophic niche = part of the ecological niche built using the subset of dimensions related to trophic resources
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Cold Spring Harbor symposia on quantitative biology 22: 415-427
What’s an ecological niche?
Niche axis B
Nic
he
axis
A
Fundamental niche: full range of conditions and resources in which an organism could survive and reproduce if free of any interference
Realized niche: narrower space that an organism is "forced" to occupy as a result of interactions with other species
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Cold Spring Harbor symposia on quantitative biology 22: 415-427
What’s an ecological niche?
Niche axis B
Nic
he
axis
A
Fundamental niche
Realized niche
Importance of competition as a driving mechanism
Kevin Ebi - http://livingwilderness.blogspot.com
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Identify ecological strategies: amount of resources and habitats used by animals (narrow vs. wide niches)
AB
Ecological niche study: why?
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Identify ecological strategies
Understand how ecological interactions can affect community structure
Niche overlap
A
B
A
BBA
Ecological niche study: why?
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Identify ecological strategies
Understand how ecological interactions can affect community structure
Competition
Niche overlap
A
B
A
BBA
Ecological niche study: why?
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Identify ecological strategies
Understand how ecological interactions can affect community structure
Highlight ecological shifts and study ecological plasticity
A
Condition 1
A
Condition 2
A
Condition 3
Ecological niche study: why?
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Identify ecological strategies
Understand how ecological interactions can affect community structure
Highlight ecological shifts and study ecological plasticity
A
Condition 1
A
Condition 2
A
Condition 3
Powerful theoretical concept but practical use limited (complicated or impossible to provide direct quantitative estimates for niche parameters)
Development of ecological niche proxies, including methods based on stable isotope ratios
Ecological niche study: why?
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Ecological niche study: how?
Variance of stable isotope ratios in animal tissues can be used to compare trophicniches among species
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Ecological niche study: how?
Variance of stable isotope ratios in animal tissues can be used to compare trophicniches among species
The "isotopic niche" can provide quantitative information on both resource and habitat use by animals
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Typical SI analysis output : points in "δ-space"
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C (‰)
δ1
5N
(‰
)Ecological niche study: how?
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Typical SI analysis output : points in "δ-space"
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C (‰)
δ1
5N
(‰
)
Position of consumers in the δ-space is driven by
1) Differences in consumed resources (different preys can have different isotopic
compositions)
Ecological niche study: how?
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Typical SI analysis output : points in "δ-space"
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C (‰)
δ1
5N
(‰
)
Position of consumers in the δ-space is driven by
1) Differences in consumed resources (different preys can have different isotopic
compositions)
2) Differences in habitat used for foraging
(the same prey can have different isotopic
compositions in different habitats)
Ecological niche study: how?
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Typical SI analysis output : points in "δ-space"
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C (‰)
δ1
5N
(‰
)
Position of consumers in the δ-space is driven by
1) Differences in consumed resources (different preys can have different isotopic
compositions)
2) Differences in habitat used for foraging
(the same prey can have different isotopic
compositions in different habitats)
Ecological niche study: how?
Although it is often used as a proxy for the trophic niche, the isotopic niche is ALWAYS depicting niches axes related with both resource and habitat use
The relative importance of the two sets of axes depend on the studied system + the isotopic ratios used
More of a proxy for the "realized ecological niche"
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C (‰)
δ1
5N
(‰
)Layman metrics
Geometric approach (Layman et al., 07):
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Geometric approach (Layman et al., 07):
Fit a convex hull (i.e., the smallest possible surface
that encompasses all points) to the 2D data
This convex hull represents the isotopic niche of the
group of consumers (proxyfor their trophic niche)
δ13C (‰)
δ1
5N
(‰
)Layman metrics
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Set of descriptors based on convex hull
1) δ13C range
Proxy of the diversity of resources supporting the
consumers
Greater when more primary producers are important for the
community
Layman metrics
δ13C (‰)
δ1
5N
(‰
)
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Set of descriptors based on convex hull
1) δ13C range2) δ15N range
Proxy of the vertical trophic structure of the community
Greater when consumers belong to more "trophic levels"
Layman metrics
δ13C (‰)
δ1
5N
(‰
)
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Set of descriptors based on convex hull
1) δ13C range2) δ15N range3) Total area of the convex hull
Proxy of the total diversity of resources used by the
community
Layman metrics
δ13C (‰)
δ1
5N
(‰
)
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Set of descriptors based on convex hull
1) δ13C range2) δ15N range3) Total area of the convex hull4) Mean distance to centroid
Averaged measure of ecological diversity among consumers
Greater when many consumers have "extreme" isotopic ratios,
i.e. very specific ecological habits
Layman metrics
δ13C (‰)
δ1
5N
(‰
)
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Set of descriptors based on convex hull
1) δ13C range2) δ15N range3) Total area of the convex hull4) Mean distance to centroid5) Mean nearest neighbor distance
Overall density of point packing
High when consumers are more divergent in terms of ecological
niche
Low when ecological habits of consumers are similar
(ecological redundancy)
Layman metrics
δ13C (‰)
δ1
5N
(‰
)
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Set of descriptors based on convex hull
1) δ13C range2) δ15N range3) Total area of the convex hull4) Mean distance to centroid5) Mean nearest neighbor distance6) Standard deviation of nearest neighbor distance
Measures how evenly ecological diversity is
distributed among consumers
High when space is evenly filled, low when "high density
regions" are present
Layman metrics
δ13C (‰)
δ1
5N
(‰
)
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Set of descriptors based on convex hull
1) δ13C range2) δ15N range3) Total area of the convex hull4) Mean distance to centroid5) Mean nearest neighbor distance6) Standard deviation of nearest neighbor distance
Comprehensive set of complementary (and partly
redundant) tools that provide global information about the
ecological niche
Designed for study of whole communities, but can also be
used for populations
Layman metrics
δ13C (‰)
δ1
5N
(‰
)
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Other hull-based metrics
Isotopic diversity indices
Computed differently, but conceptually similar to Laymanmetrics
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Other hull-based metrics
Layman metrics Isotopic diversity indices
Total area of the convex hull Isotopic richness
Mean distance to centroid Isotopic dispersion
Mean nearest neighbor distanceIsotopic divergence, Isotopic
uniqueness
Standard deviation of nearest neighbor distance
Isotopic evenness
Hull overlapIsotopic similarity, isotopic
nestedness
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Other hull-based metrics
Isotopic diversity indices
Computed differently, but conceptually similar to Laymanmetrics
Can be applied to more than 2 dimensions
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
Some hull-based metrics are highly sensitive to small sample size and to the presence of extreme points
According to your researchquestion, it can be a good or
a bad thing…
Ecological niche study: how?
δ13C (‰)
δ1
5N
(‰
)
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Standard ellipse vs. convex hull(SD vs. full range)
Represents "core isotopic niche" of the group of consumers
Main metric: standard ellipse area (SEA)
More robust and less sensitive to extreme values and small sample size (SEAc)
δ13C (‰)
δ1
5N
(‰
)
−12.5 −12.0 −11.5 −11.0 −10.5 −10.07
.27
.47.6
7.8
8.0
8.2
8.4
8.6
x
y
δ-space plots and standard ellipses
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Comparisons of groups
δ13C (‰)
δ1
5N
(‰
)
δ-space plots and standard ellipses
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Comparisons of groups
Quantification of isotopic niche overlap
δ13C (‰)
δ1
5N
(‰
)
δ-space plots and standard ellipses
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Comparisons of groups
Quantification of isotopic niche overlap
Ellipses and convex hulls can be complementary
δ13C (‰)
δ1
5N
(‰
)
δ-space plots and standard ellipses
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Lionfish (Pterois volitans/miles)
Native from Indo-Pacific regions
Isotopic niches: an example
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Lionfish (Pterois volitans/miles)
Native from Indo-Pacific regions
Data: USGS
Present in the Caribbean and US Atlantic waters since early 2000’s
Bahamas
Isotopic niches: an example
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Generalist predator ( > 40 fish species, benthic crustaceans)
Negative impact on prey populations
Isotopic niches: an example
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Generalist predator ( > 40 fish species, benthic crustaceans)
Negative impact on prey populations
Competition with native predators? Trophic niche overlap?
Schoolmaster snapper (Lutjanus apodus)
Grey snapper (Lutjanus griseus)
Isotopic niches: an example
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Isotopic biplot suggest important similarity in resource use
Isotopic niches: an example
![Page 44: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/44.jpg)
Isotopic biplot suggest important similarity in resource use
Convex hulls (proxy for the total, realized ecological niche) suggest overlap between the 3 species
Isotopic niches: an example
![Page 45: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/45.jpg)
Isotopic biplot suggest important similarity in resource use
Convex hulls (proxy for the total, realized ecological niche) suggest overlap between the 3 species
Standard ellipses (proxy for "core niche", i.e. most frequent utilization of resources): Competition is most likely to occur between lionfish and schoolmaster
Isotopic niches: an example
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Isotopic biplot suggest important similarity in resource use
Convex hulls (proxy for the total, realized ecological niche) suggest overlap between the 3 species
Standard ellipses (proxy for "core niche", i.e. most frequent utilization of resources): Competition is most likely to occur between lionfish and schoolmaster
Supported by gut contents: grey snappers ingest more benthic crustaceans
Isotopic niches: an example
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Instead of calculating SEA from covariance matrix: estimation using bayesian inference
More robust + takes uncertainty into account
δ13C (‰)
δ1
5N
(‰
)
δ-space plots and standard ellipses
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Stan
dar
d e
llip
se a
rea
(‰2)
01
23
4
Group
Are
a (
pe
rmil^
2)
1 2
Instead of calculating SEA from covariance matrix: estimation using bayesian inference
More robust + takes uncertainty into account
Outputs: frequency distribution of model solutions
Statistical comparisons of SEA across groups
δ-space plots and standard ellipses
![Page 49: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/49.jpg)
Stan
dar
d e
llip
se a
rea
(‰2)
01
23
4
Group
Are
a (
pe
rmil^
2)
1 2
Instead of calculating SEA from covariance matrix: estimation using bayesian inference
More robust + takes uncertainty into account
Outputs: frequency distribution of model solutions
Statistical comparisons of SEA across groups
δ-space plots and standard ellipses
106 solutions
SEA1 < SEA2 in 98.14 %
P-value analogy
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Iphimediidae in the Southern Ocean: widely distributed and common family with highecological diversity
Source: www.natuurwetenschappen.be/amphi/
Example: Iphimediidae amphipods
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Iphimediidae in the Southern Ocean: widely distributed and common family with highecological diversity
In the framework of vERSO and RECTO: Understand how environmental conditions caninfluence ecological features: comparison between West Antarctic Peninsula (WAP)and Adélie Land (AL)
Source: www.natuurwetenschappen.be/amphi/
Example: Iphimediidae amphipods
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Iphimediidae in the Southern Ocean: widely distributed and common family with highecological diversity
In the framework of vERSO and RECTO: Understand how environmental conditions caninfluence ecological features: comparison between West Antarctic Peninsula (WAP)and Adélie Land (AL)
Collaboration with RBINS (Marie Verheye & Cédric d’Udekem d’Acoz). Measurementsmade on abdominal legs (pleopods) of museum specimens
Source: www.natuurwetenschappen.be/amphi/
Example: Iphimediidae amphipods
![Page 53: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/53.jpg)
Common species only (Nspecies = 11, Nindividuals = 145)
Example: Iphimediidae amphipods
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Common species only (Nspecies = 11, Nindividuals = 145)
Example: Iphimediidae amphipods
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Common species only (Nspecies = 11, Nindividuals = 145)
Example: Iphimediidae amphipods
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Is assemblage niche larger in Western Antarctic Peninsula than in Adélie Land?
Example: Iphimediidae amphipods
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Is assemblage niche larger in Western Antarctic Peninsula than in Adélie Land?
Total niche: Yes (99.84% of model runs)
Tota
l are
a o
f th
e co
nve
x h
ull
(‰²)
Example: Iphimediidae amphipods
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Is assemblage niche larger in Western Antarctic Peninsula than in Adélie Land?
Total niche: Yes (99.84% of model runs)
Core niche: Yes (99.97% of model runs)
Tota
l are
a o
f th
e co
nve
x h
ull
(‰²)
Example: Iphimediidae amphipods
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Is assemblage niche larger in Western Antarctic Peninsula than in Adélie Land?
Total niche: Yes (99.84% of model runs)
Core niche: Yes (99.97% of model runs)
Iphimediidae amphipods exploit more resources in WAP than in AL
Tota
l are
a o
f th
e co
nve
x h
ull
(‰²)
Example: Iphimediidae amphipods
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Is this trend of wider isotopic niche found at the species level?
Example: Iphimediidae amphipods
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Is this trend of wider isotopic niche found at the species level?
Gnathiphimedia sexdentata: Yes Trend present in 99.56% of model solutions
Image source: d’Udekem d’Acoz & Verheye 2013
Example: Iphimediidae amphipods
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Is this trend of wider isotopic niche found at the species level?
Echiniphimedia echinata: No Trend present in only 80.64% of model solutions
Image source: Coleman 2007
Example: Iphimediidae amphipods
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Is this trend of wider isotopic niche found at the species level?
Echiniphimedia echinata: No Trend present in only 80.64% of model solutions
Image source: Coleman 2007
Species-specific patterns of ecological plasticity among amphipod assemblage
Example: Iphimediidae amphipods
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Is niche overlap between close species the same in both regions?
Coleman 2007
d’Udekem d’Acoz & Verheye 2013
Echiniphimedia echinataand
Echiniphimedia hodgsoni
Example: Iphimediidae amphipods
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Is niche overlap between close species the same in both regions?
Coleman 2007
d’Udekem d’Acoz & Verheye 2013
Echiniphimedia echinataand
Echiniphimedia hodgsoni
Example: Iphimediidae amphipods
![Page 66: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/66.jpg)
Is niche overlap between close species the same in both regions?
Coleman 2007
d’Udekem d’Acoz & Verheye 2013
Echiniphimedia echinataand
Echiniphimedia hodgsoni
Relative niche overlap: 42% of cumulative niche area
Relative niche overlap: 20% of cumulative niche area
Example: Iphimediidae amphipods
![Page 67: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/67.jpg)
Is niche overlap between close species the same in both regions?
Coleman 2007
d’Udekem d’Acoz & Verheye 2013
Echiniphimedia echinataand
Echiniphimedia hodgsoni
Example: Iphimediidae amphipods
OverlapWAP > OverlapAL
Probability = 99.00%
![Page 68: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/68.jpg)
Is niche overlap between close species the same in both regions?
Coleman 2007
d’Udekem d’Acoz & Verheye 2013
Echiniphimedia echinataand
Echiniphimedia hodgsoni
Relative niche overlap: 42% of cumulative niche area
Relative niche overlap: 20% of cumulative niche area
Niche overlap bigger in WAP Greater risk of interspecific competition
Example: Iphimediidae amphipods
![Page 69: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/69.jpg)
New metrics :
Eccentricity (deviation from circular shape) : eEstimating relative contributions of each axis to isotopic niche size
Other ellipse-based metrics
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θ
New metrics :
Eccentricity (deviation from circular shape) : eEstimating relative contributions of each axis to isotopic niche size
Angle between major axis and x-axis: θUnderstand which axis drives the variability in isotopic niche size
Other ellipse-based metrics
![Page 71: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/71.jpg)
θ
New metrics :
Eccentricity (deviation from circular shape) : eEstimating relative contributions of each axis to isotopic niche size
Angle between major axis and x-axis: θUnderstand which axis drives the variability in isotopic niche size
Relate isotopic niche parameters to specific ecological processes (trophic levelchange, resource shift, etc.)
Other ellipse-based metrics
![Page 72: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/72.jpg)
SIBER (Stable Isotope Bayesian Ellipses in R): R package, freely available from the CRAN repository
Allows Fitting of convex hulls and standard ellipses to isotopic data Computation of hull- and ellipse-based metrics Overlap calculations Model estimations of these parameters and statistical comparisons …
Example scripts: https://cran.r-project.org/web/packages/SIBER/vignettes/More info & help: https://github.com/AndrewLJackson/SIBER
SIBER R package
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Input data requirements
SIBER R package
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Input data requirements• 2 continuous variables
• Stable isotope ratios, but also others• If more: a priori selection or ordination method (e.g.
PCA)
SIBER R package
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Input data requirements• 2 continuous variables
• Groups or modalities to compare• e.g. compare different populations of a species
sampled in different zones and/or years, or differentspecies living together
• Spatial and temporal scope of the comparisons canbe adapted to the question
SIBER R package
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Input data requirements• 2 continuous variables
• Groups or modalities to compare
• Sufficient replication for each group• minimum n = 6• 10-12 points (or more) provide better results
SIBER R package
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Input data requirements• 2 continuous variables
• Groups or modalities to compare
• Sufficient replication for each group
Output data• Geometric approach: unique values
• Total or core niche width (TA, SEAc), niche overlap• Easy to handle and feed to other models (e.g. trait
distribution models)
SIBER R package
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Input data requirements• 2 continuous variables
• Groups or modalities to compare
• Sufficient replication for each group
Output data• Geometric approach: unique values
• Bayesian approach: large sets of model solutions• More robust but not so easy to handle• Possible solution: work with percentiles of
probability density function distributions
SIBER R package
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Multi-dimensional niche analysis
Other methods able to deal withmultiple (i.e., >2) dimensions exist
![Page 80: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/80.jpg)
The isotopic niche is a proxy! It is influenced by both resource and habitat use. Relative importance of those two drivers is case-dependent. Know your system.
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C
δ15N
Caution on isotopic niche
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The isotopic niche is a proxy! It is influenced by both resource and habitat use. Relative importance of those two drivers is case-dependent. Know your system.
The isotopic niche is a proxy! Its resolution is limited. It only pictures adequately ecological phenomena that significantly influence stable isotope ratios. It will be insensitive to many others
(e.g. diet shift between two prey that have similar isotopic compositions).
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C
δ15N
Caution on isotopic niche
![Page 82: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/82.jpg)
The isotopic niche is a proxy! It is influenced by both resource and habitat use. Relative importance of those two drivers is case-dependent. Know your system.
The isotopic niche is a proxy! Its resolution is limited. It only pictures adequately ecological phenomena that significantly influence stable isotope ratios. It will be insensitive to many others
(e.g. diet shift between two prey that have similar isotopic compositions).
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C
δ15N
Although not necessary, isotopic data on food sources can help avoiding interpretation mistakes: adapt your sampling strategies.
Caution on isotopic niche
![Page 83: Stable isotopes as descriptors of ecological niches · 2019. 1. 21. · Condition 1 A Condition 2 A Condition 3 Powerful theoretical concept but practical use limited (complicated](https://reader036.fdocuments.in/reader036/viewer/2022062311/5fe1985af0d78405b922a1b4/html5/thumbnails/83.jpg)
The isotopic niche is a proxy! It is influenced by both resource and habitat use. Relative importance of those two drivers is case-dependent. Know your system.
The isotopic niche is a proxy! Its resolution is limited. It only pictures adequately ecological phenomena that significantly influence stable isotope ratios. It will be insensitive to many others
(e.g. diet shift between two prey that have similar isotopic compositions).
−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C
δ15N
Although not necessary, isotopic data on food sources can help avoiding interpretation mistakes: adapt your sampling strategies.
Avoid simplistic interpretations. Niche overlap does not necessarily mean competition. Large isotopic niche does not necessarily mean generalist consumer.
Caution on isotopic niche
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C
δ15N
"Remember that all models are wrong; the practical question is how wrong do they have to be to not be useful."
George E.P. Box1919-2013
Caution on isotopic niche use
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−12.5 −12.0 −11.5 −11.0 −10.5 −10.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
x
y
δ13C
δ15N
Isotopic niche study is a rapidly evolving field supported by many different approaches and
concepts
When used sensibly, it is a robust and widely applicable method that can help solving many ecological questions linked with
resource partitioning among consumers
"Remember that all models are wrong; the practical question is how wrong do they have to be to not be useful."
George E.P. Box1919-2013
Caution on isotopic niche use
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Thanks for your attention
Images: Kevin Ebi - http://livingwilderness.blogspot.com. Full sequence: https://vimeo.com/272024913