Ecological Archives A020-008-A4

Chad C. Jones, Steven A. Acker, and Charles B. Halpern. 2010. Combining local- and large-scale models to predict the distributions of invasive plant species. Ecological Applications 20:311–326.

Appendix D. Importance of habitat variables in model results.

TABLE D1. Importance of habitat variables in model results. Importance was assessed differently for different model types. LR: number of replicates in which the variable was retained after stepwise removal; values in parentheses are mean regression coefficients (and sign) among replicates. GARP: For each replicate model, we created 50 GARP models with each of the 12 habitat variables removed (600 models/replicate). We then used t tests to compare the accuracy (Sensitivity) of models that included the variable of interest (550 models/replicate) with those in which the variable was removed (50 models/replicate). Values are mean t statistics (and SEs) for the five replicates of each species. The magnitude of a positive mean t statistic reflected the degree to which a variable improved model accuracy. ENFA: mean loading on the first factor, indicating the difference in a variable for points representing species' occurrences and the median of the study area.

 

— Geranium —

— Hedera —

— Ilex —

Habitat variable

LR

GARP

ENFA

LR

GARP

ENFA

LR

GARP

ENFA

Intercept

(25.56)

-

-

(66.62)

-

-

(90.58)

-

-

Annual precipitation

5
(-0.06)

-0.03
(0.32)

-0.55

 

-0.44
(1.99)

-0.57

4
(0.07)

0.40
(1.40)

-0.55

Conifer cover

5
(-0.19)

-0.05
(0.35)

-0.25

 

0.85
(0.67)

-0.07

 

0.33
(0.32)

-0.09

Distance to water

5
(-0.73)

-0.32
(0.31)

-0.30

 

0.13
(1.05)

-0.08

 

0.82
(0.51)

-0.09

Frost days

5
(0.06)

-0.62
(0.91)

-0.30

5
(-0.36)

1.86
(1.16)

-0.45

5
(-0.43)

-1.59
(2.57)

-0.41

Heat load

 

-0.80
(0.19)

-0.10

 

0.73
(0.85)

-0.01

 

-0.67
(1.28)

-0.08

Potential radiation

1
(-2.25)

-0.67
(0.33)

-0.08

1
(18.94)

-0.51
(2.37)

0.01

 

-1.69
(0.90)

-0.07

Precipitation frequency

5
(34.9)

2.14
(0.76)

-0.48

 

-0.05
(1.37)

-0.24

5
(-84.5)

2.71
(0.75)

-0.30

Radiation

5
(-2.61)

-0.86
(0.43)

0.01

5
(-4.05)

-1.53
(2.30)

0.13

5
(-3.20)

0.94
(0.33)

0.11

Slope

 

-1.18
(0.59)

-0.31

 

0.13
(0.41)

-0.40

 

-3.77
(3.05)

-0.45

Vegetation cover

 

-0.79
(0.33)

-0.08

 

-0.01
(0.57)

-0.22

 

-0.46
(0.45)

-0.07

Humidity

5
(0.002)

1.43
(0.33)

0.14

 

-1.37
(1.84)

0.32

5
(-0.004)

-0.65
(0.84)

0.28

Topographic moisture index

 

0.59
(0.44)

0.30

 

-0.83
(2.09)

0.22

 

0.39
(0.60)

0.27

Marginality

-

-

1.17

-

-

1.02

-

-

1.02

Specialization

-

-

2.07

-

-

6.24

-

-

4.39

Residual deviance

189.66

-

-

15.09

-

-

27.21

-

-
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