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Relationships of Habitat Patch Size to Predator Community and Survival of Duck Nests

Tables


Table 1. Characteristics of small or large habitat patchesa studied in the Prairie Pothole Region of North Dakota, South Dakota, and Minnesota, 1993-95.
  1993 1994 1995
Small
n = 32
Large
n = 35
Small
n = 36
Large
n = 35
Small
n = 37
Large
n = 37
Mean of X Range Mean of X Range Mean of X Range Mean of X Range Mean of X Range Mean of X Range
Perennial cover (ha)
36 6-101 578 107-1,789 48 5-101 593 106-2,342 48 4-101 588 106-2,342
  % CRP
86   49   82   46   84   48  
  % hayland
2   5   4   4   4   4  
  % grassland
10   41   12   47   11   45  
  % woodland
2   5   2   3   2   3  
Wetlandb (ha)
7 0-105 155 1-596 12 0-118 121 4-468 11 0-118 118 4-468
Area past perimeterc (ha)
32   131 2-311 35 26-42 117 11-287 33 26-40 117 7-287
a Patch was composed of all adjoining tracts of Perennial Cover (grassland, hayland, planted cover, woodland, and land enrolled in the Conservation Reserve Program) that shared a common side, and temporary and seasonal wetlands located within the Perennial Cover. Patch size based on area of Perennial Cover: small patch = ≤105 ha, large patch >105 ha.
b Includes only seasonal and temporary basins within Perennial Cover.
c Study area was 41.4 km². Area of Perennial Cover contiguous with patches that abutted the perimeter of a study area was estimated to a distance of 0.8 km from perimeter. Number of patches beyond perimeter for small and large patches respectively, was 1 and 24 in 1993, 4 and 28 in 1994, and 3 and 30 in 1995.

Table 2. Results of analysis of variance on daily survival rates of upland duck nests in the Prairie Pothole Region of Minnesota, North Dakota, and South Dakota in relation to patch sizea, location (northwest or southeast of 46°8'N and 97°43'W), nest initiation dateb (early or late), and year (1993, 1994, or 1995).
Source df F P
Patch size
1,80 4.46 0.038
Location
1,80 0.39 0.536
Patch size × location
1,80 3.02 0.086
Initiation date
1,100 5.22 0.024
Initiation date × location
1,100 1.52 0.221
Initiation date × patch size
1,100 0.14 0.714
Initiation date × patch size × location
1,100 0.02 0.902
Yr
2,80 2.01 0.140
Yr × patch size
2,80 0.07 0.936
Yr × location
2,80 0.45 0.639
Yr × patch size × location
2,80 0.59 0.556
Yr × initiation date
2,58 3.79 0.028
Yr × initiation date × patch size
2,58 3.37 0.041
Yr × initiation date × location
2,58 1.03 0.362
Yr × initiation date × patch size × location
2,58 1.22 0.302
a Patch defined as in Table 1.
b Early and late nests were partitioned by median nest initiation date each year. Early nests were initiated on or before 1 June in 1993, and 7 June in 1994 and 1995; late nests were initiated after those dates.

Table 3. Numbers of nests, exposure days, and least-squares means estimates of daily survival rate of upland duck nests in the Prairie Pothole Region of Minnesota, North Dakota, and South Dakota relative to year × nest initiation datea (early or late) × patch sizeb interaction (F2,49 = 5.86, P < 0.01). Within categories early or late for each year, statistical differences (*) between patch sizes are based on Fisher's protected LSD procedure (P ≤ 0.05).
Yr Patch
size
Number of nests Exposure days Daily survival rate
Early Late Early Late Early Late
Estimate SE Estimate SE
1993 Small 79 116 849 1,444 0.924 0.014 0.943 0.010
Large 294 248 3,515 3,181 0.937 0.008 0.950 0.007
1994 Small 174 151 2,162 3,467 0.930 0.007 0.949 0.007
Large 289 280 2,051 3,468 0.944 0.006 0.954 0.006
1995 Small 231 231 3,028 5,080 0.950 0.006   0.937* 0.006
Large 400 380 2,554 4,920 0.952 0.006   0.962* 0.006
a Early and late nest initiation dates defined as in Table 2.
b Patch defined as in Table 1.

Table 4. Results of analysis of variance on predator activity indices in the Prairie Pothole Region in Minnesota, North Dakota, and South Dakota in relation to patch sizea, location (northwest or southeast of 46°8'N and 97°43'W), and year (1993, 1994, 1995).
Source df Red fox Coyote Striped skunk American badger Franklin's ground squirrel
F P F P F P F P F P
Patch size 1,117 4.11 0.045 1.88 0.173 0.49 0.485 0.01 0.909 0.02 0.886
Location 1,117 0.01 0.906 4.49 0.036 1.09 0.300 1.48 0.226 14.78 <0.001
Patch size × location 1,117 0.52 0.470 0.03 0.862 0.34 0.560 0.46 0.500 0.30 0.587
Yr 2,81 2.24 0.113 4.93 0.010 17.38 <0.001 6.44 0.003 2.82 0.066
Yr × patch size 2,81 2.05 0.135 0.20 0.817 0.16 0.853 0.67 0.693 0.65 0.527
Yr × location 2,81 5.33 0.007 0.12 0.891 0.36 0.701 0.78 0.463 0.07 0.929
Yr × patch size × location 2,81 0.37 0.691 4.07 0.021 1.31 0.276 1.49 0.232 0.85 0.431
a Patch defined as in Table 1.

Table 5. Correlation coefficients between daily survival ratesa (DSR) of upland duck nests in the Prairie Pothole Region of Minnesota, North Dakota, and South Dakota, and between explanatory variables, 1993-95.
  nb DSR
(late)c
Patch
locationd
Patch
sizee
Activity indexf
Red fox Coyote Striped
skunk
American
badger
Franklin's
ground squirrel
DSR (early)
184 0.03 0.05 0.15 −0.06 0.21 0.02 −0.06   −0.01  
DSR (late)
182   0.02 0.19 −0.16 0.05 0.07 −0.07   −0.04  
Patch location
212     0.13 −0.02 0.14 0.02 −0.12   −0.30  
Patch size
212       −0.22 0.12 −0.07   −0.03   −0.01  
Red fox
212         −0.15   0.29 0.16 −0.03  
Coyote
212           0.21 0.08 0.12
Striped skunk
212             0.06 −0.01  
American badger
212               0.18
a Estimated by Mayfield method, as modified by Johnson (1979).
b Number of patch × year combinations; n = 154 for correlation of DSR (early) × DSR (late).
c Early and late nest initiation dates defined as in Table 2.
d Patch defined as in Table 1.
e Patch size = ln (ha).
f Mean proportion of plots around study fields that contained carnivore tracks during 3 annual surveys, or number of unique Franklin's ground squirrels captured per trap day in 4 24-hr periods (Sargeant et al. 1993, Sovada et al. 1995).

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