WETLANDS. Vol. 13, No. 4, December 1993, pp. 260-269 ~3 1993, The Soeiely of Wetland Scientists
DISTRIBUTION AND ABUNDANCE OF AQUATIC MACROINVERTEBRATES FOLLOWING DROUGHT IN THREE PRAIRIE POTHOLE WETLANDS Karen j. Bataille ~ and Guy A. Baldassarre
Environmental and Forest Biology State University of New York College of Environmental Science and Forestry Syracuse, N Y 13210 Abstract: We collected aquatic macroinvertebrates in a seasonal, semipermanent, and permanent pothole
wetland in southwestern Manitoba, Canada to determine their abundance and distribution following drought in relation to the prelaying, egg-laying and brood-rearing periods of canvasbacks (Aythya valisineria). We collected 26 taxa ofnektonic macroinvertebrates of which 6 major groups (Cladocera, Copepoda, Ostracoda, Culicidae, D,ytiscidae, Gastropoda) collectively comprised >98% of the total number of individuals. The number of nektonic macroinvertebrates peaked during the egg-laying period, and crustaceans were the most abundant taxa in all 3 potholes during all 3 breeding periods. We collected 50 families of emergent insects and several unknown families in the orders Coleoptera and Diptera. Five major groups (Chironomidae, Culicidae, other Diptera, Coleoptera, Leptoceridae) coUectively comprised > 97% of the total number. Insect emergence increased during the breeding season to a peak during the brood-rearing period. Chironomids were the most abundant emergent insect during all 3 breeding periods and were most abundant in the permanent pothole. Chironomids collected on artificial substrates also were most abundant in the permanent pothole during all 3 breeding periods. The number of gastropods was greatest during the laying and broodrearing periods. Following drought, it appeared that macroinvertebrates were abundant and widely distributed in the 3 potholes.
Key Words: Aythya vafisineria, Canvasback, drought, invertebrates, Manitoba, prairie potholes, wetlands.
INTRODUCTION
protein necessary for growth and reproduction because invertebrates generally have a much higher protein content than plants (Driver et al. 1974). Indeed, Krapu (1979) showed adverse effects on clutch size and egg hatchability in captive mallards (Anas pfatyrhynchos Linnaeus) when denied access to animal foods. The capacity o f prairie potholes to produce invertebrates is largely due to the dynamic nature of these systems, which is influenced by annual moisture regimes and long-term trends in climatic conditions', drought is common (Kantrud et al. 1989, Swanson and Duebbert 1989). These trends cause extreme fluctuations in water levels that flood and dry pothole basins. Drought has dramatic effects on aquatic invertebrates. For example, fairy shrimp (Anostraca) and seed shrimp (Ostracoda) inhabit seasonal and semipermanent potholes and can withstand annual drying, whereas water bugs (Hemiptera) are true emigrants because they can fly to a more suitable habitat (Mackay 1984). Some invertebrates such as scuds (Amphipoda) require water throughout the year, which restricts them to more permanent water habitats (Pennak 1978, Wiggins et al. 1980). Although drought is common in the prairie pothole
The prairie pothole region encompasses approximately 776,900 km 2 in the western plains of Canada and the United States and is characterized by numerous depressional wetlands (potholes) formed by the drift deposits of the Wisconsin glaciation (Batt el al. 1989). This region is considered the most important duck production habitat in North America because it can account for 50% of the annual production of ducks on the continent (Smith et al. 1964), and 20 of 34 species of ducks that breed in North America are present in the area (Batt et al. 1989). Much of the importance of the prairie pothole region to breeding ducks stems from the high biomass and secondary productivity of macroinvertebrates (hereafter invertebrates) in prairie potholes. Invertebrates are essential to adult and juvenile ducks during egglaying and brood-rearing (Swanson and Meyer 1973, Krapu 1974a, b, Swanson et al. 1974, Krapu and Swanson I975); they are c o n s u m e d by d u c k s to o b t a i n the ' Present Address: Missouri Department of Conservation, Fish and Wildlife Research Office, 1110 South College Avenue, Columbia, MO 65201
260
Bataille & Baldassarre, MACROINVERTEBRATES FOLLOWING D R O U G H T region and dramatically affects the availability of invertebrates to vertebrate predators such as ducks (Murkin and Batt 1987), the distribution and abundance of invertebrate families following drought is poorly known. This is significant because recovery of invertebrate populations after drought would seem to be an essential prerequisite to recovery of waterfowl production. Further, little work has been done on the systematics or ecology of invertebrates occupying different types of prairie potholes, yet this system comprises one of the world's largest freshwater wetland complexes (Murkin 1989). Our objective was to document the distribution and abundance of invertebrate families occupying 3 different types of prairie pothole wetlands immediately following drought, and relate these data to the prelaying, egg-laying, and brood-rearing periods of canvasbacks (Aythya valisineria Wilson). STUDY AREA AND METHODS This study was conducted at the Delta Waterfowl and Wetlands Research Station Study Area near Minnedosa, Manitoba, an area in southwestern Manitoba that is primarily agricultural and has been described in detail by Stoudt (1982). This 13-week study began at ice-melt (23 April 1990) and continued until water levels became too shallow (<10-15 cm) to operate activity and artificial substrate traps (21 July). Precipitation in 1989 was 73% of average, with 33.4 cm recorded at Brandon, Manitoba, which was 32 km south of our study wetlands (Figure 1). Since below-average precipitation occurred from 1987 to 1989 and canvasbacks did not reproduce in the Minnedosa area during 1989 (M.G. Anderson, Delta Waterfowl and Wetlands Research Station, personal communication), we defined 1989 as a drought year. During 1990, precipitation was 123% of average, with 55.4 cm recorded at Brandon. Precipitation at our study site was 3.5 cm from 23-30 April, 6.4 cm in May, 7.0 cm in June, and 5.1 cm from 1-21 July. The 3 prairie potholes we studied were classified as seasonal, semipermanent, and permanent (Stewart and Kantrud 1971). Due to fiscal and logistical constraints, our sampling was limited to one pothole of each type, and our interpretations of results are meant to apply to those individual wetlands only (Wester 1992). The 3 potholes were selected because they represent common types of pothole wetlands that are used heavily by ducks for feeding, nesting, and brood-rearing (Stewart and Kantrud 1973, Dwyer et. al 1979, Duebbert and Frank 1984). The potholes were located within an agricultural field and separated by 250-350 m. The field was planted with barley on 11 May and pesticides (i.e., herbicides and insecticides) were not applied to the adjacent or surrounding crops. This was an ira-
261
60
~'
E • ~)
G)
~"
Average
45
50,-
cm
40'
<
30
80
8'2
8'4
S'6
'-
6'8
90
Year Figure 1.
Annual precipitatien at Brandon, Manitoba from
1980 through 1990.
portant consideration because application of pesticides can dramatically reduce populations of aquatic invertebrates (Grue et al. 1988). The permanent pothole basin was 2.5 ha in area, with a narrow band (1-10 m) of emergent vegetation ocularly estimated as a 50:50 mix of cattails (Typha spp.) and bulrushes (Scirpusspp.). The semipermanent basin was 1.1 ha in area; open water (50%) was surrounded by deep marsh vegetation (5-10 m) dominated by cattails (850/0) and bulrushes (15%) and an extensive band (10--20 m) of shallow marsh vegetation dominated by whitetop (Scolochtoafestucacea Willdenow). Submergent vegetation in open water was dominated by white water buttercup (RanuncuIus aquatilis Linnaeus), other buttercups (Ranunculus spp.), and water milfoil (Myriophyllum spp.). The seasonal pothole basin was 0.5 ha in area and dominated by whitetop and sedges (Carex spp.). In 1989, the seasonal pothole did not contain water and the semipermanent pothole was dry by 14 July; the permanent pothole did not dry completely (M.G. Anderson, Delta Waterfowl and Wetlands Research Station, personal communication). Our sampling scheme was designed to facilitate the collection and comparison of invertebrates within the major vegetational zones of each pothole type. Thus, in the semipermanent pothole, 5 sampling stations were selected randomly within each of 3 vegetational zones (shallow marsh, deep marsh, open water). In the permanent pothole, 5 sampling stations were selected randomly in the open water zone. In the seasonal pothole, 5 sampling stations were selected randomly in the shallow marsh zone. Each station consisted of a modified model 'week' emergence trap that had a basal area of 0.5 m 2 (LeSage and Harrison 1979), an activity trap (Murkin et al. 1983), and an artificial substrate trap (Ross and Murkin 1989). Invertebrates were collected weekly at each station;
262
WETLANDS, Volume 13, No. 4, 1993 I~. t-q ~O t'-,I C'-I
m ~
£
m<<< r-- ~'300
t'N
0
m(J<<
c5 c5 ~ ,~ ~q
~ c5 c5 c5
<<<<< V
~
<
V
0
0
0
V
VV
~
0
~
0
0
v v
0
s. O
A
6~
<<<<
>
--V
V
~
V e.
E
e-
~a¢5
II
°°I
m
-T 0
e-
<
V
~
~V
r~
o
b-
< < < ~ <
~
E=
~
O
~
¢)
.=-~
O
o.~
~rh
Bataille & Baldassarre, MACROINVERTEBRATES FOLLOWING D R O U G H T however, samples were not collected in the open water zones of the semipermanent and permanent potholes ill week 1 due to freezing temperatures and snow from 28-30 April. Due to low water levels, emergence trap samples were not collected in the shallow marsh zone after week 11, Similarly, activity trap samples were not collected in the shallow marsh after week 8 nor in deep marsh or the seasonal pothole after week 12. Artificial substrate samples were not collected in the shallow marsh after week 7 nor in the deep marsh and seasonal pothole after week 11. Emergence traps were used to index aquatic insect populations within potholes, and activity traps were used to index the population of nektonic invertebrates (Murkin et al. 1983). Each activity trap was set for a 24-hour period, after which the sample was collected by filtering through a #35 U.S. Standard sieve (500 micron). Artificial substrates were used 1o index snail (Gastropoda) and midge (Chironomidae) populations on submerged surfaces (Ross and Murkin 1989). All samples were sorted, counted, usually identified to the family level, and then placed in glass vials and preserved in 70% ethanol. When necessary, a mechanical subsampler was used to count large numbers of a single taxon (Ross and Murkin 1989). Identification of invertebrates and nomenclature followed Merritt and Cummins (1984), Pennak (1978), and Borror et al. (1989). Plant identification and nomenclature followed Fassett (1957). Although results could be presented in descriptive fashion, we employed inferential statistics to further elucidate differences between the 3 potholes. Data were analyzed using the Statistical Analysis System and followed an analytical strategy of a 3 breeding period × 5 pothole treatment factorial experiment; where appropriate, means were separated using the contrasts procedure (SAS Institute, Inc. 1989). The 3 breeding periods were defined by grouping weekly samples to coincide with the 1990 breeding cycle of canvasbacks, a common species of duck breeding on the Minnedosa study area. These periods were prelaying (weeks 1--4), laying (weeks 5-8), and brood-rearing (weeks 9-13) (Robert Emery, Delta Waterfowl and Wetlands Research Station, personal communication). The 5 pothole treatments were defined according to pothole type or vegetational zones within a pothole type. These treatments were (1) seasonal pothole, (2) permanent pothole, (3) shallow marsh zone, (4) deep marsh zone, and (5) open water zone. To make comparisons among potholes, we combined the shallow marsh, deep marsh, and open water zones to represent the semipermanent pothole; during brood-rearing, the semipermanent pothole was represented by the deep marsh and open water zones only. The main effects and interaction effects of breeding
263
Table 2. Nektonic macroinvertebrates collected in activity traps in 3 prairie potholes sampled in Southwestern Manitoba, 23 April-21 July 1990. Nematoda Gastropoda Physidae Lymnaeidae Planorbidae Annelida Hirudinea Eubranchiopoda Anostraca Cladocera Copepoda Ostracoda Amphipoda Talitridae Odonata Libellulidae Lestidae Coenagrionidae
Hemiptera Belostomatidae Corixidae Notonectidae Coleoptera Hal iplidae Dytiscidae Hydrophilidae Trichoplera Leptoceridae Diptera Chaoboridae Culicidac
Ceratopogonidae
Chironomidae Acarina Arrenuridae Hydrachnidae
period and pothole type were analyzed using overall invertebrate abundance as well as individual taxa abundance. Data were transformed to the log (X + 1) scale to stabilize variances. The traps used in this study were designed to differentially sample habitats as well as different life stages of some invertebrates; therefore, data were analyzed and results presented by trap type. RESULTS Nektonic Invertebrates We collected 26 families of nektonic invertebrates in activity traps and arranged them into 6 taxonomic groups: Cladocera, Copepoda, Ostracoda, Culicidae, Dytiscidae, and Gastropoda. These 6 groups collectively comprised >98% of the total number of invertebrates (Table 1); other taxa were grouped as miscellaneous (Table 2). There was no breeding period by pothole type interaction effect for overall invertebrate number (P > 0.15) (Figure 2); thus, data were analyzed for the main effects of breeding period and pothole type. However, there were interaction effects for individual taxa (P < 0.15), which then were analyzed for simple effects of pothole type within breeding periods. Nektonic invertebrates were most abundant in the semipermanent pothole (190-996/trap; P < 0.05) during all 3 breeding periods and comprised 54-73% of the total number collected in all 3 potholes. The mean total number of nektonic invertebrates was greatest during the laying period (722/trap; P < 0.05). Crustaceans (ostracods, copepods, cladocerans) were
264
WETLANDS, Volume 13, No. 4, 1993 during the brood-rearing period. Other taxa comprised 3% of the total number of nektonic invertebrates.
,,lUMBERS LOG(X-'l)
3.5
Emergent Insects 2.5
1.5 B p /
2,5
l
j
1; ~
0 l
~
_
m
J .
~
_
PRELAYING
z
~
-
-
-
-
Jow j
~
J
j
~
~
L
LAYING
BROODS
BREEDING PERIOD
Figure 2. ANOVA interaction effects of the mean number (Log x + 1) of (A) nektonic macroinvertebrates (No./trap/period) captured in activity traps and (B) emergent insects (No./ mVperiod) captured in emergence traps for each treatment. SM = shallow marsh, DM = deep marsh, OW = open water, P = permanent pothole, S = seasonal pothole. The semipermanent pothole is represented by the SM, DM, OW zones. (A) SE = 0.11, P = 0.25; (B) SE = 0.12, P = 0.0001. the most abundant nektonic invertebrates during all 3 breeding periods. Ostracods comprised 54-86% of all invertebrates collected and were by far the most abundant (P < 0.05) in the semipermanent pothole (121931/trap; 64-96%) (Table 1), The seasonal pothole had the second highest number of ostracods, which comprised 25-38% of all invertebrates collected. Cladocerans comprised only 5-10% of all invertebrates collected and were most abundant (P < 0.05) in the permanent pothole (35-318/trap) during all 3 breeding periods, where they comprised 41-77% of all invertebrates collected. Copepods comprised 7-31% of all invertebrates collected and 45-64% of the invertebrates collected in the seasonal pothole. Copepods were distributed widely among all 3 potholes during the prelaying and laying period but were most abundant (P < 0.05) in the seasonal and permanent potholes
In the emergence traps, we collected 50 families of insects and several unknown families in the orders Coleoptera and Diptera. These insects were arranged into 5 taxonomic groups: Chironomidae, Culicidae, other Diptera, Coleoptera, and Leptoceridae that comprised > 97% of the total number of insects collected (Table 3); others were grouped as miscellaneous (Table 4). Unlike the activity traps, there was a breeding period by pothole type interaction effect for total numbers of emergent insects (P < 0.15) (Figure 2); therefore, data were analyzed for the main effect of breeding period and simple effects of pothole type within breeding period. There were also interaction effects for number of individual taxa (P < 0.15), which therefore were analyzed for simple effects of potholes within periods. The mean total number of emergent insects increased throughout the breeding season and was greatest during brood-rearing (365/m2; P < 0.05) (Table 3). The mean total number of emergent insects was greatest (P < 0.05) in the permanent pothole during all 3 periods, ranging from 74 to 1,053/m 2 and comprising 58-80% of the total number collected in all 3 potholes. During all 3 periods, chironomids comprised 7178% of the total number of emergent insects. Except for the open water zone during brood-rearing, chironomids were most abundant in the permanent wetland (67-977/m 2) during all 3 periods, where they comprised 89-99% of the insects collected (Table 3). For culicidae, 99% (28-100/m 2) were collected in the shallow marsh and deep marsh zones during laying and brood-rearing. The mean number of other dipterans was greatest in the shallow marsh zone during laying (107/m 2) and brood-rearing (139/m:), where they comprised 66% and 64%, respectively, of all insects collected. During brood-rearing in the deep marsh zone, a mean of 84 other dipterans/m 2 emerged, which comprised 49% of all insects; 65/m 2 emerged from the seasonal pothole, where they comprised 83% of all insects. Leptocerids occurred only in the permanent pothole and comprised 10% o f the emergence during broodrearing. Other taxa comprised < 10% of the total number of emergent insects. Benthic Invertebrates Although other invertebrates were sampled, we collected only chironomids and gastropods on artificial substrates. There were breeding period by pothole type interaction effects for both chironomids (P < 0.15) and
Bataille & Baldassarre, MACROINVERTEBRATES FOLLOWING D R O U G H T
M
265
ddd~d
~d~d~
~
d
<<<<<
<<<<<
<
<<<<<
<<<~<
<<<~<
d
i
=_ 0 r~
0 0 0
<<<<<
~<<<<
m~<<~
~ o o o
~ o o o
& 0 0 0 0 ~
ooooo
@
0 A
V
m°V
mc~VVV
ddd~d
~dddd
0
ddddd
_-s
0
d
e-
V V V ~ V
e.-
--~--
~m~
E~
266
WETLANDS, Volume 13, No. 4, 1993
Table 4. Emergent insects collected in emergence traps in 3 prairie potholes sampled in Southwestern Manitoba, 23 April-21 July 1991. Collembola Ephcmeroptera Baetidae Ephemeridae Odonata Libellulidae Lestidae Coenagrionidae Hemiptera Saldidae Homoptera Cicadellidae Coleoptera Dytiscidae Staphylinidae Hydrophilidae Scirtidae Heiodidae Elmidae Coccinellidae Chrysomelidae Curculionidae Other Hymenoptera Braconidae Iehneumonidae Trichogrammatidae Diapriidae Scelionidae Pompilidae Other
Trichoptera Hydroptilidae Limnephilidae Phryganeidae Leptoceridae Lepidoptera Arctiidae Noctuidac Diptera Tipul~dae Psychodidae Dixidae Chaoboridae Culicidae Ceratopogonidae Chironomidae Tabanidae Stratiomyidae Empididae Dolichopodidac Phoridae Syrphidae Anthomyzidae Dryomyzidae Sciomyzidae Ephydridae Scathophagidae Muscidae Sarcophagidae Other
gastropods (P < 0.15); therefore, both taxa were analyzed for the main effect of period and simple effects of pothole type within breeding period. The mean number ofchironomids was greatest during the brood-rearing period (17/trap; P < 0.05). The mean number ofchironomids was greatest (P < 0.05) in the permanent pothole during all 3 breeding periods and rare or absent from all other zones except the open water zone during brood-rearing (14/trap) (Table 5). The mean number of gastropods was similar (P > 0.05) during the laying (5/trap) and brood-rearing (7/ trap) periods, which were greater than the number collected during the prelaying period (2/trap; P < 0.05). The numbers of gastropods in the semipermanent and permanent potholes were similar (P > 0.05) during all 3 breeding periods. Gastropods were rare in the seasonal pothole during the prelaying and laying periods; however, during brood-rearing, the mean number in the seasonal pothole (9/trap) was similar (P > 0.05) to the semipermanent (6/trap) and permanent (7/trap) potholes.
Table 5. Mean number (No./trap, n - 5) of Chironomidae and Gastropoda collected on arlificial substrates in prairie potholes sampled in Southwestern Manitoba. Chironomidae Prelaying Semi-permanent Shallow Deep Open Permanent Seasonal Laying Semi-permanent Shallow Deep Open Permanent Seasonal
Gastropoda
SE
.~
SE
0A"b 0A 0A 46B 0A
0.0 0.0 0.0 5.7 0.0
5A 1BC 3AC 2AB < 1B
1. t 0.2 0.8 0.6 0.1
0A 0A < IA 20B 0A
0.0 0.0 0.1 3.8 0.0
15B 3A 3A 5A < 1C
3.8 1.1 0.3 1.5 0.1
Brood-rearing Semi-permanent Shallow Deep 0A 0.0 2B 1.3 Open 14B 1.2 10A 1.3 Permanent 53C 5.5 7A 2.8 Seasonal 0A 0.0 9AB 5.5 Means in columnwithin breedingperiodswith the same lettersare not different(P > 0.05). Data analyzedusinglog(x + 1) transformation. DISCUSSION We did not have pre-drought data; thus, it is unknown to what extent abundance and diversity of invertebrates changed post-drought in the 3 potholes we sampled. However, the numbers of nektonic invertebrates and emerging insects we collected were comparable to or greater than numbers of invertebrates collected in other areas not recovering from drought. For example, using sampling equipment identical to ours, Murkin et al. (1991) found the number of nektonic invertebrates in 5-ha impoundments created within the Delta Marsh, on Lake Manitoba, to range from 0 to 100 per trap in cattail areas and 2 to 180 per trap in open water areas, We collected 286 to 2,094 per trap in the deep marsh and 73 to 411 per trap in open water areas. These numbers are not statistically comparable but suggest that recovery may have occurred in our wetlands since the Delta Marsh impoundments were similar in being isolated from the remainder of the marsh and contained cattail stands and open water. However, the water levels in the impoundments were maintained by a mechanical pump that eliminated the effects of dmwdown on invertebrates.
Bataille & Baldassarre, MACROINVERTEBRATES FOLLOWING DROUGHT
267
In wetlands in northwest Ohio, Riley and Bookhout (1990) collected 82-2,921 invertebrates per trap. These wetlands were separated from Lake Erie by dikes, were subject to moist soil management techniques including flooding and drawdown, and were dominated by nodding smartweed (Polygonum lapathifolium Linnaeus). The number of invertebrates collected using activity traps in these wetlands was similar to our sites and thus suggests recovery of invertebrates in our study wetlands. Again using identical equipment, the numbers of chironomids collected from open water areas at the Delta Marsh and nearby Bone Pile Pond (200-640/ m 2) (calculated from data in Wrubleski 1987, Wrubleski and Rosenberg 1990) were similar to the mean numbers (67-977/m 2) we collected in the permanent pothole and in the open water zone (< 1-296/m2). In contrast, we collected fewer chironomids (< 1--45/m 2) in the deep marsh zone than in the cattail zone of Bone Pile Pond (~84 and 302/m2). Our data also are related to the various droughtsurviving mechanisms employed by aquatic invertebrates in which at least one stage of the life cycle is adapted for survival (Mackay 1984). These mechanisms include emigration, retreat, resistance, and immigration and recolonization. Accordingly, Wiggins et al. (1980) classified invertebrates in temporary pools into 4 Groups according to their methods of surviving drought and their seasonal patterns of recruitment. Group 1 invertebrates are permanent residents capable of passive dispersal; they overwinter in stages resistant to desiccation or in bottom sediments. Group 2 invertebrates are capable of dispersal, oviposit on water in spring, and survive dry periods in various life stages. Group 3 invertebrates are also capable of dispersal, oviposition is independent of water, and eggs or larvae overwinter. Group 4 invertebrates are emigrants that leave a drying wetland, pass dry phases in permanent waters, and return to oviposit in newly flooded basins. Crustaceans, the most abundant group of nektonic invertebrates in all 3 potholes, are classified as Group 1 invertebrates. Crustaceans overwinter as eggs that are highly resistant to desiccation and hatch when basins are reflooded and suitable conditions for development are reached, which can explain why they occurred in high numbers at all sites. Noticeably, however, amphipods were absent from the semipermanent wetland, which may have occurred because they are drought sensitive (Pennak 1978, Wiggins et al. 1980). Alternatively, although no pesticides were used on fields
taceans is significant because they are important in the diet of breeding ducks such as northern shovelers (Anas clypeata Linnaeus) and blue-winged teal (.4. discors Linnaeus) (Swanson and Meyer 1973, Swanson et al. 1974). Additionally, since ducks can partition food resources by prey size as dictated b.y the density of bill lamellae (Nudds and Bowlby 1984), larger invertebrates such as Gastropoda, Culicidae, Leptoceridae, Chironomidae, and Dytiscidae are important to other species such as gadwalls (A. strepera Linnaeus), northern pintails (A. acuta Linnaeus), and canvasbacks (Bartonek and Hickey 1969, Krapu 1974b, Swanson et al. 1974). These larger taxa were present in all 3 potholes during one or all of the breeding periods. The gastropods we collected are pulmonate snails classified as Group 1 invertebrates (Wiggins et al. 1980). Juvenile and adult snails survive drought in a dormant state, secreting an epiphragm that covers their aperture and reduces moisture loss. We collected gastropods in the semipermanent and permanent potholes during all 3 breeding periods; however, they were rare in the seasonal pothole during prelaying and laying. Unlike the semipermanent and permanent potholes, the seasonal pothole did not contain water in 1989; hence, the absence of gastropods from this pothole in early 1990 may have been due to the extended dry period. Gastropods also may not withstand dry periods of more than 1 year or many may have died due to extended exposure to predation (Wiggins et al. 1980). In the culicid family, two common genera, (Aedes and Psorophora), are classified as Group 3 invertebrates (Wiggins et al. 1980). These occur in temporary ponds and pools (Newson 1984) and survive drought in the egg stage. Other genera such as Anopheles and Cutex overwinter as adults and deposit their eggs on the water surface in spring. The reason for the conspicuous lack of culicids in the seasonal pothole is unclear because seasonal potholes are among the first to thaw in the spring, and culicids are among the earliest colonizers (Wiggins el al. 1980). Hence, it seems unlikely that drought was a major contributing factor, but we only sampled one seasonal pothole. Chironomids are an extremely diverse group of aquatic insects classified as Group 2, 3, and 4 invertebrates (Wiggins et al. 1980, Coffman 1984). Only the predacious Tanypodinae are classified as Group 4, and they overwinter in the adult stage. Group 2 and 3 chironomids survive drought and/or overwinter as larvae in the sediments (Wiggins et al. 1980). Chironomid
study, amphipods are extremely sensitive to the residual effects of pesticides that may have been used in prior years (Grne et at. 1988). Regardless, such high numbers and early appearance of other species ofcrus-
potholes to permanent potholes and is dependent on factors such as wetland morphometry and water chemistry (Driver 1977). Since we did not identify invertebrates past the family level, we were unable to de-
s u r r o u n d i n B the s e m i p e r m a n e n t p o t h o l e d u r i n g our
species diversRy also m a y increase f r o m t e m p o r a r y
268
WETLANDS, Volume 13, No. 4, 1993
termine chironomid species diversity. However, the number of chironomids we collected increased from the seasonal to permanent pothole. In addition, chironomid emergence from the semipermanent pothole during prelaying averaged < l/m 2, while emergence from the permanent pothole averaged 67/m 2. Since many species ofchironomids are multivoltine (Merritt and Cummins 1984), the gradual increase of chironomids in the semipermanent pothole during the breeding season may thus represent immigration ofchironomids from more permanent potholes. The peak of emergent insects such as chironomids during the brood-rearing period is important because emerging insects are an important food source for ducklings (Chura 1961, Collias and Collias 1963, Sugden 1973, Sj6berg and Danell 1982, Jarvis and Noyes 1986). Young ducklings such as mallards and bluewinged teal are adept at catching flying insects and rely on surface feeding for 1-2 weeks after hatching, whereas diving ducks may begin diving sooner (Collias and Collias 1963). Although Bartonek and Hickey (1969) rarely encountered flying forms of insects in the food contents of diving ducks, they observed ducklings consuming insect pupae as they rose to the surface of the water to emerge. In addition, nighttime feeding of ducks seems correlated with the time and intensity of insect emergence (Swanson and Sargeant 1972, Swanson and Meyer 1973, Danell and Sj6berg 1977). Invertebrates were abundant and widely distributed in the 3 potholes and thus potentially showed rapid recovery following drought. Overall, invertebrate taxa and numbers within taxa varied among the 3 potholes; this was probably due to several factors, including invertebrate drought-survival mechanisms, water chemistry, and wetland morphometry. However, to expand our information will require further study of invertebrates within a larger number and type of prairie potholes before, during, and following drought. ACKNOWLEDGMENTS We thank the North American Wildlife Foundation, Delta Waterfowl and Wetlands Research Station, and the State University of New York, College of Environmental Science and Forestry. for funding this project. We are especially grateful to H.R. Murkin for assistance throughout the study and D.B. Wester for advice with statistical analyses. N.H. Ringler and F.E. Kurczewski reviewed early drafts of the manuscript. LITERATURE
CITED
Bartonek, J.C. and J.J. Hickey. 1969. Food habits of canvasbacks, redheads, and lesser scaup in Manitoba. Condor 71: 280-290. Ball, B.D.J., M.G. Anderson, C.D. Anderson, and F.D. Caswell. 1989. The use of prairie potholes by North American ducks, p.
204-227. In A. van der Valk (ed.) Northern Prairie Wetlands. Iowa State University Press, Ames, IA, USA. Borror, D.J., C.A. Tdplehorn, and N F . Johnson. 1989. An Introduction to the Study of Insects. Sixth Edition. Saunders College Publishing, Philadelphia, PA, USA. Chura, N.J. 1961. Food availability and preferences of juvenile mallards. Transactions of the North American Wildlife and Natural Resources Conference 26:121-134. Coffman, W.P. 1984. Chironomidae. p. 551-652. In R.W. Merritt and K.W. Cummins (eds.) An Introduction to the Aquatic Insects of North America, Second Edition. Kendall/Hunt Publishing Company, Dubuque, IA, USA. Collias, N.E. and E.C. Collias. 1963. Selective feeding by wild ducklings of different species. Wilson Bulletin 75: 6-14. Danell, K. and K. Sj/Sberg. 1977. Seasonal emergence of chirondruids in relation to egglaying and hatching of ducks in a restored lake (northern Sweden). Wildfowl 28:129-i 35. Driver, E.A. 1977. Chironomid communities in small prairie ponds: some characteristics and controls. Freshwater Biology 7:121-133. Driver, E.A., L.G. Sugden, and R.J. Kovach. 1974. Calorific, chemical and physical values of potential duck foods. Freshwater Biology 4: 281-292. DuebberI, H.F. and A.M. Frank. 1984, Value of prairie wetlands to duck broods. Wildlife Society Bulletin 12: 27-34. Dwyer, T.J., G.L. Krapu, and D.M. Janke. 1979. Use of prairie pothole habitat by breeding mallards. Journal of Wildlife Management 43:526-531. Fassett, N.C. 1957. A Manual of Aquatic Plants. University of Wisconsin Press, Madison, WI, USA. Grue, C.E., M.W. Tome, G.A. Swanson, S.M. Borthwick, and L.R.DeWeese. 1988. Agricultural chemicals and the quality of prairie-pothole wetlands for adult and juvenile waterfowl: what are the concerns? p. 55-64. In P.J. Stuber (Coord.) Proceedings National Symposium on Protection of Wetlands from Agricultural Impacts. U.S. Fish and Wildlife Service, Washington, DC, USA. Biological Report 88(16). Jarvis, R.L. and J.H. Noyes. 1986. Foods of canvasbacks and redheads in Nevada: paired males and ducklings. Journal of Wild. life Management 50: 199-203. Kantrnd, H.A., G.L. Krapu, and G.A. Swanson. 1989. Prairie basin wetlands of the Dakotas: a community profile. U.S. Fish and Wildlife Service, Washington, DC, USA. Biological Report 85(7.28). Krapu, G.L. 1974a. Feeding ecology of pintail hens during reproduction. The Auk 91: 278-290. Krapu, G.L. 1974b. Foods of breeding pinlails in North Dakota. Journal of Wildlife Management 38: 408--417. Krapu, G.L. 1979. Nutrition of female dabbling ducks during reproduction, p. 59-70. In T.A. Bookhout (ed.) Waterfowl and Wetlands--An Integrated Review. Proceedings of 1977 Symposium, Madison, WI, USA, Northcentral Section, The Wildlife Society. Krapu, G.L. and G.A. Swanson. 1975. Some nutritional aspects of reproduction in prairie nesting pintails. Journal of Wildlife Management 39: 156-162. LeSage, L. and A.D. Harrison. 1979. Improved traps and techniques for the study of emerging aquatic insects. Entomological News 90: 65-78. Mackay, R.J. 1984. Survival strategies ofinvertebrates in disturbed aquatic habitats. Journal of the Minnesota Academy of Sciences 50(3): 28-30. Merrill, R.W. and K.W. Cummins. 1984. An Introduction to the Aquatic Insects of North America. Second Edition. Kendall/Hunt Publishing Company, Dubuque, 1A, USA. Murkin, H.R. 1989. The basis for food chains in prairie wetlands. p 316-338. In A. van der Valk (ed.) Northern Prairie Wetlands. Iowa State Universily Press, Ames, IA, USA. Murkin, H.R. and B.D.J. Butt 1987. The interactions of vertebrates and invertebrates in peatlands and marshes, p. 15-30. In D.M. Ro~enberg and H.V, D~nks (ed~.) Aquatic Insects of Peatlands and Marshes. Memoirs Entomological Society of Canada 140. Murkin, H.R., P.G. Abbott, and J.A. Kadlec. 1983. A comparison of activity traps and sweep nets for sampling nektonic invertebrates in wetlands. Freshwater Invertebrate Biology 2:99-106.
Bataille & Baldassarre, MACROINVERTEBRATES FOLLOWING DROUGHT Murkin, H.R., J.A. Kadlec, and E.J. Murkin. 1991. Effects of prolonged flooding on nektonic invertebrates in small diked marshes. Canadian Journal of Fisheries and Aquatic Science 48: 2355-2364. Newson, H.D. 1984. Culicidae. p. 515-533. In R.W. Merritt and K.W. Cummins (eds.) An Introduction to the Aquatic insects of North America, Second Edition. Kendall/Hunt Publishing Company, Dubuque, IA, USA. Nudds, T.D. and J.N. Bowlby. 1984. Predator-prey size relationships in North American dabbling ducks. Canadian Journal of Zoology 62: 2002-2008. Pennak, R.W. 1978. Fresh-water Invertebrates ofthe United States, Second Edition. John Wiley & Sons, New York, NY, USA. Riley, T.Z. and T.A. Bookhout. t990. Response of aquatic macroinvcrtebrMes to early-spring drawdown in nodding smartweed marshes. Wetlands 10: 173-185. Ross, L.C.M. and H.R. Murkin. 1989. Invertebrates. p. 35-38. In E,J. Murkin and H.R. Murkin (eds.) Marsh Ecology Research Program Long-Term Monitoring Procedures Manual. Delta Waterfowl arid Wetlands Research Station Technical Bulletin 2. SAS institute, Inc. 1989. SAS/STAT user'sguide, version 6 Fourth Edition, Volume 2. Cary, NC, USA. SjSberg, K. and K. Danell. 1982. Feeding activity in relation to diel emergence of chironomids. Canadian Journal of Zoology 60: t383-1387. Smith, A.G., J.H. Stoudt, and J.B. Gollop. 1964. Prairie potholes and marshes, p. 39-50. In J.P. Linduska (ed.) Waterfowl Tomorrow. Bureau of Sport Fisheries and Wildlife, Washington, DC, USA. Stewart, K.E. and H.A. Kantrud. 1971. Classification of natural ponds and lakes in the glaciated prairie region. U.S. Fish and Wildlife Service Resource Publication 92Stewart, R.E. and H.A. Kantrud. 1973. Ecological distribution of breeding waterfowl populations in North Dakota. Journal of Wildlife Management 37: 39-50. Stoudt, J.H. 1982. Habitat use and productivity of canvasbacks in
269
Southwestern Manitoba, 1961-72. U.S. Fish and Wildlife Special Scientific Report Number 248. Sugden, L.G. 1973. Feeding ecology ofpintail, gadwall, American wigeon and lesser scaup ducklings. Canadian Wildlife Service Report 24. Swanson, G.A. and A.B. Sargeant. 1972. Observation of nighttime feeding behavior of ducks. Journal of Wildlife Management 36: 959-961. Swanson, G.A. and H.F. Duebbert. 1989. Wetland habitats of waterfowl in the prairie pothole region, p. 228-267. In A. van der Valk (ed.) Northern Prairie Wetlands. Iowa State University Press, Ames, IA, USA. Swanson, G.A. and M.I. Meyer. 1973. The role of invertebrates in the feeding ecology of Anatinae during the breeding season, p. 143-185. In The Waterfowl and Habitat Msnagement Symposium, Moncton, NB, Canada. Swanson, G.A, M.I. Meyer, and J.R. Serie. 1974. Feeding ecology of breeding blue-winged teals. Journal of Wildlife Management 38: 396--407. Wester, D.B. 1992. Viewpoint: replication, randomization, and statistics in range research. Journal of Range Management 45: 285-290. Wiggins, G.B., R.J. Mackay, and I.M. Smith. 1980. Evolutionary and ecological strategies of animals in annual temporary pools. Archive Hydrohiologie Supplement 58: 97-206. Wrubleski, D.A. 1987. Chironomidae (Diptera) of peatlands and marshes in Canada. p. 141-161, In D.M. Rosenberg and H.V. Danks (eds.) Aquatic Insects of Peatlands and Marshes-in Canada. Memoirs of the Entomological Sociew of Canada 140. Wrubleski, D.A. and D.M. Rosenberg. 1990. The Chironomidae (Diptera) of Bone Pile Pond, Delta Marsh, Manitoba, Canada. Wetlands 10: 243-275. Manuscript received 27 August 1992; revisions received 12 February 1993 and 23 June 1993; accepted 11 August 1993.