HOW DOES PREDATION FROM FISH INFLUENCE SPECIES AND
PHENOTYPE COMPOSITION AMONG BENTHIC INVERTEBRATE PREY IN
THE LITTORAL ZONE OF LAKES.
CHAPTER ONE
INTRODUCTION
Predation is attributed as a major selective force characterizing the structure of the
benthic invertebrate communities (Wellborn et, al. 1996). It has also been shown that
habitat differences and its gradients may influence such predation and the community
structure.
The community structures of freshwater shallow lakes include species of fish, numerous
invertebrates, amphibians, some reptiles and birds. Some invertebrates are known to be
associated with some types of the submerged vegetation and had evolved some
phenotypes expressions in terms of their sizes and pigmentation. Within the complex
domain of the aquatic plants or macrophytes, the predatory activities of the fish on
invertebrates is perceived to be limited (Gilinsky, 1984; Diehl 1992; Beckett et al., 1992);
thus providing a suitable niche for the invertebrates. Also outside the area covered by
macrophytes (in the open water),
the predatory fish will be more effective on the invertebrates’ prey, so a different pattern
of community structure may be expected (Tolonen et al., 2003).
Fish is considered a top predator in most permanent aquatic systems. They exhibit high
preference for large invertebrates ‘prey that swims actively; while invertebrates’ predator
may have preference for less active, small size preys (Wellborn et al., 1996). To this
ends, environment with high fish predation will in turn has greater abundances of small
size macro invertebrates, while on the other hand when invertebrate predation is
dominant, the small size invertebrates populations will be reduced, while there will be
growth in the size of the invertebrate predator populations (Nilson 1981; Crowder and
Cooper 1982; Bechara et al., 1993; Blumenshine et al., 2000).
Lampert and Sommer 1997 have indicated that small size macro invertebrates are more
vulnerable because of the fact that the predatory macro invertebrates cannot effectively
handle large size prey. In coastal wetlands, large size macro invertebrates were shown to
be dominant towards the shores, where fish predation is considered less significant
(Cardinale et al., 1998).
Many studies have been conducted in looking at the combine influences of fish and
invertebrates predator on the community structure of benthic macro invertebrates. Many
of such investigations usually happen in flowing water systems. Shallow lakes or ponds
provide suitable spots to investigate more closely how the two predation pressure can
affect the community structure of the aquatic macro invertebrates. A study of this nature
is useful in evaluating the impacts of human activities and eutrophication on the
biodiversity and community structure of an aquatic system in a basin. Lake
Eutrophication has strong impacts on fish status and the alternative stable states of the
lake systems. Human activities such as agriculture, aquaculture, fisheries, livestock
grazing, deforestation ,among others , have strong implications for the habitat quality
.Invertebrates benthic community in a lake system is highly regarded when defining the
status of the lake, in trying measure the impact of human activities ( Water Directive
2000/60/EC ; Solimini et al., 2006). Thus a research of this nature will be useful in
developing skills and knowledge in environment monitoring and evaluation
RESEARCH OBJECTIVES
1. To identify the fish species and the macro invertebrates present in the area
studied.
2. To find out the predator-prey relationship between the fish and the invertebrates,
by means of stomach analysis.
3. To find out the differences between macro invertebrates species compositions and
phenotype frequencies with respect to body size and pigmentation in the area with
submerged vegetation and area with emergent vegetation.
4. To relate the findings to the optimal foraging model of a predator- prey.
HYPOTHESIS
Ho There is no significant differences in macro invertebrates’ species compositions and
their frequencies in the two different habitats.
Ho There is no differences in the handling time for gammarus and other invertebrates
of same size.
DESCRIPTION OF STUDY SITE
Lake Takern is located in south of Sweden in Ostergotland provincial district
constituting Linkoping ,Norrkoping , Mjolby, Odeshog Motala and Vadstena as the
major urban settlement, close to the lake. It attracts numerous birds, thus very famous as
bird lakes. It spans across area of 12km long and 8km wide, with depth averaging
0.8metres. The lake and its contiguous area are nature reserve since 1975 and it is part of
Ramsar Convention list of protected nature. The site remains an enviable resource for
nature conservation, tourism and research. The nature reserve is managed by both
private ownership and State and about 5400 hectares is the size of the reserve area. 270
birds’ species had been found feeding and nesting in the area by birds’ watchers and
other visitors. Agriculture, livestock graze land and forest tree productions are the
common land use in the basin.
The lake habitat is structured by the type of vegetation present. At the reeds, there are
aquatic grasses dominating the landscape and with huge deposit of organic matter.
Further, there are clear water areas with sand and mud bottom, also area with submerged
vegetation distinctly,
Stonewort (Chara spp) and water milfoil (Myriophyllium spicatum). The Chara
dominated area has also clear water, as the Chara is seen some few centimeters under the
water, while the myriophyllium are seen up to the water surface.
This lake as noted earlier has got a strong reputation as a bird’s lake; it provides a
breeding ground for numerous visiting and residents birds in the north Europe. Ecological
studies of this lake have concentrated mostly on birds’ inventory and lately some interest
had been rekindled in the area of understanding the limnoligical past and future of the
lake. Not much has been known on the interaction between fish and invertebrates in the
two contrasting habitats defined by the presences of Chara and myriophyllium submerged
vegetation. It was the interest of this study to understand the predator prey relationship in
the lake
Google earth 2009
Figure 1. Map of Lake Tarkern
CHAPTER TWO
REVIEW OF LITERATURE
THE SHALLOW LAKE ECOSYSTEM
Shallow lakes refer to a body of permanent or semi-permanent water, which is
sufficiently shallow , less than 5 meters in depth ,that the light penetration extends to the
lake bottom and making primary production possible for the flora community (Wetzel,
2001). Valley et al. 2004 further classify shallow lakes based on the surface area it
covers and the alkalinity: small area <200hectares, large area >200 hectares and alkaline
>100ppm mg/L CaCO3, Not Alkaline <100ppm mg/L CaCO3.
Shallow lakes ecosystem is very productive, there are numerous aquatic plants due to
high nutrient availability and sunlight in the shallow lake. Emergent and floating plants
are common features, examples include: Cattails Typha spp, Bulrush, water lily
Nymphaea spp and reeds. There are also the submerged vegetation like the
myriophyllium spp, the Chara spp, and coontail. The vegetation provide habitat for the
zoo plankton, macro invertebrates, fish, birds and other wildlife (Conroy, 2005). There is
no vertical temperature stratification in shallow lakes. The water is consistently mixing
and the current is determined by the prevailing wind velocity. There is a high activity in
shallow lakes during summer period and in winter, the activity is low, and most benthic
organisms go into inactivity. Fish population in particular is reduced by occasional fish
kill due to low dissolved oxygen. The energy relationship in a shallow lake stems from
simple periphyton and phytoplankton, with sunlight energy for photosynthesis. There
are zooplankton and numerous invertebrates’ at different stages of their life cycle. There
are adult flying insects that intermittently visit the water. Fish have different feeding
behavior; some are planktivore, some benthivores and piscivores. Fish evolve different
feeding adaptation at different stage of development. A juvenile piscivore like perch
Perca fluviatilis L might feed on zooplankton and subsequently improve on its range of
prey choice , to include macro invertebrates of various kinds and in adult stage, its
choice will include cyprinids. Gammarus are intensely preyed upon by fish in most
freshwater system; this might be due to its food value and its vulnerable body nature, its
size and its activity (Wooster 1998, Mac Neil et al. 1999). Large size Gammarus are often
more vulnerable to fish predation as compare to smaller ones, same applicable to other
common prey. However, it is important to note that size of the predator determines its
capacity to handle its prey and thus a presenting a very strong factor on the choice of prey
and its size (Allan 1983, Allan and Malmqvist 1989, Andersen et al. 1993). Gammarus
spp is associated with detritus from leaf packs in Lake Bottom and also found closely
associated with periphyton in macrophytes rocks and also found to forage directly on
dead macrophytes (Newman 1991, Kornijow et al. 1995).
Fish predation on invertebrates: theories and applications
The interactions among organisms can be intra and inter specific. Intra specific is when
the interaction in within the same species either to enhance the species group efficiency
in the community or to promote individual dominance with a population towards resource
access. Inter specific interaction is one that demonstrates organisms of a population
having a feeding interaction with other different population; the later, describes the case
of fish predation on macro invertebrates.
To understand the phenomenon of predation, some theories had been advanced by
researchers to describe the processes that modulate predator and prey relations. One of
such theories is the optimal foraging concept (Emlen 1966; MacArthur and Pianka, 1966;
Charnov, 1976; Mittelbach 1981). It’s proposed that, in selecting prey size, predators
weigh the cost of handling a prey, to the benefits derivable in terms of energy gain from
the consumption of the prey; a predator will select prey size that will generate maximal
energy uptake per unit of handling time (Smallegange et al. 2008).
The adequacy of this theory was demonstrated in many studies involving molluscivores
predator for example crabs, selection of prey size that will maximize its energy gain
(Elner and Hughes, 1978; Hughes and Seed, 1995; Mistri, 2004). However, these
foragers on mollusc also express a flexible approach to prey selection, by feeding on
sizes that are less energy giving in order to reduce the cost or risk incurred during the
handling, or as a response to hunger, presence/absence of a competitor; this described
another theory which is called contingency theory (Hughes 1988; Visser 1995; Johnstone
and Norris, 2000; Rutten et al. 2006). Optimal foraging theory assumes an important tool
in studying feeding ecology because of its quantitative appeal in the prediction of
predator – prey relationship (Persson and Greenberg, 1990; Jackson and Rundle 2008).
Essentially, the optimal foraging model is to maximize E/t; where E, is the net energy
gain from the consumption of the predator, and t, the time taken for handling and
searching its prey; within the consideration, the cost also include the risk incurred in the
handling of the prey; so there is the question of the prey profitability, when different
preys are available to the predator at the same time.. Thus Jackson et al.2004; Jackson
and Rundle 2008, adapted the net energy optimal foraging model to describe the diet
shifts of goby (Pomatoschistus microps), when variety of prey were available. The
mathematical expressions of the predator- prey relationship were as follows:
Where E (J), t (s), λi rate of predation i (items s−1), A is assimilable part of energy, ei is
energetic content of prey i (J), Ch is handling cost (J s−1), Hi is handling time for preyi (s)
and Cs, the cost of searching (J s−1). A, assumed constant at 0·7, according to Elliott 1976
The results of the study demonstrated among others that an increase in prey size for goby
shows an increase in the handling time and also the predator size relate directly with the
size of the prey they consume (figure 1&2. Jackson and Rundle 2008).
Figure 2 Jackson and Rundle 2008.
The leading role of fish, in the structuring of the ecosystem in lakes and other aquatic
ecosystem, is very important in most aquatic ecosystem investigations. Much effort is
focus on this crucial role of fish as a leading predator as against other predators. Moss
(1976) observed an emergence increase in biomass of some kinds of macrophytes and
epiphytes, in artificially fertilized pond, which was stocked with bluegill sunfish. The
reason was that the fish population may have preyed on the invertebrates, which include
the community of amphipods and mayflies. Yellow Perch had been shown to have had a
very strong impact on the abundance of amphipods and chironomids and indeed leading
to an increase in the concentration of periphyton and particulate phosphorus; in the
absence of the fish population, the invertebrate were in abundance and thus decrease the
periphyton activities (Mazumdar et al. 1989). The feeding behavior of fish is also
modified by the factor of stage of its development, the size of its prey and also its natural
feeding niche. Thus there is the tendency for a fish to evolve its feeding from a simple
phytoplankton feeder, to zooplankton, larger invertebrates and becoming piscivores
(feeding in other fishes) at some point in time during its growth.
Schilling et al. 2009, investigated the phenomenon of fish absence in a lake as it affects
the macro invertebrates community structure , abundance , taxonomic constitutions and
the species richness. Their findings were that fishless and fish containing lakes have
many differences in the macro invertebrates’ structures and functions, thus fish absence
or presence pose a very strong factor that regulates the community structure and
functions. The introductions of fish in some lakes also have the tendency of declining of
native species of invertebrates and amphibians, due to fish predation. (Bradford et
al.1993; Denoel et, al. 2005).
Schilling et al. 2009 identified the abundance of six taxa that can serve as bio indicator of
fish absence in a lake, instead of undertaking a more rigorous task of fish sampling to
satisfy same purpose. In contrast, Wissinger et al.2006, proposed a modest effect of
introduced fish on invertebrates community, due to the presence of submerged
vegetation, the fish characteristics and the attributes of the prey. In fact, most
invertebrates were considered as habitat generalist as no local extinction was possible due
to fish predation. However, the threat of introduction of a top predator to the native
biodiversity cannot be disputed, due to evidence of decline in major native prey species
and cascading effects on ecosystem interactions and compositions following such
practice. (Townsend and Crowl , 1991; Larson et al. 1992; Flecker and Townsend ,1994
; Liss et al. 1995; Mack et al. 2000 Schindler and Leavitt, 2001; Nyström et al. 2003;
Simon and Townsend ,2003; Greig and McIntosh 2006; Dunham et al. 2006)
CHAPTER THREE
MATERIALS AND METHODS
Different approaches had been used by researchers in a bide to understand the complex
nature of interaction in an ecoligical community. Some seems to narrow investigation to a
particular population ,while others may prefer a mix of population . In shallow lakes , the
use of cages or similar barriers to partition experimental block or units is well accepted(
Christer Bronmark 1994). However, such block or partitioning may occur in nature as
exemplified by the vegetative landscape of the studied area. Also, common is the use of
core samplying device to get the invertebrate community in the mud bottom in the
studied area. There is also the possibility of making experimental set up with plastic
bowl or aquaria and having different substrates bottom and introducing the predator
and the prey. I adapted my predator prey experiment in a laboratory set up using plastic
bowls and aquaria . Samplings were done in the field . Invertebrates were collected in the
field . Fish were collected from the local fisherman .
The approach to the study was a combination of both field sampling and laboratory
investigation of a predator fish and its prey. At Lake Takern, the benthic invertebrates
were sample with a sweep net and a sieve at the reeds and also in the area with
submerged vegetation . The samples were taken in plastics bucket, with a lid. In the
laboratory the benthic samples were sorted in a flat bowl containing clean water and the
invertebrates were picked into glass cylindrical tubes and preserved in ethanol. The
invertebrates were then identified into their various families with the aid of a microscope
and an invertebrate manual. Measurement were made in (mm) with the aid of square
papper mark placed under a petri disc and observed through the microscope.
Fish sampling was conducted in Lake Takern using gill net. The gill nets were deployed
overnight, both in the reeds and in the area with submerged macrophytes. The fish were
removed from the gill net, sorted, and the standard length and weight were measured.
Samples of the fish tissues were taken and subsamples of the fish were taken for gut
content examination. Pair of surgical blade and scissors were used for this purpose; the
gut content were in turn introduced to petri disc and then view with the microscope to
identify invertebrates parts remains, in the gut.. Fish sampling were done at both northern
and southern landscape of the lake.
To investigate the benthic invertebrates structures and compostion is very vital in
understanding the food chain and the intractions that is possible within an ecosystem.
Thus samples of the benthic invertebrates were taken at two different contrasting habitats
in the lake landscape. It was also imperative to know the type of fish composition in the
lake and also the frequency of their distribution in the two habitat type. Thus fish
sampling was carried out, inorder to know what perhalps is the predator and the
herbivores fish species in the lake environment.
EXPERIMENTAL DESIGN
In the laboratory, perch predations on Gammarus spp and Corixidae (water boatman)
were investigated using 100mm- 105mm size of perch. Two size groups each of
Gammarus spp and Corixidae were fed to the fish at different feeding occasions in an
aquarium and two plastic fish holding bowls fitted with aerators and filters. The
aquarium was partioned with vertical slide glass attached to a string which manually
released to enhance drop down to partioned fish and prey or pulled to removed the
barrier ,thus creating fish and prey access. There was also a paper screen to minimize
human interaction on the fish activity in the aquarium.
The searching time and handling time were estimated in each feeding time using a stop
watch and the number of prey taken by the fish per time were measure (the attack rate).
Aselus was equally used as the third prey organism and the handling time were observed
. In all, there were three different prey organisms and only one predator fish species
replicates each. Ten individual prey were introduced to the aquarium stocked with Perch
in a group of three individuals at a time and one individual was observed and the
handling time taken. The proceedure was repeated 7 times in a day using different fish
individual, and for three days, each day taken as a replicate. 21 individual fish were used
the average handling time was taken. Fish that were observed to be less active were
replaced by the active individuals that were on a standby. The fish were stocked three in
an aquarium because of their known social behaviour which promote activities
In the experiment with Corixidae and Gammaru ,handling time was estimate for the
prey size category and three different fish individual was represented across the size
category of the prey and replicate were made for three days.
DATA AND DATA ANALYSIS
Primary data were obtained both from the field sampling and exprimental set up. Data
from the field include fish lenght and weight relationship, the benthic invertebrates
distribution, fish gut content , among others. In the experimental set up, data on Perch
handling time for three different invertebrate category were obtained. Some of the data
were analysed using Excel. The mean, standard deviation and the covariance of the
samples were calculated.
30
25
20
Hta
15
Htb
10
Htc
5
0
1
2
3
Figure 4. Perch predation on Corixidae, ( hta. 6-7mm, htb.8-9mm, htc 10mm) for days 1,
2 and 3, and the y axis shows the mean of the handling time.
30
25
20
hta
15
htb
htc
10
5
0
1
2
3
Figure 5. Perch predation on Gammarus pulex,
( hta 6- 7mm, htb. 8-9mm, htc 10-11mm) for days 1, 2 and 3.
9
8
7
6
5
4
3
2
1
0
1
2
3
Figure 6 .Perch predation on Aselus of size 6-7mm.
The pattern found in the Perch predation on Aselus shows a tendency towards an
increasing learning and experience of the fish; from day one to the third day, see a
reduction in the prey handling time of the fish. Day 1 and 2 were above 6 seconds per
prey while in day 3 it was less than 6 seconds.
CHAPTER FOUR
RESULTS AND DISCUSSION
4.1. FISH SAMPLES
The samples of the fish taken from the gill net were mainly Roach (Rutilus rutilus),
Perch ( Perca fluviatilis), Tench (Tinca tinca), and Rudd ( Scardinius erythrophthalmus)
The sampled populations are given in the following summary table and with a chart.
Table 1 category of fish caught by gill net.
roach
perch
Tench
Rudd
chara
83
5
2
6
reeds
273
56
0
0
3 individuals Perch were collected from the reed, the rest of the Perch were got from the
Chara habitat and their sizes ranges between 55mm and 180mm. Also in the Chara
habitat, 2 Tench of 400mm in lenght and 6 Tudd of between 160mm to 240mm were
found (figure 7 below
1
0.9
0.8
0.7
0.6
0.5
chara
0.4
reeds
0.3
0.2
0.1
0
roach
perch
Tench
Rudd
Figure 7. The proportion of fish sampled with gill net at Lake Tarkern
4.2.
THE BENTHIC INVERTEBRATES SAMPLES AND THE FISH GUT CONTENT
Benthic invertebrates’ samples were taken at random sweep using a hand net, in Lake
Tarkern. The about 16 families of the invertebrates were identified from the samples,
which include. The details are as follows, in figure 8.
Liplus sp
Physa sp
Ixodidae
Planorbis
Lymnea stagnalis
Bithynia
Lymnea poregra
Limnephilidae
Hirudinea
Zygoptera larvae
Polycentropodidae
Chironomidae
Corixidae
Asellus aquaticus
reeds
chara
0
0.1
0.2
0.3
0.4
Figure 8. The benthic invertebrate sampled in Lake Tarkern. There was more
invertebrates representation in the Reeds than in the Chara . The reason could be as result
of increasing complexity of the reeds vegetation of the lake, than the chara dominated
area.
Also, in the fish gut, four different invertebrates were found to be eaten by the perch, and
were at some stage of digestion, thus the body parts such as the head, abdominal segment,
wings and limbs of the invertebrate were examined and counted.
120
100
80
60
gut
expected
40
20
0
Asellus
Corixidae
Chironomidae
Zygoptera
larvae
Figure 9. Bar chart showing the invertebrates found in the gut of Perch, the fish caught by the gill
net. The expected numbers were estimated using Chi square statistics. A Chi square statistics
was used to test the significant of the samples found in the fish gut The critical value of
the chi square was 7.815, at degree of freedom 3 that is (n-1), n , number of different
category and at 0.05 error level, thus the results indicate a significant difference between
these distributions( figure 9 ).
4.3.
FISH PREDATION EXPERIMENT
The results of the predation experiment using Perch of 100mm in size and invertebrates
prey of (6- 8mm, hta ) size were compared for the same size of prey across the three
prey category and are shown in the following figure.
9
8
7
6
5
asellus
4
Corixidae
3
Gammarus
2
1
0
1
2
3
Figure 10. The Mean and SD of perch handling time for Asellus, Corixidae and
Gammarus.
hta
Days
1
Mean
Asellus
6.38
Corixidae
6.574
Gammarus 6.068
2
3
1
SD
2
3
6.513
5.945
6.25
5.541
7.443
6.9
1.637 1.469 1.579
0.488 0.575 0.154
0.398 0.556 1.35
Perch predation on Asellus aquaticus showed a pattern of reduced handling time from the
mean of 6.4, and 6.5 seconds for day 1 and 2 to 5.5 seconds in day 3. For Corixidae it
was 6.5 seconds, then 6 and 7.4 seconds the third day demonstrating increasing constraint
to predation. Gammarus was from 6 seconds, 6.2 and 7 seconds the third day, also,
demonstrating an increasing constraint to predation. Differences in pattern of handling
can be attributed to factors such as the willingness of the predator itself to respond to the
prey availability, familiarity of the predator with the prey, and also the predator response
to the observation environment. Part of the procedure was to get the predator use to the
prey items a day prior to the experiment as they were being fed on the prey items. The
water quality was equally monitored to minimize water quality stress factor. Prior to the
experiment with the Asellus aquaticus, there was water quality problem and the fish were
off feed, the water was then replaced and leftover food items in the water were removed,
this could have posed a potential biochemical oxygen demand.
DISCUSSION
SAMPLING TYPES AND WHY?
In the investigation of the research questions sampling were carried out in the field and in
the experimental set up. Fish sampling was done in order to have an insight of the type
of fish present in the lake that could be prominent a benthic invertebrate predator. The
gut content of the fish that were caught was also examined and data of the gut gives an
enhancing indication of the variety of prey organisms available and eaten by the fish. In
the fish sampling the Roach were more in number but their gut content analysis revealed
so little of their prey organism, but as for the Perch it was possible to identify different
prey organism, both in parts or appendages and in whole. Thus using Perch as the benthic
predator in the predator and prey experiment was an adequate choice.
Also, hand net samples of benthic invertebrates samples were taken at both reeds and
chara macrophytes vegetation area of the lake. However, there were no differences in the
benthic invertebrate’s samples distribution; there was the general habitat complexity in
the two areas. Evidently, preyed organisms found in the fish gut relates to the hand net
samples of the benthic invertebrates. This procedure is of many ways to understand the
interactions between organisms in a community.
FISH PREDATION ON INVERTEBRATES
The invertebrates’ distribution in an aquatic environment is a noted factor that affects the
fish carrying capacity (Wetzel 2001). The fish depends on a wide variety of invertebrates’
prey existing at different stages of life cycle. Fish has been described as the dominate
habitat regulator, a top predator in an aquatic system. (Vanni 1986, Hansen and
Jeppesen, 1992, Scheffer 1998). The presence or absence of some species of
invertebrates in a lake is used as an indicator of fish or fishless lakes in some recent work.
In some habitat regulation or management, it is not uncommon to have fish introduction
to water that was in hitherto fishless or with less fish, either to satisfy habitat need or a
sustainable resources. It is vital to study the fish predation and the interactions with other
members of the community.
In the fish predation experiment Perch predation on Asellus aquaticus, Gammarus pulex,
and Corixidae were observed. There was evidence of the Perch catching, chewing and
swallowing the prey organism. It was equally important to observe the role of social
group behavior of the predator. A single predator in an aquarium is but redundant and
uninterested, that is different when they are in threes.
Handling time was used as means of estimating further the biomass intake of the prey
item. Handling time defines the time taken between one action of attacking the prey and
the commencement of another attack. To be effective, some handling time may be longer
due to an incorporating search time in between actions. Handling time may also be due to
the prey size or familiarity to the predator. The nature of the body of the prey may also
affect the handling time. Prey with soft body are likely to be taken easily that those with
rough body appendages. These and other factors may simultaneously affect the fish
handling time of the invertebrates. In the experiment a progressive time reduction of
handling time for Asellus aquaticus was observed, this could have been as a result of
learning and experience with the prey item. However, for Gammarus pulex and Corixidae
such progress was not prominent.
.
RESULTS AND THE RESEARCH QUESTION
The research questions constructed from the hypotheses’ include:
Are there any significant difference in the macro invertebrate species composition and
their frequency in the two habitats? Secondly, are there any differences in the handling
time for Gammarus pulex and other invertebrates of same size? Statistical evaluation of
these two questions from figure 8 and 10 respectively. Using one way ANOVA.
SUMMARY AND CONCLUSION
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Appendix
Corixidae
Day
1
2
mean
sd
Covariance.
6.574
0.488
7.417
9.9
0.381
3.849
22.08
2.04
9.241
3
5.945
0.575
9.677
9.847
0.375
3.813
15.02
2.665
17.75
7.443
0.154
2.07
7.353
0.853
11.6
11.43
0.634
5.546
Gammarus
Day
mean
sd
Covariane
Aselus
1
6.068
0.39
6.56
6.613
1.52
23.0
17.6
3.666
20.8
2
6.25
0.55
8.89
5.493
0.625
11.3
16.8
2.078
12.3
3
16.8
2.078
12.37
6.995
1.351
19.31
Day
1
2
3
Mean
6.38
6.513
5.541
Sd
1.637
1.469
1.579
Cov(%)
25
22.56
28.5
n
21
6.767
1.383
20.44
22.02
2.659
12.07