acta oecologica 32 (2007) 59–66
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Original article
Primary succession of Acrididae (Orthoptera): Differences
in displacement capacities in early and late colonizers
of new habitats
F. Picauda, D.P. Petitb,*
a
Société Entomologique du Limousin, Avenue Baudin, 87000 Limoges, France
INRA UMR 1061, Limoges, Université de Limoges, 123 Avenue A. Thomas, F-87060 Limoges Cedex, France
b
article info
abstract
Article history:
Rehabilitated mine sites are suitable environments for the study of primary ecological
Received 25 May 2006
succession. Following the monitoring of Plant and Orthoptera communities for 4 years on
Accepted 12 March 2007
7 sites in the Limousin region (France), covering 9 years of rehabilitation, three grasshopper
Published online 25 April 2007
seres were defined. It is expected that these seres are conditioned by both displacement
capacities and reproductive characteristics. This study compares by field experiments the
Keywords:
jumping flights and walking speed of the most abundant Caelifera belonging to the defined
Primary ecological succession
seres. A strong link emerged between the successional stages, the distances covered by
Orthoptera
jumping flights and sexual dimorphism. Walking speed is poorly related to the successional
Dispersal capacity
stage. We show that the high density of some species, as observed in the medium stage of
Sexual dimorphism
succession, significantly reduces the walking distance of late colonisers, suggesting a mechanism that reduces further colonisation.
ª 2007 Elsevier Masson SAS. All rights reserved.
1.
Introduction
When an area that has been cleared of vegetation is allowed to
revegetate, the primary succession that follows is characterized by an initial increase in the number of species during
the first few years, followed by a slight decrease as has been
shown for ants, reptiles and birds (Blondel, 1976, 1979; Brown
and Southwood, 1987; Majer, 1989). In the case of ants living in
sand quarries in Queensland, Australia, Majer (1989) reported
that the highest number of species was observed 6 years after
site rehabilitation. In their colonization study of four islands
off Florida, Simberloff and Wilson (1969) showed that the
greatest number of Arthropod species (having a high dispersal
capacity) was observed at around 180 days. Hawkins and
Cross (1982) showed a decreasing number of Arthropod
species from the first year on (Araneae and more than 10
insect Orders) in zero to 5-year-old coal mine spoils.
The underlying explanation of this pattern can be divided
in 2 parts. In the early stages, there is a progressive gain of
colonising species over time, but it is not clear why there is
then a plateau or even a decline in the number of species.
Lack (1976) in Blondel (1979) has hypothesized that several
species belonging to medium or late seres inhibit the settlement of other species.
The process by which there is an increasing number of species during the early stages of succession is not likely to result
from a random arrival of species. The first species to settle in
the new area are likely to be those present in nearby ecosystems and further depends on properties of species themselves, including dispersal ability and reproductive rate. In
* Corresponding author. Tel.: þ33 5 5545 7382; fax: þ33 5 5545 7201.
E-mail addresses: [email protected] (F. Picaud), [email protected] (D.P. Petit).
1146-609X/$ – see front matter ª 2007 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.actao.2007.03.005
60
acta oecologica 32 (2007) 59–66
the case of terrestrial environments, vegetal composition and
cover varies during the course of succession, and the availability of trophic resources and existence of refuge zones select
the candidate species to colonise the new area. As for insects,
several authors (Southwood et al., 1979; Brown, 1982a,b;
Simberloff and Wilson, 1969; Majer, 1989) have pointed out
the characteristics common to the species belonging to different seres within a succession: (i) the pioneer species have
a high potential to disperse, a high fecundity, a resistance to
variable conditions; and (ii) late species are advantaged in
competition due to a greater size of their body and of their
offspring.
In previous work (Picaud, 1998; Picaud and Petit, 2007),
we have studied a primary ecological succession of Orthoptera
in post mining areas in the Limousin region (France), taking
advantage of the availability of diachronic and synchronic
investigations (Andersen, 1997; Majer, 1989). Orthopteran
communities were monitored for four years on seven mine
sites in Haute-Vienne (France), covering a 9-year sequence.
We showed a peak of richness between 2.5 and 3.5 years of
rehabilitation age, and found that this richness was negatively
linked to the height of herbaceous vegetation. Three seral
stages of Caelifera were described and assigned to pioneer,
medium and late species communities. Against, Katytids (Tettigonoidea) succession appeared to be more linked to vegetation structure variations than to the elapsed time from the
starting point of colonisation. The distances moved by the insects from the surrounding areas (road edges and ditches, cut
grasslands and humid zones) toward the mine sites were limited in reason of their weak surfaces (0.8–16.5 ha). Interestingly, the fauna of pioneer to medium seral stages looked
like the one observed in road edges and ditches (more or
less disturbed habitats), whereas the one of older stages
were close to cut grasslands (more stable habitats). Given
the topology of the sites, it was likely that colonisation process
occur through road edges and ditches. As all the insects seen
on these environments were eating or walking, and jumping
away at our approach, walking was the first hypothesis concerning the way they could reach mine sites.
The aim of this work is to determine if displacement capacity
of the most abundant species of Caelifera is related first to colonisation order during succession and secondly to the diversity
decline observed from the 4th year. We tested the hypothesis
that colonisation is related to long-distance dispersal (see
Nathan, 2005 for review) and/or to diffusion, and we have studied the two possible modes enabling these insects to move: occasional jumping flights and walking (Andow et al., 1990; Bailey
et al., 2003). It is possible that colonisation process varies according to the species, i.e., long-distance dispersal for good flyers,
probable for sere 1 species given the relative length of their
wings, and diffusion for bad ones, e.g., flightless species, a frequent trait in sere 3 species (see studied species in Section 2).
Due to numerous environmental factors, such as topography, prevailing wind direction, zenith orientation (Narisu and
Schell, 2000) and habitat preference of the different species
(Hein et al., 2005), it may become difficult to interpret the characteristics of dispersal of grasshoppers in field conditions
(Gardiner and Hill, 2004). Although the occurrence of jumping
flights is certainly rare in field conditions relatively to walking,
the mark-recapture experiments from one day to the next one
cannot separate these two aspects of movement. Moreover, the
risk of individual lost observed in mark and re-sight studies in
open fields often ranges from 30 to 50%, even with reflective
tapes and night observations (Hein et al., 2005). So we undertook experiments to compare the walking performances of different Caelifera species under the protection of a tent and the
jumping flights in semi-controlled conditions. More precisely,
we undertook walking measures with two conditions of grass
height, for two reasons. First, we showed (Picaud and Petit,
2007) that the vegetation height of herbaceous environments
varies during the course of succession: around 35 cm in 0–
2 years old sites, 12 cm in 2.5–3.5 years old sites and 25 cm in
sites older than 4.5 years. Secondly, Hein et al. (2005) have demonstrated that a grasshopper walks faster in an unsuitable habitat (tall grass for example) than in preferred one (short grass).
The results of both displacement modes of each species were
compared to the order in which they appeared on post mining
areas. Given the particular role of female in the settlement of
successive generations, we tested if there is a sexual dimorphism affecting the dispersal performances during jumping
flights and walking. Finally, we tested if diffusion by walking
varies according to the abundance of a previously settled species. If the response is positive, we could address one of the crucial steps explaining the decreasing diversity often observed in
late stages of succession.
2.
Materials and methods
2.1.
Studied species
Following our previous work dealing with post mining areas,
(Picaud and Petit, 2007), we define the composition of the
3 seres of Caelifera:
Sere 1: Aiolopus thalassinus (F.), Chorthippus brunneus (Thunberg), Oedipoda caerulescens (L.) and Calliptamus italicus (L.),
Sere 2: Chorthippus biguttulus (L.), Omocestus rufipes (Zetterstedt), Stethophyma grossum (L.), and Stenobothrus stigmaticus
(Rambur),
Sere 2 or 3: Chorthippus albomarginatus (De Geer) possibly
assigned to sere 2 but may be in sere 3.
Sere 3: Chorthippus dorsatus (Zetterstedt), Chorthippus montanus
(Charpentier), Chorthippus parallelus (Zetterstedt), Euchorthippus declivus (Brisout), and Chrysochraon dispar (Germar). Because of its low abundance, this last species was not studied
in our previous work. The females have vestigial hind wings
in C. montanus, C. parallelus and C. dispar, and reduced ones
in E. declivus.
2.2.
Measures of jumping-flights
For each Caelifera species (O. caerulescens, A. thalassinus,
C. brunneus, C. biguttulus, C. parallelus, C. albomarginatus,
O. rufipes, E. declivus and C. dispar), 10–20 adult females and
10–20 adult males were studied (3689 measures, see Table 1).
To standardize performances for the jumping flights, we applied a series of 4 stimuli to each individual, in a given order:
(i) presence of experimenter at 1 m-distance from the insect;
61
acta oecologica 32 (2007) 59–66
Table 1 – Jumping flight capacities (in m, neperian log-transformed values) of males and females of grasshoppers common
in the different stages of succession. The measurements were made on 10–20 males and 10–20 females for each species
Succession stage
Species
Sere 1
A. thalassinus
C. brunneus
O. caerulescens
Sere 2
Male: mean SEM
Female: mean SEM
N
ANOVA
2.058 0.238
0.944 0.040
0.440 0.117
1.362 0.089
0.432 0.088
0.643 0.117
142
166
182
F1,140 ¼ 8.81, P ¼ 0.004
F1,164 ¼ 8.15, P ¼ 0.005
F1,180 ¼ 1.51, P ¼ 0.22 NS
C. biguttulus
O. rufipes
0.535 0.04
0.254 0.058
0.281 0.037
0.358 0.038
425
474
F1,423 ¼ 17.47, P < 0.001
F1,472 ¼ 2.93, P ¼ 0.088 NS
Sere 2–3
C. albomarginatus
1.243 0.037
1.2215 0.037
524
F1,522 ¼ 0.27, P ¼ 0.60 NS
Sere 3
E. declivus
C. parallelusa
C. dispara
1.093 0.034
1.092 0.032
0.455 0.014
1.246 0.030
1.311 0.041b
0.541 0.016b
639
547
590
F1,637 ¼ 11.40, P ¼ 0.001
F1,545 ¼ 17.05, P < 0.001
F1,588 ¼ 16.45, P < 0.001
a Hind wings strongly reduced.
b Tegmina short and hind wings absent.
(ii) approaching the insect inside a 1 m-radius circle; (iii) simulated capture with the hand; and (iv) touching the insect with
the fingers. During each series of experiments, the first stimulus was applied until the insect’s response began to decrease,
then the following stimulus was applied, and so on. Each measure was recorded on a recently mowed lawn at La Borie University Campus, Limoges, on windless days at temperatures
between 20 C and 25 C. Data were log-transformed to maintain normal distribution and to perform multi-way ANOVAs.
Pair-wise comparisons were made with Tukey’s test.
2.3.
Measures of walking
Point zero
1.7 m
The most common Acrididae species in Limoges region were
collected so as to get at least 50 individuals by species: 2 species belong to Oedipodinae (O. caerulescens and S. grossum) and 7
to Gomphocerinae (C. brunneus, C. biguttulus, O. rufipes, C. dorsatus, C. albomarginatus, C. parallelus and E. declivus). In all, 787 individuals were tested. Due to an insufficient number of
collected specimens, experiments dealing with C. dorsatus
and S. grossum were limited to tall grass.
A preliminary field experiment was conducted on a flat
topography and homogeneous herbaceous vegetation with
a mean height of about 25 cm, in Puy-Teigneux mine site
(Bessines-sur-Gartempe) in July 1996. Male and female individuals of C. dorsatus were captured on the site, marked on
the pronotum with nail varnish and released near a wood
peg. We resighted only about 1/3 of marked specimens 24 h
later, due to predation and escape. Results revealed an eastwest preferential displacement orientation and a limited distance covered of less than 5 m.
Three tents were built on a flat surface of prairie (Poaceae
representing 90% of total biomass) belonging to the Conservatoire des Espaces Naturels du Limousin, at the Theil (SaintGence, Haute-Vienne, France). Each tent was east-west
oriented with the following dimensions (L l H ¼ 1.5 20 1.70 m, Fig. 1). In order to limit temperature variations
while enabling humidity and light transfer, over each tent
was placed an armature of 22 two metre long wooden sticks
regularly driven into the ground and covered with a growing
net. The centre point, where grasshoppers were released,
was marked with a small vertical stick. Prior to each
experiment, native insects and spiders were removed, ensuring that almost released grasshoppers were recaptured and
that the only disturbances were limited to those caused by
the experimenter. As a result, jumping flights were unlikely
to occur.
Experiments were conducted simultaneously with 3 tents
in order to obtain results under the same conditions in a short
period of time. During September and October 1996, we estimated the regularity of displacement from one day to the
next one with capture-recapture experiments. We also measured the effect of temperature with observations made at
18 C and at 32 C. During July and August 1997, the temperature was recorded for all the duration of experiments (Fig. 2).
The weather was sunny and rather constant and most results
were acquired during this last period.
Two to three series of experiments were undertaken for
each species and each sex with both grass heights: a first series
with an average of 45 cm 5 cm-height grass (‘‘tall grass’’), and
a second series with 5 cm 2 cm-height grass (‘‘short grass’’).
Each experiment series began with a new set of more than 30
individuals. Each measure consisted in recording the distance
and the zenith orientation between the point zero and each individual 24 h after release. The position of each individual was
then projected onto an east-west axis (Fig. 3a,b).
As walking is the main dispersal mode of species belonging to
sere 3 in reason of reduced hind wings of females, we tested if
their speed were influenced by the presence of medium sere species. We chose two species among the most abundant ones of
sere 2 and 3, i.e. C. biguttulus and C. parallelus respectively. The
measurements of C. parallelus displacement were performed in
the presence of 4 different densities of C. biguttulus (0, 1, 2 or 3
individuals homogeneously placed per m2), and on short grass
1.5 m
20 m
Fig. 1 – Tent. Insects are released at point zero for walking
experiments.
Temperature °C
62
acta oecologica 32 (2007) 59–66
50
45
40
35
30
25
20
15
10
5
0
0
2
4
6
8
10
12
14
16
18
20
22
Universal time
Fig. 2 – Daily temperature variations (mean ± SEM) between
the 6th and 16th of August.
because insect community parameters of old herbaceous environments of mine sites were found to be close to those of cut
grasslands in surrounding areas (Picaud and Petit, 2007).
Each data set corresponding to a species, a tent and a day
was used to calculate mean and variance. The normality of
the data was assessed with the Kolmogorov–Smirnov test.
The mean corresponds to the drift of the population and for
each pair of species, ANOVA tests were used to compare relative drift. The variance relates to diffusion which was tested
using a Fisher test. Both tests used N 1 as degrees of
freedom.
In order to estimate the distance moved by walking during
one generation, we retained a mean life-time of 20 days, although it probably depends on the sex (Bailey et al., 2003). We
simulated with DISP program the maximum activity radius
(RMAX), i.e., the greatest distance between the first observation
point and any observation point (Samietz and Berger, 1997) and
this was calculated for 100 replicates. For each simulated day,
the individual distance results from a number taken at random
within a normal series, taking into account the standard deviation of daily measured distance; the orientation is given by
a random number taken between 0 and 360 . The program
DISP functions under MS-DOS and is available on request.
All the statistical analyses (Kolmogorov–Smirnov tests,
Pearson correlations, Spearman ranks correlation, Kruskal–
Wallis tests and ANOVAs) were conducted with SYSTAT
vers. 7.0 (SPSS Inc., 1997).
A
S
W
E
N
B
S
W
E
N
Fig. 3 – Diagram of insect position recorded in the tent.
Cross: male, dot: female. a. Observed positions: x and y
coordinates recorded. S: South, E: East, W: West, N: North.
b. Projection of points on x axis.
3.
Results
3.1.
Jumping flight in herbaceous zones
We tested if the different seres of adult Caelifera, based on the
results of our previous work, differed by their jumping flights.
We recorded 1895 distances for males and 1784 for females,
corresponding to 9 Caelifera species.
The distances covered during jumping flights by species in
sere 1 were significantly (P < 0.001, Tukey’s test) longer than
those of sere 2, which in turn, were longer than those of sere 3
(Fig. 4A,B). C. albomarginatus covered distances close to those
of the latter group. The mean distance covered jumping
flight ranged from about 8 m (male of A. thalassinus ln 2.058;
Table 1) to about 0.27 m (female C. parallelus ln 1.311, Table 1).
Among the studied species, three showed no sexual differences for jumping capacities: O. caerulescens, C. albomarginatus and O. rufipes (Table 1). When sexual differences were
recorded, the males jumped farther except for C. biguttulus
(F1,423 ¼ 17.47, P < 0.001). There was no dimorphic tendency
in the species of seres 1. The males of all the species of sere 3
(C. parallelus, E. declivus and C. dispar) jumped significantly farther than females (P 0.001).
The sensitivity of individuals toward the applied stimuli
varied according sex and seres (Fig. 5A,B). Females reacted
less than males (Kruskal–Wallis, P < 0.0001); moreover, species belonging to sere 3 showed a weaker sensitivity
(Kruskal–Wallis, P < 0.0001) than those of seres 1 and 2.
3.2.
Walking in tall and short grass environments
The temperature effect on dispersal on tall grass was tested
with C. albomarginatus (Table 2). Increasing temperature did
not significantly (P > 0.35, ANOVA test, N ¼ 72) effect the
mean distance moved (drift) but did effect the variance (diffusion) significantly (P < 0.05, Fisher test, N ¼ 72).
Reproducibility of individual dispersal was assessed by the
comparison of each marked insect during two experiments on
tall grass. Pearson coefficients of the projection of distances
within the five studied species (C. biguttulus, C. dorsatus,
C. albomarginatus, C. parallelus, and E. declivus) are reported in
Table 3. For individuals of all species tested, the distance covered was very variable from day to day (Pearson r, P > 0.30).
The result was that there were no especially fast or slow individuals within a species: an individual that was fast one day
was often slower on the next.
Variance ratios, corresponding to daily dispersal in high
grass vs. short grass for each species, are shown in Table 4.
C. brunneus and C. albomarginatus move at the same speed in
both grass heights. In contrast, two species walk significantly
faster in tall grass (O. caerulescens and C. parallelus), whereas
the C. biguttulus and E. declivus move significantly faster in short
grass. Variance ratios calculated for each species did not show
any significant difference between sexes. Calculations of
Spearman rank correlations, on the standard deviations of
daily walking between both grass heights, show that most often the species move in the same order (rho ¼ 0.886, P ¼ 2%).
The computed maximum activity radius of the different
species significantly differs between the seres (Fig. 6A,B).
63
acta oecologica 32 (2007) 59–66
A
B
2
3
1
Ocae
b
Atha
a
Cbru
b
Cbig
c
0
Oruf
c
-1
-2
Calb
d Edec
d
Cdis
d
Ln (jumps in m) ± SEM
Ln (Jumps) in m ± SEM
Atha
a
2
Cbru
c
1
0
Ocae
b
2
?
-1
-2
3
Calb
f
Cbig
d
Cpar
d
1
Oruf
e
1
Cpar
g
?
2
Seres
Cdis
d
Edec
g
3
Seres
Fig. 4 – Mean jumping flight (log-transformed measures, in m ± SEM) of different species of Caelifera. Different letters
correspond to significant differences (Tukey’s tests, P < 0.001). A: females. B: males. Atha: Aiolopus thalassinus; Ocae:
Oedipoda caerulescens; Cbru: Chorthippus brunneus; Cbig: C. biguttulus; Oruf: Omocestus rufipes; Calb: C. albomarginatus; Edec:
Euchorthippus declivus; Cpar: C. parallelus; Cdis: Chrysochraon dispar.
Both species of sere 1 (O. caerulescens and C. brunneus) move
significantly longer distances than the species of seres 2 and
3, whatever the grass height (Tukey test, P < 0.001). The species of sere 2 move less or equally to the species of sere 3,
whatever the grass height. C. albomarginatus displacement is
in the range of the species of seres 2 and 3.
Otherwise, the conducted ANOVAs on drift values show
that: (i) in short grass, neither species (6 species and 347 individuals), nor sex and the combination of both factors have a significant effect on drift; and (ii) in tall grass, drift varies
significantly according to species (8 species, 504 individuals,
P ¼ 0.1%) but not to sex and sex*species combination. Comparison of drift means obtained in tall and short grass did not
reveal a significant rank correlation (Spearman rho ¼ 0.086,
P > 5%).
Influence of an already settled species on walking
The presence of low densities of C. biguttulus (sere 2) had no
effect on C. parallelus (sere 3) dispersal, estimated by diffusion
Stimulation type
A
a
b
1
0
m
f
Sex
Discussion
4.1.
Relationship between colonisation order
and modes of displacement
The position of each Caelifera species during succession can
be related to different dispersal capacities. Interestingly, the
three Caelifera seres defined from field samples correspond
to clear cut jumping-flight performance groups. Two criteria
can be proposed to enabling long-distance dispersal: (i) relatively good flyers in both sexes, as observed in the 3 species
of sere 1; or (ii) better performances of females over male
ones, as observed in C. biguttulus (sere 2). Obviously, the limit
between ‘‘good’’ and ‘‘medium’’ flyers is arbitrary. Our finding
corroborates the model of Hovestadt et al. (2000) who showed
B
3
2
4.
Stimulation type
3.3.
(Table 5). But when the density of C. biguttulus was equal to or
greater than that of C. parallelus, there was an increasing
reduction in C. parallelus dispersal on short grass (Table 5).
3
b
2
a
a
1
0
1
2
3
Seres
Fig. 5 – Stimulation types (mean ± SEM) applied to Caelifera species, according to sex (A) and seres (B). The different letters
correspond to significant differences (P < 0.0001) with Kruskal–Wallis tests. f: females; m: males.
64
acta oecologica 32 (2007) 59–66
Table 2 – Temperature effect on the dispersal of
C. albomarginatus on tall grass. N.S.: non-significant;
*: P < 0.05
Table 4 – Fr values (intraspecific comparisons of
variances) between tall and short grass. z: marginally
significant; *: P < 5%, ***: P < 0.1%
T C N Mean Drift: ANOVA Variance Diffusion: Fisher’s
test
Species
18
32
Oedipoda caerulescens
36 119.39
36 54.14
P ¼ 0.373 N.S.
61,543.1
129,117.1
2.10*
that the patterns observed in plant succession can be simulated by simply varying the dispersal distances of species. In
contrast, differences in walking, as measured by the diffusion
process, are not related to the sere order of succession. The
drift observed during walking is variable and weak in extent
and is unlikely to play any role in the colonisation of a new area.
4.2.
Relationship between biological traits
and modes of displacement
Even though walking probably contributes little to dispersal,
the pioneer species of sere 1 cover the largest distances in
both jumping flight and walking. We interpret this observation
by the probable requirement of strong thoracic muscles to
move the tegmina and wings, which are in these species longer
than in the Acrididae belonging to the following seres (Picaud,
1998). More generally, Simberloff and Wilson (1969) were able
to show that the pioneering insects (Dermaptera, Coleoptera
and Hemiptera) colonising islands were good long-flight species. Moreover, Brown (1982b; Brown and Southwood, 1983),
in their work on Heteroptera, Homoptera and Coleoptera, demonstrated that pioneer insects possessed longer wings.
In contrast, the latest species in the course of succession
(C. parallelus, E. declivus, and C. dispar) have the shortest flight
organs associated with the highest sexual dimorphism. Curiously, these species walk at the same speed or faster than the
ones of sere 2. Their short wings are somewhat balanced by
a better capacity to walk. This compensation has been
retrieved in flightless katytids, as Pholidoptera griseoaptera
(Diekötter et al., 2005).
4.3.
Stratified colonisation versus diffusion
Stratified colonisation assumes that the females can move by
two modes of dispersals, i.e., walking and occasional longdistance jumping flights. Long-distance dispersal is employed
here as the proportional distance defined in Nathan (2005),
Table 3 – Pearson coefficients of projection distances
between two experiments on tall grass (temperature
>30 C). N.S.: non-significant
Species
Chorthippus biguttulus
Chorthippus dorsatus
Chorthippus albomarginatus
Chorthippus parallelus
Euchorthippus declivus
r
0.148
0.101
0.033
0.192
0.236
N Threshold at the risk 5%
22
38
36
26
23
0.42
0.32
0.32
0.38
0.40
N.S.
N.S.
N.S.
N.S.
N.S.
Grass N Variance
height
Tall
Short
Chorthippus brunneus Tall
Short
Chorthippus biguttulus Tall
Short
Chorthippus
Tall
albomarginatus
Short
Chorthippus parallelus Tall
Short
Euchorthippus declivus Tall
Short
45
55
63
60
97
57
57
54
84
59
94
62
38.69
24.80
22.47
22.37
2.28
5.24
6.05
4.20
11.22
7.40
8.94
14.59
Fr
Probability
1.56 5.99% z
1.00 49.43% N.S.
2.30 0.02%***
1.44 9.16% N.S.
1.52 4.70%*
1.63 2.09%*
where a few individuals ‘‘reach distances that are longer
than those reached by most other dispersing individuals’’.
Once in their new location, they can lay down. It is difficult
to address directly the balance between the two modes of displacement in the case of grasshoppers. Our experiments bring
interesting elements since even if the jumping flights are occasional, they probably play a major role in the colonisation
process. Moreover, it is likely that the capacity to have sustained flights is strongly linked to the length of jumping
flights, obviously amplified by the wind. We can stress that
in the case of Acrididae, mobility adaptations are related to
the way the insects can escape predators. In open and young
sites, where vegetation is short, high mobility capacity is beneficial. In contrast, in older sites where vegetation cover and
height are more important, the insects can easily hide. Our experiments prove that the species of sere 3 are less prompt to
escape from a danger than the preceding ones.
The elegant use of random walking model has been successfully applied to C. brunneus and C. jacobsi in Spain by Bailey
et al. (2003). These authors evidenced a fat-tailed dispersal distribution, involving few events of jumping flights among the
displacement by walking.
In contrast, diffusion assumes that the dispersal results in
a progressive and continuous process. Walking and short
flights are involved in such mode of dispersal. Species in
sere 3, and perhaps C. albomarginatus, probably only move by
diffusion, since absolute values of walking variance are small,
and especially with females. Our results stress the importance
of the vegetation height in the maximum activity radius. It is
worth noting that C. biguttulus and E. declivus move significantly faster in short grass than in tall one in order to escape
unsuitable habitat. Similarly, O. caerulescens move faster in tall
grass, because the preferred habitats of adults are short grass,
as ever shown by Hein et al. (2005). However, in the case of
C. parallelus, this explanation does not hold because this species is not particularly frequent in short grass.
4.4.
Influence of previously settled species on walking
Several authors (Brown and Southwood, 1987; Majer, 1989)
have noted that the reason why diversity decreases in late
65
acta oecologica 32 (2007) 59–66
34.0
27.8
Ocae
a
21.6
Cbru
b
Edec
ce
Cbig
d
9.2
3.0
Calb
c
Sgros
ce
15.4
1
2
Cpar
e
Cdor
ce
?
3
RMAX over 20 days (meters)
RMAX over 20 days (meters)
34.0
27.8
Ocae
a
21.6
Cbru
a
15.4
Calb
c
Cbig
c
9.2
3.0
1
Seres
Edec
b
Cpar
c
2
?
3
Seres
Fig. 6 – Variations of RMAX (maximum activity radius) in a 20 days-period computed from the standard deviation of the
walking distance in 2 grass heights. A: tall grass, N [ 800; B: short grass, N [ 600. Different letters correspond to significant
differences (Tukey’s test), at P < 0.001.
stages of succession is poorly understood. Extrinsic and intrinsic causes have been evoked to explain this decrease. A
possible extrinsic cause is environmental factors unfavourable to the coexistence of Orthoptera species. In the case of
the reclaimed mines studied by Parmenter et al. (1991), the decreasing phase of Orthoptera diversity from the 2nd year on is
partly explained by parallel vegetation variations. Similarly,
our previous study on mine sites showed that there is a significant negative correlation between species richness and grass
height in herbaceous environments during the 9 years course
of succession. Moreover, the development of broom, when it
appears, amplifies the reduction of orthopteran density and
diversity, as only a few Ensifera species persisted in this formation. Another possible extrinsic explanation could be the
loss of oviposition sites, required by most species (Uvarov,
1977). This would concord with the preference of most
Orthoptera for open formations (Chapman and Joern, 1990).
Other extrinsic factors might play a role in decreasing species
diversity, such as increased parasitism, epizootic disease and
predation.
As for intrinsic cause, some late colonising species reach
high densities and have a mechanism against the settlement
of new species, and even eliminate several yet established
species. For example, the arrival of the ant Pheidole megacephala in Queensland sand mines results in a streaking collapse of ant diversity (Majer, 1989). Lack (1976 in Blondel,
1979), talking with birds, put forward several factors linked
to the internal organisation of the community. But the
mechanism involved in the force against colonization
remained obscure. We have shown that insect density continuously increases in the course of colonisation (Picaud
and Petit, 2007). Our experimental approach brings the idea
that, at least in prairies, high densities of insects in ‘‘medium’’ to ‘‘old’’ class herbaceous habitats reduce the arrival
of late colonising species. As a consequence, the settlement
of a new species becomes increasingly more difficult from
the medium succession stage (from about the 3rd year) onwards. It should be noted that the arrival and settlement
of new species at that stage by jumping flight is unlikely,
as all the species of sere 3 are poor flyers. In the case of
C. parallelus, our results suggest that the presence of C. biguttulus induces a stress, resulting in reduction of walking, as
C. parallelus has a weak opportunity to hide in the grass.
However, the mechanism by which the inhibition of insect
displacement would occur needs further study, and visual,
olfactive and auditive clues have to be addressed.
Table 5 – Variance ratios of C. parallelus in the presence of various densities of C. biguttulus. N.S.: non-significant, *: P < 5%,
**: P < 1%, ***: P < 1&. The combination 1–2 means that we calculated the variance ratio corresponding to C. parallelus
displacement between the situations 1 (C. biguttulus density [ 1 mL2) and 2 (C. biguttulus density [ 2 mL2)
Density of C. biguttulus
(indiv m2)
0
1
2
3
Individual
numbers of
C. biguttulus
Individual
numbers of
C. parallelus
Variance
(displacement
of C. parallelus)
0
30
60
90
143
54
60
60
97,762.12
113,105.5
53,130.46
47,080.32
Variance ratios
0
1
2
3
–
1.16 N.S.
1.84 **
2.08 ***
–
2.13 **
2.40 ***
–
1.13 N.S.
–
66
acta oecologica 32 (2007) 59–66
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