Leafhoppers (Hemiptera, Auchenorrhyncha) in fragmented habitats

8 Pages·2002·0.71 MB·English

by  Biedermann, Robert

© Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at
Leafhoppers (Hemiptera, Auchenorrhyncha) in
fragmented habitats
R. BIEDERMANN
Abstract
The distribution of leafhoppers (inclu- patterns in the habitat patches, in most
ding planthoppers, spittlebugs and tree- leafhopper species effects of area and iso-
hoppers) largely depends on the distribu- lation on density and occupancy were
tion of their host plants. Plants occur reported. Increasing patch area often
more or less aggregated and frequently resulted in higher densities and higher
form discrete patches. In natural as well as incidences. On the other hand, increasing
in cultural landscapes these patches may isolation was found to reduce the inciden-
be fragmented to some extent. A review of ce in the patches. The relevance of these
existing studies on leafhopper populations results are discussed in the light of recent
in fragmented landscapes summarises the metapopulation theory.
current knowledge on the role of area and
isolation on occurrence and density of
Key words: Auchenorrhyncha, host
leafhoppers. Whereas little information is
plant, habitat fragmentation, area, isola-
available on the dynamics of occupancy
tion
Denisia 04,
zugleich Kataloge des OÖ. Landesmuseums,
Neue Folge Nr. 176 (2002), 523-530
523
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Introduction The analysis of leafhopper communities may
yield additional information on, for instance,
The overall feature of leafhoppers (inclu- species richness or trophic interactions in rela-
ding planthoppers, spittlebugs and treehop- tion to habitat configuration (e.g. DENNO &
pers) is their close relation to plants. The host
RODERICK 1991).
plants provide nutrition (e.g. BACKUS 1985,
There a two major theoretical concepts
COBBEN 1988), shelter for eggs (e.g. CLARIDGE
dealing with the explanation of animal distri-
et al. 1977) and transmission channels for bio-
butions on islands or habitat patches. The
acoustic signals (e.g. MlCHELSEN et al. 1982).
theory of island biogeography (MACARTHUR
Accordingly, one major requisite of leafhopper
& WILSON 1967) predicts species numbers on
habitats is the presence of the host plants. In
islands or habitat patches in relation to isola-
particular in host plant specialists among leaf-
tion and area. In leafhoppers, the theory of
hoppers the habitat is principally given by the
island biogeography was studied, for instance,
distribution of the host plants.
by NlEDRINGHAUS (1991) on dune islands in
Plants frequently occur aggregated to some
the North Sea. The application of island bio-
extent and form discrete patches. The amount
geography theory is confined to communities
and physiology of the host plant may largely
and seems not suitable for the analysis of
determine the quality of such host plant pat-
populations of single species (see HANSKI
ches (e.g. PRESTIDGE 1982, MOON et al. 2000).
2001). Further, it assumes a mainland as a
However, some leafhopper species exhibit
source of colonising individuals. In fragmen-
more complex habitat requirements. Additio-
ted landscapes there is not necessarily a main-
nal factors like host plant architecture, vege-
land, but a situation with a large number of
tation structure or microclimate may be rele-
patches of similar area may occur. The corre-
vant (e.g. CLARIDGE 1986, DENNO & RODE-
sponding theory for populations on regional
RICK 1991) and therefore the habitat may be
scales is the metapopulation theory (HANSKI
not primarily defined by the occurrence of the
1998). Recent metapopulation theory is a spa-
host plants. In these species as well as in more
tially explicit attempt to describe the dyna-
generalist species with a broader range of host
mics of a regional population with its members
plants, the habitat patches may not be clearly
distributed over a set of habitat patches. The
delimited in the field. In contrast, in host
main feature of metapopulation dynamics is
plant specialists among the leafhoppers the
the occurrence of extinction and colonisation
survey of the distribution of the host plant was
events in the habitat patches.
found to be a very feasible way to determine
all potential habitats of a certain species in a The objective of this review is to make a
landscape (DENNO et al. 1981, BIEDERMANN survey on existing studies on leafhopper popu-
2000). lations in fragmented habitats and to discuss
the results in regard to metapopulation theory.
In natural as well as in cultural landscapes
According to recent theory, the occurrence
the habitats of leafhoppers are frequently frag-
and density of leafhoppers in a particular habi-
mented to some extent. In the recent two
tat patch may depend on area, isolation, qua-
decades there is increasing concern about
ongoing habitat fragmentation by human lity and surrounding landscape structure of the
activities, especially in cultural landscapes patch. The quality of a patch is the funda-
(SETTELE et al. 1996). Fragmentation is sugge- mental factor for the survival and reproduc-
sted to be one major cause of the extinction of tion of leafhoppers and is not a particular issue
species and thereby declining biodiversity of fragmented habitats. The role of surroun-
(MORRIS 1995). Looking at existing results on ding landscape structure on leafhopper distri-
leafhoppers in fragmented habitats there are bution in habitat patches is largely unknown
two levels of consideration, the population (but see JONSEN & FAHRIG 1997). Thus, in the
level and the community level. At the popu- following the current knowledge on the role of
lation level the occurrence, abundance and area and isolation on occurrence and density
dynamics of particular species is of interest. of leafhoppers will be summarised.
524
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Habitat fragmentation and
MANN 1997, BIEDERMANN 1998, ZABEL &.
metapopulation theory
TSCHARNTKE 1998, BIEDERMANN 2000, BLE-
DERMANN unpubl. data). The main focus of
Habitat fragmentation describes the
these studies was on the dependency of the
decrease in number and size of suitable habi-
incidence (= probability of occurrence) and
tats for species (e.g. HARRISON & BRUNA
density of a particular species on area and iso-
1999, HUXEL &. HASTINGS 1999). The proces-
lation of patches. In nearly all studies the first
ses which lead to habitat fragmentation are
step was a complete survey of the host plant
decreasing area of patches up to their comple-
patches in the study area providing the area
te elimination and consequently increasing
and isolation of the patches. This step was fol-
isolation of patches. The term fragmentation
lowed by a survey of the leafhopper occurren-
describes both the processes and the outcome.
ce or density in these patches. In order to
It often implies a loss of habitat due to human
quantify extinction or colonisation events in
activities. As in natural landscapes suitable
some studies the survey for the occurrence of
habitat may be patchy without anthropogenic
species has been repeated for several years or
influence, here the term patchiness may be
generations.
more appropriate. However, in the following
the term fragmentation will be used for both
Incidence and area
fragmented and patchy habitats.
The first study on the relationship bet-
Living in such a set of patches animals
ween the occurrence of leafhoppers and the
build up structured populations (HARRISON
area of their habitats was performed by HALK-
1991), with its members distributed over a
KA et al. (1971) on the spittlebug Philaenus
number of habitats. In recent years the analy-
spumarius (Aphrophoridae). They were analy-
sis of spatial population structure has made a
sing the distribution of Philaenus spumarius in
rapid development, both in theoretical (e.g.
island habitats in an archipelago of 135 islands
HANSKI 2001) and empirical studies (e.g.
in the Baltic Sea.
GUTIERREZ et al. 2001). The results suggest
A method to analyse the role of patch area
that animals build up a wide continuous range
on the occurrence of leafhoppers in host plant
of spatial population structures from isolated
patches is the use of incidence functions
patches with virtually no immigration, over
(ADLER & WILSON 1985, TAYLOR 1991).
metapopulations with a limitation in the
Incidence functions quantify the relationship
dispersal between patches, up to patchy popu-
between species presence and area in a set of
lations with high colonisation and thus low
patches of various area. In order to calculate
extinction rates (HARRISON 1991, THOMAS &
incidence functions, in each patch the presence
KUNIN 1999). According to metapopulation
or absence of the species is recorded. The
theory (HANSKI 1998) the dynamics of the
resulting occupancy patterns are related to
occurrence of a species in its habitat patches is
patch area using logistic regression (HOSMER
determined by local extinction and colonisa-
& LEMESHOW 2000). Logistic regression is a
tion. The extinction rate is assumed to decrease
statistical method which detects relationships
with increasing patch area and the colonisa-
between a dependent binary variable and one
tion rate depends on the degree of isolation of
or more independent variables. Here, the
a patch. For the long-term persistence of a
dependent variable is the presence-absence
metapopulation an equilibrium between
pattern in the patches and the independent
extinction and colonisation is required.
variable is the area of the patches. The resul-
ting incidence functions show the relationship
Leafhopper populations in
between the probability of occurrence (= inci-
fragmented habitats
dence) and area (Fig. 1).
The distribution of species in a number of In order to obtain the incidence function
habitat patches of various area and isolation of Philaenus spumarius a re-analysis of the data
was analysed in several studies on leafhoppers (HALKKA et al. 1971) was performed. The
(HALKKA et al. 1971, LAWTON 1978, RAUPP & results showed a positive relationship between
DENNO 1979, DENNO et al. 1981, MACGARVIN the occurrence of Philaenus spumarius and the
1982, BIEDERMANN & APPELT 1996, BIEDER- suitable habitat area on the islands.
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Fig. 1: Directly using the technique of logistic was increasing with increasing area of the host
Examples of incidence functions of (a)
regression, BIEDERMANN & APPELT (1996) cal- plant patches. In a second study of the tree-
Gargara genistae and (b) Ribautodel-
phax pungens demonstrating the posi- culated incidence functions of five monopha- hopper Gargara genistae in another landscape
tive relationship between the inciden- gous leafhoppers occurring in host plant pat- with 237 patches of Sarothamnus scoparius a
ce (= probability of occurrence) and similar result was found (BIEDERMANN unpubl.
ches of various area in fragmented dry grass-
area (= patch size), based on logistic
data), the incidence is increasing with increa-
regression using data from BIEDERMANN land: the leafhopper Adarrus multinotatus
sing patch area (Fig. 1). These results indicate
(unpubl.) and BIEDERMANN & APPELT (Cicadellidae), the spittlebug Neophilaenus
(1996). a high variability in the incidence-area relati-
albipennis (Aphrophoridae) in 506 patches,
onship among species, even within one guild.
the planthopper Ribautodelphax pungens (Del-
In a study of several phytophagous and
1 0- predatory insects on Urtica dioica ZABEL &.
TSCHARNTKE (1998) recorded a positive relati-
onship between the area of the host plant pat-
0.8-
ches and the incidence of the monophagous
/ / leafhopper Macropsis scutellata (Cicadellidae).
In general, the effects of patch area are of
0.6-
a /
e / b relevance for the explanation of the distribu-
c
n tion of leafhoppers as in all species a significant
e
d
ci 0.4- relationship exists between incidence and
n
I area. In order to analyse the differences in the
incidence-area relationship between species,
0.2- from the existing results area thresholds were
calculated. Based on the incidence functions
area thresholds were taken as a measure of the
0.0-
characteristic of the incidence function. As
10 100 1000 10000 100000
thresholds the area at an incidence of 0.5 and
Area [m2]
0.95 were chosen. The comparison shows a
high variability among species (Table 1).
Table 1: Some species like the leafhopper Adarrus mul-
Comparison of the area requirements (in m2)
tinotatus or the planthopper Kelisia haupti
of eight leafhopper species for two given
incidence thresholds (I = 0.5 and I = 0.95), occupy even very small patches of only a few
calculated by incidence functions using logi- square meters, whereas in other species like
stic regression; references: 1: BIEDERMANN &
the spittlebug Neophilaenus albipennis or the
APPELT (1996), 2: ZABEL & TSCHARNTKE (1998),
planthopper Ribautodelphax pungens only large
3: recalculated from HALKKA et al. (1971),
4: BIEDERMANN (unpubl. data). patches have a considerable incidence.
Species Number of patches Incidence
0.5 0.95
Adarrus multinotatus^ 506 8
Kelisia haupti* 21 10 18
Garqara qenistae* 24 24 79
Philaenus spumarius3 135 56 301
Garqara qenistae* 237 75 212
Macropsis scutellata2 32 493 1229
Neophilaenus albipennis* 506 747 1976
Ribautodelphax pungens* 73 4162 10052
phacidae) in 73 patches of Brachypodium Density and area
pinnatum, the planthopper Kelisia haupti The relationship between the density and
(Delphacidae) in 21 patches of Carex humilis the area of host plant patches was analysed in
and the treehopper Gargara genistae (Membra- several studies on leafhoppers (Table 2). In
cidae) in 24 patches of Sarothamnus scoparius. the planthopper Ditropis pteridis (Delphaci-
In all species a significant relationship exists dae) a positive relationship was detected
between incidence and area. The incidence between density and patch area of the host
526
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plant Pteridium aquilinum (LAWTON 1978). In dence was significantly affected by isolation,
a guild of leafhoppers on Spartina patens RAUPP increasing distance to the next occupied patch
&. DENNO (1979) and DENNOetal. (1981) repor- was reducing the probability of occurrence in
ted high variability in the response of species the patches.
density on patch area. A positive relationship
In contrast, in other leafhopper species no
between area and density was found in the
effect of isolation could be detected. The spa-
planthoppers Tumidagena minuta (Delphaci-
tial analysis of the distribution of the leafhop-
dae), Delphacodes detecta (Delphacidae) and
per Adarrus mulanotatus showed no effect of
Aphelonema simplex (Issidae), whereas the
isolation on the occupancy in the patches of
densities of the planthopper Megamelus lobatus
the host plant Brachypodium pinnatum (BlE-
(Delphacidae) and the leafhoppers Amplice- Table 2: Summary of the results on
DERMANN 1997). In a set of 506 patches even
phalus simplex (Cicadellidae) and Destria bisig- the relationship between leafhopper
patches with large distances to other patches density and patch area, +: positive,
nata (Cicadellidae) were not affected by area.
had a high incidence. In the leafhopper 0: no relationship; references:
In a study of the density of the spittlebug Macropsis scutellata isolation had no effect on 1: LAWTON (1978), 2: RAUPP & DENNO
Philaenus spumarius in 24 patches of Chameri- (1979), 3: DENNO et al. (1981), 4: MAC-
the incidence in 32 patches of Urtica dioica
on angustifolium no significant relation could GARVIN (1982), 5: BIEDERMANN (1997),
(ZABEL & TSCHARNTKE 1998). 6: BIEDERMANN (unpubl. data).
be detected between area and density (MAO
GARVIN 1982). In the leafhopper Adarrus mul-
Species Number of patches Density-area
tinotatus no correlation was found between relationship
density and patch area in 14 patches of Ditropis pteridis'1 9 +
Brachypodium pinnatum (BIEDERMANN 1997). Delphacodes detecta2 25 +
Tumidagena minuta3 25 +
A similar result was obtained in the treehop-
Aphelonema simplex3 25 +
per Gargara geniswe. There was no relations- Amplicephalus simplex3 25 0
hip between density and patch area in 17 pat- Destria bisiqnata3 25 0
Meqamelus lobatus3 25 0
ches of Sarothamnus scoparius (BIEDERMANN
Philaenus spumarius* 24 0
unpubl. data). Adarrus multinotatus5 14 0
Gargara genistae6 17 0
Incidence and isolation
Species Number of patches Incidence-isolation
Among the existing investigations on the relationship
spatial distribution of leafhoppers in habitat Philaenus spumarius^ 135
patches no study was available on the relati- Neophilaenus albipennis* 506
Gargara genistae^ 237 _
onship between density and isolation. Howe- Adarrus multinotatus2 506 0
ver, there are a few studies testing the effect of Macropsis scutellata3 32 0
isolation on the occupancy of patches (Table
Table 3: Summary of the results on
3). The analysis of Philaenus spumarius on Incidence, area and isolation the relationship between leafhopper
small islands in the Baltic Sea (HALKKA et al. incidence and patch isolation, -: nega-
The simultaneous analysis of both area tive, 0: no relationship; references:
1971) showed a significant effect of isolation
and isolation of the patches was performed in 1: HALKKA et al. (1971), 2: BIEDERMANN
on the distribution of the spittlebug. In a stu- (1997), 3: ZABEL & TSCHARNTKE (1998),
three species. In the spittlebug Neophilaenus
dy of the spittlebug Neophilaenus albipennis 4: BIEDERMANN (2000), 5: BIEDERMANN
albipennis both factors have a significant effect (unpubl. data).
BIEDERMANN (1997) was using logistic regres-
on the occurrence in the host plant patches.
sion (as the independent variable the distance
These two factors yet account for 27.2 % of
to the next occupied patch was used as a mea-
the variance in the occurrence when analysed
sure of isolation) to detect effects of isolation
in a multiple logistic regression analysis (BlE-
on the incidence of the spittlebug in the 506
DERMANN 1997). That is, even without consi-
patches of its host plant Brachypodium pinna-
turn. The results clearly state that the inciden- dering habitat quality of the patches a rather
ce of Neophilaenus albipennis was reduced in high amount of variance was explained by
the more isolated patches. Another study these two factors of spatial configuration. In
using logistic regression was performed in the the treehopper Gargara genistae the relation-
treehopper Gargara genistae in a set of 237 pat- ship between occurrence and these two factors
ches of the host plant Sarothamnus scoparius was similar. The amount of variance explained
(BIEDERMANN unpubl. data). Again, the inci- was 25.4 % (BIEDERMANN unpubl. data).
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Using the same statistical procedure in ano- reduce the extinction risk due to environ-
ther spittlebug, Phiiaenus spiimariiis, in the mental stochasticity (LANDE 1993). Additio-
joint analysis of area and isolation of patches nally, the resource concentration hypothesis
(data from HALKKA et al. 1971) these two fac- (ROOT 1973, CONNOR et al. 2000) predicts
tors even account for 57.5 % of the variance higher densities in larger patches as a result of
in the distribution. e.g. greater reproduction, reduced edge effect
or reduced predator density.
Dynamics of incidence On the other hand, dispersal could obscu-
re the correlation between density and area. In
Surveys of the distribution of species in
species with a high dispersal ability like Ampli-
several subsequent years or generations yield
cephalus simplex or Adarrus multinotatus, all
the dynamics of patch occupancy. The species
patches could be reached with high probabili-
may get extinct in some patches and other
ty. Thus, initial differences in densities due to
previously empty or new patches may be (re-)
reduced performance in small patches may be
colonised. Metapopulation theory suggests
levelled off by dispersing individuals. As a
that the extinction rate of species depends on
result, small patches may be sink-habitats
patch area. In fact, in the spittlebug Neophila-
(PULLIAM 1996). The outcome of such a pro-
enus albipennis the extinction rate is positively
cess would be an equal density in all patches
correlated with patch area (BIEDERMANN
irrespective of its area. In fact, for the guild of
2000). The extinction rate is high in small
leafhoppers on Spartina patens DENNO et al.
patches and decreases with increasing patch
(1981) suggest an association between positi-
area. The mean yearly rate of extinction was
ve area-density relationship and low dispersal
estimated 3.9 %. The colonisation rate was
ability of species (e.g. measured by the fraction
comparable, the yearly rate was 4-9 %. The
of macropterous individuals).
treehopper Gargara genistae showed a compa-
rable turnover in patch occupancy (BIEDER- The dispersal ability differs between spe-
MANN unpubl. data) with a shifted balance cies and may be correlated with the effect of
between the yearly extinction rate (11.1 %) isolation on the distribution in fragmented
and the yearly colonisation rate (1.9 %). In landscapes. Dispersing individuals may (re-)
the spittlebug Cercopis sanguinolenta in a colonise patches which were empty or newly
three-years period no extinction was recorded emerged. For instance, in the spatial analysis
in ten local populations (BIEDERMANN 1998). of the distribution of the leafhopper Adarrus
Obviously, the yearly rate of extinction varies multinotatus no effect of isolation on patch
among leafhopper species. However, the data- occupancy could be detected. In the same
base is to weak to deduce general conclusions landscape a parallel investigation of the popu-
from these results. lation genetics of Adarrus multinotatus was
conducted. The results showed a concordant
result, a high gene flow is suggested to exist
Synthesis
between local populations at the regional sca-
le (VEITH et al. 1996). In the spittlebug Neo-
The fragmentation of habitats may have
philaenus albipennis which was studied in the
severe consequences on animal distribution
same set of habitat patches, the distribution
(HARRISON & BRUNA 1999). Fragmentation
was significantly affected by isolation. As
leads to reduced patch area and as a result the
expected, in a mark-recapture experiment in
extinction probability of local populations is
Neophilaenus albipennis low dispersal rates were
high in small patches. Below a certain thres-
recorded (BIEDERMANN 1997).
hold a patch may be too small to maintain via-
ble populations. The comparison of studies on The existing case studies on leafhoppers
leafhoppers demonstrated that the area requi- clearly demonstrate the effects of area and iso-
rements vary in a broad range. This variability lation on distribution and density in fragmen-
may be attributed to parameters of population ted habitats. A set of hypotheses is available to
dynamics or life-history traits. Species which explain these static patterns. However, these
are able to build up high densities in their pat- studies give only an idea of the importance of
ches could reach sufficient population sizes to dynamic spatial processes. In particular, stu-
528
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