Effects of climatic factors on yearly population sizes of Isophya costata (Orthoptera) [628122]

NORTH-WESTERN JOURNAL OF ZOOLOGY 14 (1): 13-16 ©NWJZ, Oradea, Romania, 2018
Article No.: e171102 http://biozoojournals.ro/nwjz/index.html

Effects of climatic factors on yearly population sizes of Isophya costata (Orthoptera)

Zoltán KENYERES1*, Gábor TAKÁCS2 and Norbert BAUER3

1. Acrida Conservational Research L.P., Deák F. street 7, 8300 Tapolca, Hungary.
2. Fertő-Hanság National Park Directorate, Ré v-Kócsagvár, 9435 Sarród, Hungary.
3. Hungarian Natural History Museum, Department of Botany, Könyves K. krt. 40, 1087 Budapest, Hungary.
*Corresponding author, Z. Kenyer es, E-mail: [anonimizat]

Received: 10. March 2017 / Accepted: 18. May 2017 / Available online: 29. July 2017 / Printed: June 2018

Abstract. Isophya costata , protected under EC, post-glacial ende mic relict in the Carpathian Basin, is an important indicator species of
dicot-rich hayfields and steppe grasslands. Significant changes in yearly population sizes of I. costata were observed in its area-
margin. Based on this, population dynamics and habitats of I. costata have been monitored between 2007 and 2014. Our results
showed that annual population sizes were heavily affected by macroclimatic factors in March – monthly precipitations below 25
mm or above 55 mm had been found as a negative impact on yearly densities of the species.

Key words: Isophya costata, density, macroclimate, vegetati on, habitat-structure.

Introduction

Isophya costata Brunner von Wattenwyl, 1878, a subendemic
post-glacial relict species of the Carpathian Basin, is pro-
tected under EC and national legislation. Its known occur-
rences outside Hungary are limited to the Viennese Basin (Austria) and Transylvania (Romania) (Heller et al. 2004,
Bauer & Kenyeres 2006a, Nagy & Rácz 2014).
Former studies emphasized th e continuous decline of the
species due to habitat loss and degradation caused by land
cultivation, abandonment of hay making, etc. (Nagy 1974).
During the recent decade, however, a number of new occur-
rences have been discovered as a result of systematic re-
search (Bauer & Kenyeres 2006a, Nagy & Rácz 2014).
Isophya costata can be linked to dicot-rich hayfields, fens,
steppe grasslands and loess grasslands (Nagy & Szövényi
1999, Nagy & Rácz 2014). A detailed study on habitat prefer-ences showed that the key factor determining its occurrence
was total cover of mesophytic dicots, providing the required
food source and vegetation ar chitecture (Kenyeres et al.
2004, Bauer & Kenyeres 2006a). Originally, Isophya costata
must have been a typical species of dicot-rich loess grass-
lands and closed steppe grasslands, but it had later adapted to man-made hay meadows with similar vegetation struc-
ture. Currently the majority of known populations occur in
the latter anthropogenic habitats and much less steppe grass-
land and loess grassland popula tions remained (Kenyeres et
al. 2004, Bauer & Kenyeres 2006a, Kenyeres et al. 2009).
Nymphs emerge as early as in March, and the adult insects h a v e d i e d b y J u l y a t l a t e s t . T h e u n m i s t a k a b l e s o u n d o f t h e
adults can greatly help in loca ting the specimens (Heller et
al. 2004).
Population sizes of orthopterans are strongly influenced
by climatic parameters (Kemp & Sanchez 1987). Based on
that, the orthopterans are good, but as yet rarely researched
focal taxon of climate change (Cannon 1998). In relation this,
macroclimatic requirements of I. costata have also not been
studied yet.
Population and habitat conditions of I. costata in the Lake
Fertő region have been studied since 2007 within a monitor-
ing program of Fert ő-Hanság National Park Directorate.
During our research, significan t changes in yearly popula-
tion size were observed. Question of our study was that yearly population size reflects just the abundance of avail-able mesophytic dicots, or affected also by climatic condi-
tions during hatching and the early nymphal period.

Study area and methods
The sampling sites were situated in a grassland area, 150–400 meters west of Lake Fert ő (Sopron: Halász-rét, elevation above sea level:
115–117 m) (Fig. 1). The surveyed habitat types included (a) a meso-phytic hay meadow / Pastinaco-Arrhenatheretum (Knapp 1954) Pas-
sarge 1964/, dominated by Arrhenatherum elatius and Dactylis glomer-
ata, Knautia arvensis, Pastinaca sativa, Ranunculus acris, Lathyrus prat-
ensis ; and (b) semi-arid mowed grasslands dominated by Bromus
erectus . The vegetation structure of selected sampling sites differed
from each other: Study site 1 wa s characterized by multi-layered
canopy dicot-rich tall grass meadow with some hydrophilic elements (e.g. Alopecurus pratensis, Cirsium canum, Symphytum officinale ); Study
sites 2 and 3 were characterized by drier habitats, dominated by
Bromus erectus , with steppe-grassl and species (e.g. Salvia nemorosa,
Festuca rupicola, Filipendula vulgaris ) favorable for I. costata .

Figure 1. Study area.

Local population of I. costata was monitored yearly from 2007 to
2014 by transect method at 3 samplin g sites (coordinates: Study site 1
– N 47.682, E 16.671; Study site 2 – N 47.685, E 16.666; Study site 3 –N
47.691, E 16.667). The species was sampled in 5 transects on each site,
each transect was 10 m long and 1 m wide. Annual sampling dates fell in the same time of the year wi th the highest expected number of
detectable fertile adults (end of Ma y to early June). Samplings were
carried out in late afternoon on wa rm rainless days through visual
detection (complited by acoustic detection). Based on census data

Z. Kenyeres et al.
14
from transects and total area of su itable habitat, we estimated popu-
lation size at ea ch sampling site.
During the project period, triennial vegetation surveys (2008,
2011, 2014) were also carried out through quadrat sampling (4×4 m quadrats, 5 quadrats in each sampling site, percentage cover esti-mates). During the surveys, vegeta tion height and the number of
vegetation layers were also record ed. To compliment these data, we
measured microclimatic conditions too. Temperature (°C) and hu-
midity (%) were measured in the quadrats at five points (at ground level and at 10, 20, 30 and 120 cm) by TESTO 615 and TESTO 625 digital hygrothermographs. To rule out possible deviations in meas-urement conditions, for the analyses we used relative values (data
measured at 120 cm subtracted from those measured at lower levels).
Macroclimatic data (monthly rainfall and mean temperatures)
were supplied by the North-Transdanubian Water Directorate (ÉDU-
VIZIG) from its Fert őrákos weather station (N47°42’52”, E16°39’54”;
average distance from sampling area: 3 km).
From the above primary data, we calculated the following sec-
ondary values: average I. costata density per square meter for each
sampling site; estimated number of adult I. costata for each sampled
habitat; total grass cover; cover of dicots; cover of mesophytic plants [based on Borhidi (1995): plant species classified as WB4 or higher];
number of plant species; ve getation species diversity.
For determination of the require ments related to macroclimate,
the following data were used: (a) monthly precipitation and tem-perature data from the first half of the given year and the prior win-ter; (b) climate data averaged in di fferent ways (for the entire winter
period from November to March, for January to March, for February to April, etc.).
Data were subjected to Pearson’ s correlation test and to linear
and polynomial regression analysis using PAST 1.95 software
(Hammer et al. 2001).
Results

Population size
During the monitoring period from 2007 to 2014, significant
changes in population size of I. costata were observed. In
2010 with extreme high Q1-Q2 rainfall and in 2007, 2009,
2012 and 2014 with extreme low sp ring rainfall, population
density was rather low (0.16–0.28 adult/m2). On the other
hand, in 2008, 2011 and 2013, with average late spring rain-
fall, density figures were much higher (0.32–0.42 adult/m2).

Correlation analysis
a) Isophya costata population and microclimate
No significant correlation wa s revealed between popula-
tion size and microclimatic data.
b) Vegetation and microclimate
In terms of vegetation and microclimate, significant cor-
relations were found between vegetation height and tem-
peratures measured at every level (T_ ground level: r = –
0.9697, p<0.001; T_10cm: r = -0.9757, p<0.001; T_20cm: r = –
0.9107, p=0.001; T_30cm: r = -0.7721, p=0.015; T_average: r =
-0.9418, p<0.001).
c) Isophya costata population and macroclimate
Pearson’s correlation test showed significant negative
correlation between population size and March mean tem-
peratures ( r = -0.7119, p=0.048). No correlation was revealed
between population size and ra infall in spite of the observa-
tion that March rainfall figures seem to influence changes in
population density and population size. Largest population sizes occurred when March ra infall was between 25 and 55
mm (Fig. 2).

Figure 2. March rainfall, March mean temperatures and density of
Isophya costata in the highest density sampling site (2007–2014)

d) Vegetation and macroclimate
Significant positive correlations were found between to-
tal vegetation cover and monthly precipitation figures in
February ( r = 0.6729, p=0.047) and May ( r = 0.6727, p=0.047);
and between vegetation height and monthly mean tempera-tures in February ( r = 0.8875, p=0.001). A significant negative
correlation was revealed between vegetation height and
monthly mean temperatures in April ( r = -0.7563, p=0.018).
e) Isophya costata population and vegetation
Pearson’s correlation test sh owed significant positive
correlations between I. costata population density and the to-
tal cover of mesophytic dicots ( r = 0.7664, p=0.016), the total
vegetation cover and the number of plant species present
(pop. size of I. costata /total cover of vegetation, r =
0.7745/p=0.014; pop. size of I. costata /species number of
plant species, r =0.9327, p<0.001).

Models used

Regression analysis was applied to variables with high cor-

Macroclimate and Isophya costata
15

Table 1. Significant results of linear (Lr) and polynomial (Pr) regression analyses (r values, p<0.5 with bold).

Density of Isophya costata Cover of mesophytic dicots
Cover of mesophytic dicots Lr: (+) 0.014 / Pr: 1.477 –
March rainfall Lr: 0.985 / Pr: 0.456 Lr: 0.694 / Pr: 1.843
May rainfall Lr: (–) 0.082 / Pr: 0.463 Lr: 0.818 / Pr: 1.844
Average humidity in the grass Lr: 0.791 / Pr: 1.805 Lr: (+) 0.429 / Pr: 1.500
Average temperature in the grass Lr: 0.839 / Pr: 0.589 Lr: 0.649 / Pr: 0.664

relation coefficient and microclimatic parameters. It revealed
a positive linear connection (best fit: linear model) between
the cover of mesophytic dicots and the population size of I.
costata and between the average humidity at grass levels and
the cover of mesophytic dicots. On the other hand, connec-
tion between March rainfall and the population size of I. co-
stata could be described by a polynomial model. Finally, the
changes of May rainfall data and the population size of I. co-
stata could be approximated by negative linear model (Table
1).

Discussion
Based on the above results and in harmony with prior ob-
servations (Kenyeres et al. 2004, Bauer & Kenyeres 2006a),
h a y m e a d o w s r i c h i n m e s o p h y t i c d i c o t s s h o u l d b e c o n s i d –
ered the optimal habitat for this species in the eastern border
zone of its distribution range. The habitat structure of hay meadows, independently of thei r geographic location, suits
the habitat preferences of sensitive grasshopper species in
several ways (Sa ğlam & Ça ğlar 2007): high relative cover of
dicots, diverse vegetation architecture, microclimate, etc. On
the other hand, we found that grass level microclimatic con-
ditions, which influence the occurrence and population size of many other orthopterans (Guido & Chemini 2000, Squitier
& Capinera 2002, Bauer & Kenyeres 2007), did not have a
significant impact on the local population size of I. costata . It
is known that the cover of mesophytic dicots has a signifi-
cant effect on grass level mi croclimate (Bauer & Kenyeres
2006b, 2007). However, the strong correlation between the population size of I. costata and the total cover of mesophytic
dicots in our data can rather be explained by specific feeding
and habitat architecture needs of the species (Kenyeres et al. 2004, Bauer & Kenyeres 2006a).
From the analyzed macroclimatic parameters, March
precipitation and mean temperatu re figures seem to have the
most impact on population size of I. costata . It can also be an
indirect relationship considering that the spring/early
summer vegetation structure (grass height, cover of dicots, etc.) of the hay meadow in the highest density sampling site
was influenced by the precipitation in March. Furthermore,
complex vegetation structure has been proven to determine
population density of species in a given site. It follows that
dry spring weather can not only be disadvantageous for hatching success but also offer suboptimal habitat conditions
for the developing insects. We found that March rainfall be-
low 25 mm or above 55 mm could be considered unfavor-able for I. costata (Fig. 2). The upper threshold can be attrib-
uted to the fact that the develo pment of eggs laid in the soil
is already going on at full speed in March (nymphs emerge in early April at latest). However, higher than optimal
March rainfall can often result in high surface water level,

Figure 3. Density of Isophya costata and cover of mesophytic dicots
in the studied quadrats (2008, 2011, 2014).

which hinders egg hatching and early larval development.
Thus, the amount of rain in Ma rch ideal for the species falls
in an optimal range, too much or too little precipitation is e q u a l l y d i s a d v a n t a g e o u s . I t i s a l s o p r o v e n b y t h e f a c t t h a t
the relationship between the concerning variables was re-
vealed by neither Pearson’s correlation test nor linear regres-sion analysis, but was shown by polynomial regression
analysis (Table 1). In terms of spring rainfall and surface wa-
ter levels, the habitat needs of the insect should come from
the fact that its primary habi tat must have been Pannonic
loess steppes before the appearance of man-made hay mead-
ows (Bauer & Kenyeres 2006a). This particular habitat type is typical of drier climates but due to its structure and species
composition, its vegetation exhibits more mesophytic traits
than expected from its geographic location.
In summary, the population size of I. costata in a given
habitat is influenced by several factors: (1) the presence of
dicots is a prerequisite for th e species’ occurrence; (2) the
appropriate amount of dicots also offers an optimal grass-
land structure in which the species can move, hide from its predators, and which ensures suitable microclimatic condi-
tions; however (3) disadvan tageous macroclimatic condi-
tions can override the two factors mentioned above.
We must note, that significan t changes in yearly popula-
tion size sometimes do occur in other I. costata populations
elsewhere in Hungary too. It calls for extending the current research, so that we can make further steps to lay the precise
foundations for successful in si tu conservation of this en-
demic European protected species.

Species conservation

Right after discovering the species in the area, we had al-ready designated a smaller part of its habitat (highest den-
sity occurrence) where hay should not be cut before July. To

Z. Kenyeres et al.
16
ensure this, we talked to th e land management supervisors
and the actual field workers several times on the spot. As a result, management practices to preserve and strengthen the
population of I. costata on this designated area have been
aptly carried out during recent years.
In terms of species conservation, it is important to note
that fluctuation in yearly po pulation size can also occur
naturally, according to our re sults. However, to prevent
population decrease due to ha bitat degradation, burning and
trampling should be avoided and, at least in a part of the
habitat, grass cutting should be in harmony with the
phenology of the species (i.e. grass should not be cut until
July, mowing grass should be in patches). In this way, a
multi-layered canopy dicot-rich grassland structure, favor-
able for the species, can be ensured.

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