Analele Științifice ale Universității „Al. I. Cuza” Iași, s. Biologie animală, Tom LV, 2009
THE DIVERSITY INDICES APPLIED TO THE MAYFLY (EPHEMEROPTERA) COMMUNITY OF BUZAU RIVER Oana RISTEA Romania Water Administration – Buzău Directorate, Str. Bucegi 20 bis, Buzău,
[email protected]
Abstract. This study aimed at comparing the results obtained by calculating a several α diversity indices (Shannon-Wiener, Simpson and Evenness) and Cody`s index for β diversity, during 3 years of study (20052007). The diversity of mayfly comunity have been study at 7 sites begining with the spring area of Buzău river towards the mouth in the Siret river. 33 species have been recorded in a 63 samples collecting during the study period years of study. Analysing the each index values we can see a variation in longitudinal plan (from spring to mouth zone) but also a clear seasonal dynamics. The diversity indices had low values in the 2 last sites, especially in the samples from 2005. Keywords: mayflies, diversity, Shannon-Wiener index, Simpson index, Evenness, Cody`s index. Rezumat. Aplicarea unor indici de diversitate în comunitatea de efemeroptere (Ephemeroptera) a râului Buzău. Scopul acestui studiu este acela de a compara rezultatele obținute prin calcularea unor indici ai diversității α (Shannon-Wiener, Simpson și echitabilitatea) și indicele Cody pentru diversitatea β în cei trei ani de studiu (2005-2007). Diversitatea comunității de efemeroptere a fost studiată în 7 stații fixate pe cursul râului Buzău de la izvor până la vărsare în Siret. Au fost identificate 33 de specii în cele 63 de probe recoltate. Analizând valoarea fiecărui indice s-a constatat variația în plan longitudinal dar și o dinamică sezonieră evidentă. S-a constat valori scăzute ale indicilor de diversitate în ultimile două stații în special în probele din 2005. Cuvinte cheie: efemeroptere, diversitate, indicele Shannon- Wiener, indicele Simpson, echitabilitatea, indicele Cody.
Introduction Diversity had two components: species richness, the number of species in the community, and evenness, the number of inviduals in each. Diversity had an important role in evolutional processes which have generated the whole variety of the world, being an indicator of an ecosystem stability (Washington, 1984). The use of the diversity indices for the monitoring of the water quality is based on the concept that the structure of the invertebrates community may be changed by any environment disturbance. Using of the diversity indices trys to combine the data regarding the organism abundances and to gather the information in a single numerical value. As bigger the index is, as stable the biocenosis is, composed of a big number of species. According to Washington (1984), a number of diversity indices are used for the evaluation of an ecosystem status: dominant indices which are sensitive to the abundance of the most common species rather than to species richness (Simpson index, 1949); indices which depend of the number of species in concordance with individuals number (Margalef index 1958, Menhinick index, 1964); indices which permits the application of the information theory (Shannon-Wiener index, 1949) which take into account that two components of the diversity: species number and their equitability. The diversity of any organism community from a habitat is called “α” diversity, which express the wealth in species, the number of individuals, the heterogenity of the individuals distribution and the biomass.
-27-
Oana Ristea
When we analyze the change of the diversity along the stream gradient (latitude, altitude etc.), we are talking about “β” diversity. The data were processes according to Cody`s measure of “β” diversity (Cody, 1975). This index is used to evaluate how species diversity changes along a gradient (Ravera, 2001). Materials and methods The Buzău river is one of the most important tributary of the Siret river and is 302 km long. (Fig. 1). Buzău river crosses mountains, hills and plains, from the peaks of Ciucaș to the Bărăgan plain. Geology is mainly silicious but also an organic and a reduced calcareous one. The distribution of precipitations and temperatures varies with the altitude. Thus the precipitations quantity varies between 400 mm/year and 1200 mm/year and the mean annual temperature is between -40 C in the mountains and 1000 C in the plain.
Figure 1. Buzău River sampling sites. Quantitative samples of benthos were collected from seven monitoring sites: Vama Buzăului, downstream Siriu reservoir, Nehoiu, Măgura, upstream Buzău, Banița, Racovița, between 2005-2007 through seasonal samples in March, July and September. Physico-chemical conditions at each station were also monitored during each collection period. The quantitative benthic samples were sampled with a Surber sampler with a surface of 900cm2. The benthic macroinvertebrates identification was done till the species level. 33 species of mayflies were collected in the area surveyed. Results and discussion As it was expected, mayfly communities respond to natural change of environmental factors as well as to human impacts along the Buzău River. The diversity is -28-
Analele Științifice ale Universității „Al. I. Cuza” Iași, s. Biologie animală, Tom LV, 2009
increasing from the spring towards the middle section, with Aval Acumulare Siriu site exception, were the values considerably decrease under the influence of Siriu dam. As we can see from the table 1, the H` index values are between 2.12 and 0.65, without taking into account the sites where the indice values were 0. As well as we can see that the biggest H values are in Vama Buzăului, Nehoiu and Măgura sites and the low values of the indice are in the last 3 sites and in Aval Acumulare Siriu site because of the Siriu dam influence. Table 1. The H` index values in all 3 years of study.
Shannon- Wiener Index
Vama Buzăului
Aval Acum. Siriu
Nehoiu
Măgura
Am. Mun. Buzău
Banița
Racovița
Media
Mar.05
1.56
1.34
1.09
1.42
1.42
0.68
0.00
1.07
Jul.05
2.08
1.06
1.67
1.65
1.79
1.09
0.00
1.33
Sep.05
1.98
1.06
1.58
0.78
0.80
0.66
0.00
0.98
Mar.06
1.68
1.04
1.30
1.35
1.22
0.69
0.65
1.13
Jul.06
1.89
1.53
1.97
1.76
0.98
1.33
1.36
1.55
Sep.06
1.71
1.37
1.96
2.12
1.44
1.59
1.38
1.65
Mar.07
1.78
1.26
1.60
1.37
1.10
1.04
0.68
1.26
Jul.07
1.23
1.00
1.37
1.54
1.89
0.65
1.28
1.28
Sep.07
1.66
1.34
1.08
1.23
1.09
0.69
1.04
1.16
We can see in the next graph (Fig. 2) longitudinal variation of the H` index values in all those 3 study years. We can find out also from this graph the high values of the first 3 sites excepting the site downstream the dam. This H` values are the highest in 2006 year because this year is normally from meteorological point of view. The H` index values follow the same trend in 2005 and 2007, fact which shows that extreme hydrological changes determined by special meteorological conditions (flood in 2005 and drought in 2007) have caused the same answer on the part of invertebrates community.
Figure 2. Longitudinal variation of H` index in all 3 years of study. -29-
Oana Ristea
The dynamics of the H` indice average value in all 9 sampling sampling periods shows that the lowest value was in September 2005 (0.98) and the highest in September 2006 (1.65). It can see very well also from this graph of the H indice dynamics, the influence of the meteorological conditions on diversity (Fig. 3).
Figure 3. The dynamics of the H` indice in Buzau River.
Evenness (E) mesured wih Pielou indice (Pielou, 1969) is the expresion of the way through which a species is represented in a biocenoza and it shows how a number of individuals are distributed equally into species (Table 2). The values of evenness are between 0.79 to Măgura and Amonte Municipiu Buzău in July 2005 and 0.99, value registered in more sites and sampling periods. Table 2. The Evenness indices values in all 3 years of study.
Evenness
Vama Buzăului
Aval Acum. Siriu
Nehoiu
Măgura
Am. Mun. Buzău
Racovița
Media
Mar.05
0.80
0.96
0.99
0.93
0.88
Banița 0.81
0.00
0.77
Jul.05 Sep.05 Mar.06 Jul.06 Sep.06 Mar.07
0.95 0.90 0.93 0.82 0.87 0.99
0.93 0.96 0.94 0.95 0.99 0.90
0.86 0.81 0.94 0.95 0.94 0.99
0.79 0.92 0.97 0.84 0.96 0.99
0.79 0.92 0.95 0.89 0.89 0.99
0.97 0.99 0.99 0.96 0.99 0.95
0.00 0.00 0.94 0.98 0.99 0.98
0.76 0.75 0.97 0.94 0.95 0.97
Jul.07
0.88
0.90
0.98
0.96
0.97
0.93
0.92
0.94
Sep.07
0.92
0.96
0.98
0.89
0.99
0.99
0.95
0.95
We have represented graphically the average values of the equitability and Shannon diversity index in order to analyze the dynamics of this indicator during the study period and we have seen a negative correlation of those two indices, which means that there where the number of species is increasing, they are represented by an unequal and variable number of individuals (Fig. 4).
-30-
Analele Științifice ale Universității „Al. I. Cuza” Iași, s. Biologie animală, Tom LV, 2009
Figure 4. The dynamics of the H` indice and evenness in Buzau River.
Simpson diversity index (Ds), calculated as a difference (D=1-S), shows the dominance of a species or of a species from an ecosystem, as closer to 1 the values are, the bigger diversity is. Simpson diversity index has high values between 0.87-0.65 in Vama Buzăului, Nehoiu and Măgura sites, comparing with the other sites in which Ds indice has low value (0.38) (Banița in March 2005), without taking into account Racovița site where the indice values were 0 in 2005. Table 3. The Ds index values in all 3 years of study.
Simpson Index
Vama Buzăului
Aval Acum. Siriu
Nehoiu
Măgura
Am. Mun. Buzău
Banița
Racovița
Media
Mar.05
0.73
0.72
0.66
0.70
0.59
0.38
0.00
0.54
Jul.05
0.86
0.61
0.75
0.68
0.68
0.48
0.00
0.58
Sep.05
0.84
0.64
0.74
0.78
0.80
0.66
0.00
0.64
Mar.06
0.80
0.63
0.71
0.73
0.66
0.49
0.46
0.64 0.75
Jul.06
0.81
0.77
0.85
0.79
0.60
0.72
0.73
Sep.06
0.78
0.74
0.84
0.87
0.72
0.79
0.74
0.78
Mar.07
0.83
0.68
0.79
0.74
0.66
0.63
0.49
0.69
Jul.07
0.68
0.59
0.74
0.77
0.84
0.46
0.70
0.68
Sep.07
0.79
0.73
0.65
0.68
0.66
0.49
0.63
0.66
Thus, following the average values of Ds indice in all 7 sites during 3 study years (Fig. 5), we see the same variation of the indice in longitudinal plan, with a decrease of the values in the sites situated after Siriu dam and in the sites with an degradation of the biotope conditions (hydromorphological, hydrological and chemical) namely Amonte Municipiul Buzău, Banița and Racovița.
-31-
Oana Ristea
Figure 5. Longitudinal variation of Ds index in all 3 years of study.
Regarding Ds indice dynamics (Fig. 6) we can see a seasonal variation, the values being higher in July and September sampling periods.
Figure 6. The dynamics of the Ds index in Buzau River.
Regarding β diversity expressed through Cody`s index, it takes the average values listed in table 4. We can see that these data shows that the diversity longways a gradient presents a seasonal variation (Fig. 7), decresing in spring and increasing in summer, because of the reproduction, adults emergence or biotop conditions.
-32-
Analele Științifice ale Universității „Al. I. Cuza” Iași, s. Biologie animală, Tom LV, 2009
Table 4. The Cody`s index values in all 3 years of study.
Mar 05 Jul 05 Sept 05 Mar 06 Jul 06 Sept 06 Mar 07 Jul 07
Cody`s index 2.00 2.42 3.08 2.08 3.98 4.42 2 3.5
Sep 07
2.92
Figure 7. The dynamics of the Cody`s index in Buzău River.
Conclusions Analysing all 4 indices we can figure that there is a big variability in time in the same site as well as from one site to another. The low values for the majority of the indices were in March and in 2005 and 2007 years. References Cody, M., 1975. Towards a theory of continental species diversity bird distribution over Mediterranean habitat gradients. In Ecology and evolution of communities. Harvard Univ. Press, Cambridge, Mass., 214257. Ravera, O., 2001. A comparison between diversity, similarity and biotic indices applied to the macroinvertebrate community of a small stream: the Ravella river (Como Province, Northern Italy). Aquatic Ecology, 35: 97-107. Washington, H., 1984. Diversity, biotic and similarity indices: a review with special relevance to aquatic ecosystems. Water Research, 18: 653-694.
-33-