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Determinants of plant species richness in different wetland types along a hydrological gradient: implication for conservation

Shi J., Ma K., Wang J., Zhang Y., Zhao J.

Polish Journal of Ecology

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2013

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Vol. 61, nr 4

645--654

EN

The loss of biodiversity caused by wetland degradation is a hot issue in ecology. It is known that hydrological degradation is the primary reason resulting in wetland degradation, but little is known about the relationship between plant species richness and environmental factors in different wetland types along a hydrological gradient. According to the gradient from high to low water level, wetland remnants in the Sanjiang Plain of northeast China were classified into three wetland types, which were permanently inundated marshes (PIM), seasonally inundated marshes (SIM) and wet meadows (WM) respectively. In this paper, we aimed to identify the determinants of plant species richness in the three wetland types and discern the transition of the determinants along a hydrological gradient. Plant species richness as well as area, habitat heterogeneity and resource availability was investigated in 51 wetland remnants, which were composed of 6 PIM, 25 SIM and 20 WM. Averagely, the area of wetland remnants occupied by PIM, SIM and WM was 0.35 ± 0.17 ha, 2.81 ± 2.88 ha and 1.34 ± 1.18 ha respectively. Aggregating the species in each wetland type, there were 67, 244 and 170 species recorded in PIM, SIM and WM. The determinants of species richness varied in different wetland types: standing water depth in PIM, area and water heterogeneity in SIM, and soil fertility and area in WM. With the decreasing water level, the influence of hydrological condition on species richness in the three wetland types declined while the impact of area and soil fertility gradually increased. Thus, hydrological condition was probably responsible for the transition of the determinants of species richness in different wetland types. Moreover, the habitat specialists of wetland would be lost when PIM or SIM degraded to WM. In order to conserve and restore plant diversity, specific measures should be taken including preventing area loss for all wetland remnants, managing the hydrological process for PIM and SIM, and regulating soil nutrient for WM.

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On species-area relationships. 2, Slope and factor values of power function and exponential model

Ulrich W.

Polish Journal of Ecology

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2000

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Vol. 48, nr 1

21-35

EN

Using model assemblages generated by a FORTRAN program the parameter values of the slope of the power function and the factor of the exponential model of species-area relationships have been studied. It appeared that the slope value is not a constant independent of area and sampling method but depends strongly on grain, sampling method and model fit. The fraction of singletons in the sample proofed to be of major importance. A plot of slope against assemblage structure (estimated by the standard deviation of log2 (densities) was bell shaped with the highest slope values at intermediate SD values. A comparison of this plot with SD values from theoretical relative abundance distributions showed that log-normal distributed assemblages should have slope values that are higher than previously reported in the literature. Although it was impossible to predict the slope from the relative abundance distribution, the opposite was possible. At any given slope value there are two linked relative abundance distributions. The factor of the exponential model was more independent of sampling methods but linearily connected with sampling efficacy. A high non-linear correlation between factor and Shannon diversity was detected and a general function of this relationship developed and tested. The factor of the exponential species-area relationship may serve as an estimate of regional diversity.

3

On species-area relationships. 1, fit of power function and exponential model

Ulrich W.

Polish Journal of Ecology

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2000

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Vol. 48, nr 1

3-20

EN

A FORTRAN program is developed that generates model assemblages on the basis of three basic features of animal communities: the species-weight relationship, the density-weightrelationship, and the minimal density. Samplings from random placed individuals of such assemblages revealed the influence of the sampling method (sequential adding, nested and non-nested), the scale, and the underlying relative abundance distribution on resulting species-area relationships (SPARs). It is concluded that the type of the species-area relationship is not an intrinsic factor of an assemblage but depends especially on the sampling method and the unit of area. The fraction of species found only once in the sample (singletons) was the major factor influencing the model that fitted the SPAR best (at low fractions the exponential, at higher fractions the power function model). All sampling and structural factors that influence the fraction of singletons also influence the fit of the SPAR model. A mathematical derivation showed that at a certain fraction of singletons in the sample a shift from the power function to the exponential model is expected independent of assemblage type. This shift will occur between 20 and 30% singletons.

4

On species-area relationship. 3, The intercept of the power function and the exponential model

Ulrich W.

Polish Journal of Ecology

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2000

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Vol. 48, nr 1

37-48

EN

Using model assemblages the dependence of the intercept of the power function and the exponential model of species-area relationships on slope and factor value were studied. It is shown that the quotient of intercept and total species number in the assemblage (A[unit]/S[a]) can be interpreted as a relation between local and regional diversity and linked with species-area relations. Two general relations are derived and tested combining both concepts: z=a/ln[area] [...] with z being the slope of the power function model, H the Shannon diversity, Beta, Beta[1] and Beta[2] constants, and a the constant of the relation between S[unit]/S[a] and z. It is concluded that with the above functions species-area relationships can be used to infer the relation between local and regional species numbers and to compute regional diversities.