Plant Species Richness Vertical Pattern And The Test Of Rapoport's Elevation Rule On Mount Kenya,East Africa

The study of the vertical pattern of species richness along the elevation gradient is an important aspect in the study of biodiversity and conservation.Mount Kenya is the second highest peak in Africa and one of the most famous extinct volcanoes in East Africa.However,its research on species richness elevation pattern and the test of Rapoport's rule along the elevation gradient is still lacking.This study sought to explore the species richness elevation pattern of this Kenyan mountain's plants and examine the Rapoport's elevation rule for the detection of different plant components(including habits and geographical distribution)by the Steven's method.We first collected the required data from a variety of books and literatures on the distribution of plants in Mount Kenya,and also carried out the identification of specimens from the herbarium of the National Museum of Kenya,and finally obtained a list of the vascular plants in Mount Kenya.Various statistical tests were then performed such as regression analysis,boxplots,generalized additive models,and correlation tests using the R software.Our results showed that plant species richness along the elevation gradient showed a hump-shaped pattern with a peak richness at the mid-elevations.The annual mean temperature(AMT)was the most influential explanatory variable in the linear regression models,but the species richness was also strongly associated with area.The normalized differential vegetation index(NDVI)and the annual mean precipitation(AMP)were related less strongly with species richness.Although all the variables can explain the hump-shaped model,annual mean temperature,area,and annual mean precipitation best explain the unimodal pattern of species richness and the central elevation peak.At the mid-altitude,environmental conditions are appropriate,especially temperature and precipitation,thus allowing for the growth and survival of many different species.Conversely,at high altitudes,temperatures are too low,resulting in a decrease in species richness due to low physiological tolerance,while at the lower altitudes,species richness is relatively high compared to the higher altitudes due to the higher temperatures suitable for plant growth,coupled with the concept that species rich families inhabiting the lower elevations are regionally species rich.Although temperature is the most influential factor,all variable effects are interrelated in the formation of richness patterns.Our results quantify the effects of area,annual mean temperature,annual mean precipitation,and NDVI on plant species richness distribution patterns along the elevation gradient.In the research about species richness pattern and elevational Rapoport's rule(ERR)to test if the ERR is consistent among different life-forms and phytogeographic affinities,we recorded 1477 indigenous vascular plants from Mount Kenya including subspecies and varieties(157 families and 686 genera).Our results showed that species richness of the total species showed a positively skewed(hump-shaped)pattern along the elevation gradient and different life-forms and phytogeographic affinities showed similar hump-shaped patterns as the total species.The average elevation range size of the total species and herbaceous species showed increasing patterns along the elevation gradient,while lycophytes and ferns,and woody species showed an obvious downward trend after peaking in the high elevation regions.We concluded that the widely distributed herbaceous species which also have broad elevation range sizes are more applicable to ERR,while,the narrowly distributed woody species with small elevation range sizes occurring in the higher elevations could reverse ERR.Our results showed that the ERR is not consistent among different organisms in the same region.Therefore,the rule is not a consistently predictive pattern for comprehending species richness vertical patterns along the montane gradients.