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Species diversity Species diversity is diversity is the effective number of different species that are represented in a collection of individuals. Species diversity consists of two components, species richness and species evenness. evenness . Species richness is a simple count of species, whereas species evenness quantifies how equal the abundances abundances of of the species are. We use
D=
N (N-! " n (n-!
to calculate species diversity. #he hi$her the value calculated in an environment means the more stable it is. %t hence means the environment would more li&ely be able to withstand disturbance.
#rends in species diversity #he observed species diversity is affected not only by the number of individuals but also by the hetero$eneity of the sample. %f individuals are drawn from different habitats, habitats , the species diversity of the resultin$ set can be e'pected to be hi$her than if all individuals are drawn from a similar environment. %ncreasin$ the area sampled increases sampled increases observed species diversity both because more individuals $et included in the sample and because lar$e areas are environmentally environmentally more hetero$eneous hetero$eneous than small areas.
DIVERSITY WITHIN AND BETWEEN SE!ES #he diversity "ithin a "ithin a species is commonly called $enetic diversity and its important in a species health and resilience resilience cannot be understated. understated. #he more $enetically $enetically diverse a species is the more li&ely the species will survive disease and hardship. %n the case of diversity bet"een a species the overall community richness is what is sustained and protected. #he more diversity diversity between between species the more more stable the environment environment it belon$s belon$s too. #he relationship between species diversity and community stability hi$hli$hts the need to maintain the $reatest richness possible within biolo$ical communities. ndisturbed species-rich communities have the resilience to sustain a functionin$ ecosystem upon which life depends. #hese communities also are better able to absorb the effects of forei$n species.
!#$$%NITY AND E!#SYSTE$ STAB&ITY #he more diversity found within and between species result in $reater ecosystem and ecosystem stability. stability. #he stability stability of an ecosystem is the ability to remain remain the same same in face of a disturbance. disturbance. #he
ecosystem stability depends on the function or character of the ecosystem bein$ considered and the time scale over which it is bein$ considered. #he $reate $reaterr the stabil stability ity of the ecosyste ecosystem m the more resili resilient ent the the speci species es are are to disea disease se and and enviro environm nmen ental tal press pressure ure.. #he #he more more speci species es there there are are the more more li&ely li&ely some some will will be lost lost after after a disturbance. disturbance. )ence, diversity also decreases decreases ecosystem stability in terms of species retention. retention. N*#+ omple' and therefor therefor fra$ile communities are hence hence only found in stable environments. environments. When you want to retain ecosystem productivity after a disturbance, more species is better than less.
opulation Bi'tic i'ti c p'tenti p't ential al / p'p(lati'n is the the tota totall numb number er of all all the the or$a or$ani nism sms s of the the same same spec specie ies s who who live live in the the same $eo $eo$ra $raphic phical al are area a , and and have have the the capa capabi bili lity ty of inte interb rbre reed edin in$ $ . Bi'tic Bi'tic p'tentia p'tentiall is the ma'imum repro reproduct ductive ive capacity of a population under under optimum optimum environ environment mental al conditio conditions. ns. #his #his is usually restricted by environmental environmental resistance. %t is $enerally only reached when environmental conditions are very favourable. / species reachin$ its biotic potential would e'hibit e'ponential e'ponential population $rowth and be said to have a hi$h fertility fertility,, that is, how many offsprin$ are produced per mother.
'p(lati'ns occur in three main forms which includes linear, cubic and e'ponential as seen in the dia$ram below.
%n this study we will deal with e'ponential $rowth. E)p'nential p'p(lati'n *r'"th %n this type of $rowth an e'tremely rapid increase in the rate of population $rowth. 0ost populations have the potential to e'pand at an e'ponential rate, since reproduction is $enerally a multiplicative process. #wo of the most basic factors that affect the rate of population $rowth are the birth rate, rate, and the death rate. rate . #he intrinsic rate of increase is the birth rate minus the death rate. #wo modes of population $rowth #he +'ponential curve (also &nown as a 1-curve! occurs when there is no limit to population si2e.
#he 3o$istic curve (also &nown as an S-curve! shows the effect of a limitin$ factor (in this case the carryin$ capacity of the environment!.
Envir'nmental Resistance +nvironmental resistance are the conditions in the environment that prevent species population from $rowin$ $rowin$ out of control. control. %t is a mi'ture mi'ture of biotic and abiotic abiotic conditions conditions in the environme environment. nt. #hese #hese conditions includes a mi'ture of abiotic of abiotic factors such factors such as temperature temperature,, and biotic factors such factors such as natural enemies (biolo$ical control a$ents! a$ents! to limit the or$anism for e'pressin$ its full capacity to reproduce reproduce..
arryin$ capacity #he carryin* capacity of capacity of a biolo$ical species species in in an environment environment is is the ma'imum population si2e of the species that the environment environment can sustain sustain indefini indefinitely tely,, $iven $iven the food, food, habitat habitat,, water and and other neces necessit sities ies avail availab able le in the envir environm onmen ent. t. %t is simply simply defin defined ed as the envir environ onmen ment4s t4s ma'ima ma'imall load, which is different from the concept of population equilibrium. 5i$ure .6 below shows the carryin$ capacity of a population.
#he followin$ dia$ram shows three (7! population situations and the carryin$ capacities associated with it.