* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download ROLE OF KEYSTONE SPECIES IN AQUATIC ECOSYSTEM
Survey
Document related concepts
Biodiversity wikipedia , lookup
Unified neutral theory of biodiversity wikipedia , lookup
Occupancy–abundance relationship wikipedia , lookup
Restoration ecology wikipedia , lookup
Ecological fitting wikipedia , lookup
Introduced species wikipedia , lookup
Fauna of Africa wikipedia , lookup
Island restoration wikipedia , lookup
Theoretical ecology wikipedia , lookup
Habitat conservation wikipedia , lookup
Latitudinal gradients in species diversity wikipedia , lookup
Reconciliation ecology wikipedia , lookup
Transcript
ROLE OF KEYSTONE SPECIES IN AQUATIC ECOSYSTEM M.Feroz K h a n ’ , P re e th a P a n ik k a r ', A .P .S h a rm a *', B . C J h a ’ *a n d M .E .V ija ya ku m a r* " C e n t r a l I n l a n d F is h e r ie s R e s e a r c h I n s titu te ,B a r ra c k p o r e , H/es( B e n g a l - 7 0 0 1 2 0 " R e s e a r c h C e n t r e C IF R I, B a n g a lo r e - 5 6 0 0 8 9 Introduction “[Keystone sp ecie s] im p o rta n ce co n vin ce d m anagers and consen/ationists alike that the ecological im p a c t o f sin gle s p e c ie s matters. T h at is, in o rd er to m anage, understand, and re store e c o lo g ica l a s s e m b la g e s , th e roles o f individual species have to be understood and c o n s id e re d .” - Dr. R o b e rt Pain A keystone s p ecie s is a sp ecie s th a t has a d isproportionately large effect on its environment relative to its abu n da nce . S uch species play a critical role in maintaining the stru c tu re o f an e c o l o g i c a l c o m m u n i t y , a f f e c t in g m a n y o t h e r o r g a n is m s in an ecosystem and help in g to d e te rm in e th e typ e s and num bers o f various other species in the community. The role that a k e y s to n e s p e c ie s plays in its ecosystem is analogous to the role o f a keystone in an arch. W h ile th e k e ys to n e is u n d e r th e least p ressure o f any of the stones in an arch, the arch still c o lia p s e s w ith o u t it. Similarly, an e cosyste m may expenence a dramatic shift if a ke y s to n e s p ecie s is re m o ve d , even though th a t species was a small part of the ecosystem by m e a s u re s o f b io m a s s o r productivity. It has become a very popular concept in c o n s e rv a tio n biology. The keystone s p e c ie s co n c e p t w a s co ine d , in 1969. by the zoologist Robert T Paine, professor e m e ritu s o f the U n ive rsity o f W a sh ing to n, to explain the relationship between P is a s t e r o c h r a c e u s , a sp ecie s o f starfish, and M y tilu s californianus, a sp e a e s of mussel. In his classic 1966 paper. Dr. R o b e rt Paine descnbe sue a ^ klw ctnnp Bay in W ashington State, T h is led to his 1969 p ap e r w here he proposed the keystone species concept. T he c o n c e p t has been v e ry p opular in conservation, deployed in a range of contexts and m o b ilize d to e n g e n d e r su pp o rt fo r conservation. Given that the re are m a n y historical d e fin itio h s o f the keystohe speoies oohcept^ and without a c o n se n s u s on its e x a ct defin itio n, a list o f exam ple s best illustrates the concept of keystone species. A c la s s ic k e y s to n e s p e c ie s is a s m a ll p r e d a t o r t h a t p r e v e n t s a particular herbivorous species from elim inating d o m in a n t plant species. Since the prey numbers are low, the keystone pre da tor num bers can be even lower and still be effective. Yet without the predators, the herbivorous prey w o u ld e xplode in num bers, w ipe out the dominant plants, and dramatically alter the character o f the ecosystem. T he exact scenario changes in each example, but the central idea rem ains that through a chain o f interactions, a non-abundant species has an out-sized im p a ct on e cosyste m functions. As was described by Dr. Robert Paine in his classic 1966 paper, some sea stars may prey on sea urchins, mussels, and oth e r shellfish th a t have no other natural predators. If the sea s ta r is re m o ve d fro m th e e c o s y s te m , th e m u s s e l p o p u la tio n explodes uncontrollably, driving out most o th e r species, w h ile th e urchin population annihilates coral reefs. Similarly, sea otters protect kelp forests fro m d a m a g e by sea urchins. Kelp “roots’', called holdfasts, are merely anchors, and not the va s t nutrient gathering networks of land plants. Thus the sea urchins only need to eat th e ro o ts o f th e kelp, a tiny fraction o f the plant's biomass, to remove it fro m the ecosystem . T h e s e creatures need not be apex predators. Sea stars are prey fo r sharks, rays, and se a a nem ones. S ea otters are prey for Orca. T he c o n c e p t The term keystone species has enjoyed an e n d u rin g popularity in th e ecological literature since its introduction by Robert T. P aine in 1969: Paine (1969) w as cited in more than 92 publications fro m 1970 to 1989; an e a rlie r p ap e r (P aine 1966), which introduced the phenomenon o f keystone specie:- in intertidal system s but did not use the term, was cited more than 850 tim es during the sa m e period. Paine (1966, 1969) noted th a t e x p e rim e n ta l re m o v a l o f so m e ro c k y intertidal carnivores (such as the starfish P is a s te r) led to n early co m p le te d o m in a n ce o f the substrate by one or two sessile species (mussels), resulting in greatly decrea sed species diversity. In this and other cases, the im portance o f the k e y sto n e p re d a to r derived from two requisites (Paine 1969, P im m 1980): the p re d a to r preferentially ate and controlled the density of a primary consumer, and the co nsu m e r w as ca pable o f e xcluding (through competition or predation) other species from the com m unity. Essentially, then, the early connotation was that keystone predators are im portant because they control the densities of important com petitor or predator species. P redators have also been labeled keystone when they control the densities o f o th e r types o f e c olo g ica lly significant p re y species. For example, sea otters {E n h y d ra lutn's) have often been referred to as keystone predators (e.g., Duggins 1980, E s te s a n d P a lm is a n o 1 9 7 4 ) b e c a u s e t h e y lim it d e n s it y o f s e a u rc h in s {S tro n g y lo c e n tro tu s s p p ^ . which in turn eat kelp and o th e r fle shy m a cro alga e th a t form the basis of a different co m m u nity than is p resent in th e ir a bsence (V anB laricom and Ml Estes 1988). Thus, o tte r re m o va l has com m u nity-le vel influences, by releasing from predation a primary c o n s u m e r th a t eats a plant th a t harbors o th e r organisms. As used by Paine and o th e r ecologists, the re are two hallmarks o f keystone species. First, their presence is cru cia l in m a in tain in g the organization and diversity o f their ecological communities. S eco n d, it is im plicit that these species are exceptional, relative to the rest of the com m unity, in th e ir im p o rtan ce . Given the assum ed importance of keystone species, it is not surprising th a t biolog ists have advocated th a t key or keystone species be special ta rg e ts in th e efforts to m a xim ize biodiversity protection (e.g., Burkey 1989, Frankel and Soule 1981, Soule and S im berloff 1986. Terborgh 1986) and as species in need of priority p ro te ctio n (e.g , Cox e t al. 1991). The keystone s p e c ie s play a central a nd critical role in m ain ten an ce of com m unity structure and ecosystem functio ning . If an e c o s y s te m can be returned to a state in which the keystone species flo un sh , the n all the o th e r species, which d ep e nd on them, will also flourish. The im p o r ta n c e o f b io d iv e r s it y in e n v ir o n m e n ta l m a n a g e m e n t b e s id e socioeconomic deve lo pm en t and well being o f hum an society, has led to the development of various techniques fo r c o n se rva tio n o f e co lo g ic a l diversity. S om e simple w a ys of managing the natural s ys te m s should be evolved so as to retain and conserve the identity of a region for a better to m o rro w . O n e o f th e sim p le st w a ys o f doing so is by identifying species, which play the key role o f h old in g to g e th e r the entire biological com m unity or ecosystem. These sp ecie s a re know n as 'k e y s to n e species in ecological term. The central core o f k e y s to n e ,c o n c e p t is th a t only a fe w species have uniquely important effect on th e c o m m u n ity o r e c o s y s te m by virtue o f th e ir uniquely important traits and attributes. O nly th o s e s p ecie s can be considered as keystone species that had a significant e ffect on ‘tim e w in d o w ’ o f o th e r species. In m o s t o f the cases, it is indeed groups of sp ecie s ra th e r th a n individual species th a t a ssum e im portance and these species groups could be referred to as th e ‘keystone g ro u p s ’ o r ‘functional groups . Keystone species or 'k e y s to n e species g ro u p s ' play a vital role in m aintaining ecosys em and regulating the biodiversity. Loss o f vital fu n c tio n , and ch an g es within the ecosystem or community would fo llo w if su c h s p ecie s g ro u p s are rem oved fro m the system. These species are Responsible' fo r th e e x isten ce o f an ecosystem o f certain type and create possibilities for the d e v e lo p m e n t o f o th e r ty p e s o f com m unities. Biodiversity w ithin an are a can be ch a ra c te rize d by m e a s u r e s o f species richness species diversity, ta x ic diversity, and fu n c tio n a l diversity, e ach highlighting d fferen perspectives Functional diversity refers to th e varieties o f functions earned hy d fle re n species and groups o f sp e c ie s know n as fu n c tio n a l groups T he population ^ V ^ c s o keystone species define the pattern o f su ccessio n “ egetatio n ^T u rno ve rcyd es of and energy flows in an e c o s y s te m are d o m in a te d by the life ac ivity o f l < 7 = ^ ® and these activities d e te rm in e th e m a jo r s h ifts in ecosystem ‘ ‘ h® tenporal scales P op u latio n m o sa ics o f ke y s to n e species have dimensions, and pop u latio n m o sa ics o f su b o rd in a te species are th e re b y determined by the keystone species. K eysto ne sp ecie s are re s p o n s ib le fo r th e e xiste n ce o f the ecosystem and maintenance o f its species diversity. S o the biodiversity in any ecosystem can be manipulated by perturbations in such u niq u ely im p o rtan t species. A m a jo r research ch allen g e fo r e c o lo g is ts is to p re d ic t w h ic h s p e cie s in the community would become keystone species. The current level o f conceptual u nd e rsta n d in g o f th e effe cts o f biodiversity on ecosystem processes is so prim itive that at this sta g e it is possible to recognize the linkages at the level of functional g ro up s only. In a n y e c o s y s te m the re are diverse types of functions performed by different species or sp ecie s g roups. However, no tw o species or individuals are identical. It m a y be noted that sp ecie s diversity within the functional groups or genetic diversity within the species has im p o rta n t ecosystem consequences. Although certain species have much g re ate r in flue n ce than others on an ecosystem structure, not all ecosystems include the sam e species th a t exert such pervasive influence on them. In fact most ecosystem s are so m e w ha t se nsitive to the loss o f a fe w species, though som e losses have g re a te r im pact on th e system than others. Nevertheless, identification of such species, w hich w ould function a s keystone species in an ecosystem can help in the conservation o f that ecosystem . T h e fa c t th a t so m e species m atter more than the others, becomes especially clear in the ca se o f ‘keystone sp ecie s’ or ‘ecosystem engineers’ or ‘organism s with high im portance va lu e fo r th e c o m m u n ity ’. These terms may differ in usage, but all re fer to those sp ecie s w h o s e loss o r rem oval results in disproportionately greater im pact on the com m u nity w h e n c o m p are d to th e loss o f other species. M em bers o f the functional g ro up s m aintain and d ete rm in e th e resilience o f the ecosystem by spreading a wide ra n ge o f ecological niche s exploited by th e component species. The contribution of individual species tow ard e c o s yste m d e ve lo p m e n t varies in time and space, and accordingly, not all species are e q u a lly im p o rta n t w h e n w e look at the community stability and functioning. T he co m m u n ity fu n c tio n m ay be m aintained by a species or sum m ed effects o f a fe w species. S o m e s p e c ie s und o ub ted ly play more significant role than others in ecosystem function. T he varieties o f functions that a species can perform are limited and consequently, an increase in species richness also increases functional diversity, producing an increase in e colo g ica l stability. W ithin a com m unity it is not possible to su bstitu te s p ecie s fo r one another, rather there are a good num ber o f co m b ina tio ns o f sp ecie s th a t ca n produce sim ila r ecological roles. There is no intrinsically unique level at w h ich biotic diversity affects ecosystem processes. Based upon their e colo g ica l roles and th e sp ecific ecological niches that they exploit, species can be divided into 'functional groups'. A fu n c tio n a l g ro up refers to a group of species, which perform ecologically sim ila r roles in ecosystem processes. For heuristic purposes, the u sages o f keystone species is divided into five types. This categorization is not m eant to im ply m utually exclusive g ro up s or an exhaustive review of the term s application, but rather to show the diversity of keystone effects referred to in the literature Table 1. C a te g o rie s o f p re s u m e d k e ysto n es and the effects of th e ir e ffe c tiv e re m o va l fro m a system. K eystone category E f fe c t o f re m o v a l Predator In cre a se in one o r se veral p re da tors/ consum ers/com petitors, w h ich s u b s e q u e n tly e x tirp a te s several p re y/co m p e tito r species Prey O th e r sp e c ie s m o re se n s itive to predation m ay becom e extinct; p re d a to r p o p u la tio n s m a y crash Plant Extirpation o f d e p e nd en t anim als, potentially including pollinators and se e d d is p e rse rs Link F ailure o f re p ro d u c tio n and recru itm e nt in certain plants, with p ote ntia l s u b s e q u e n t lo sses Modifier Loss o f stru c tu re s /m a te ria ls th a t a ffect h abitat type and energy Determining th e K e y s to n e S t a t u s o f S p e c ie s All species are im p o rta n t fo r th e e xisten ce o f an ecosystem and fo r the m aintenance of its various functions, b u t as m e n tio n e d earlier, all are not equally important. The identification of species a nd g ro u p s o f sp ecie s, w h ich play key role in maintaining the ecosystem stability a nd re s ilie n c e by in flu e n c in g th e s tru c tu re and fun ctio n o f an ecosystem is a stup e nd o us task, and very fe w atte m p ts have been m a d e in this direction. Since the importance o f s o m e sp ecie s m a y la rg ely be th e co n se q u e n ce of their rich interaction structure, o ne p ossib le q u a n tita tive a p p ro ach to identify the most influential species is to study th e ir p ositio n in the n e tw o rk o f interspecific interactions. We have developed a n e tw o rk s tru c tu re o f th e reservoir e cosyste m is built using Ecopath with Ecosim s o ftw a re fo r c h a ra c te riz in g th e in teraction structures o f each species. This study w a s co n d u c te d at K a ra p u z h a reservoir, located at W ayanad Distnc of Kerala In this p ap e r th e ke y s to n e n e s s o f th e functional g ro up s (species or gro up of species) of food w eb m o d e l o f a re se rvo ir e c o s y s te m is exam ined. T he species in t^his reservoir are assem bled into 15 fun ctio na l g ro u p s fro m D etritus to A qu a tic birds. The total system throughput in th e re s e rvo ir is 3 0 0 3 9 t/km 2 with a connectance index of 0.277 The system o m n io v o ry in dex is e s tim a te d a t 0.109. T he sum o f all detritus flows into detntus is 11268.45 t/km 2 . T h e a n a ly s is o f th e mixed tro p h ic impacts presented allows ranking o f fun ctio na l g ro u p s by th e ir ke ysto n en e ss. T he keystone in ex from 0.610 for P hyto plan kton to 2.839 fo r a q u a tic birds. T he im p o rtan t result is that keystone species exert th e ir high im pact by m e a n s o f top-dow n effects, a feature initially S'jggested being a defin in g c h a ra c te n s tic o f k e y sto n e species. C la n a s g a n e p in u s has a very high key stone index at 2.168 which show s h o w m u ch influence an invasive species has on the food web o f this rese rvoir e cosystem . T h e study sh ow s th a t lower biomass species in this reservoir ecosystem are show ing v e ry high ke ysto n e indices. Fig. Keystone indices o f K ara p u z h a R e se rvo ir ecosystem . ‘he Key Stone Species at Reservoir Aquatic Bird 2.8|9 t 0 Crustaceans M E I Major carps ® I.34 fi Minor cdr Minno „ 1,371 Barbs 1,319 l. ljl 1 African catfish « 2.168 Eels 2.444 keheads D plankton 0.159 'h O.mossamblcus'h, J \ ^ 0 978 ^''''’’t o ^ l a n k t o n 0.1 ' ‘W 469 0.2 0.3 0.530 0.4 0.5 0,6 0.7 0.8 0.9 1.0 Relative Total C on clu sio n n a t u r a lT v s t e m r w r t h m hers7 ecoloqicai functioninn nf ml ConL':vr;“ f '^ ^ com p lexity o f interactions in oause the loss of species tinat are so im portant in determ ining the rs,,;,; : ten^r^'^mofomr^ ecosystems or processes If o u r nn;=??rtn b e tw e e n pro te ctin g species, areas, a reliable supply of ecosystem serw'ces th e n ^ r iP ^ r ^ ^ e co s ys te m structure and maintain will be the only real long-term s o lu tio n ’fn r consenting im portant species only the rarest sp e c e s is only a sym ptom atic S m e n f p ^ ' * ^ loss u ltim a tely protecting inspire theoreticians to e x o L p thp . x ® tantalizing results should weakly interacting specres a^d o n l ? a s s e m b la g e s stru cture d with many useful^'in d em on sir U g h a r u n d e 'o e rt strong interaotors.. The co ncept has been _conditions so m e species have particularly strong interactions, a nd w e recognize th a t in recom m ending tiie abandonm ent o f a popular and e vocative co n ce p t the re is a d a n g e r of making it more . For fu r th e r re a d in g . 1. Paine, R.T. (1 9 9 5 ). “A C o n v e rs a tio n on R e fining th e C o n c e p t o f K eysto ne S p e c ie s ” . C o n s e r v a t io n B io lo g y 9 (4 ): 9 6 2 - 9 6 4 . d o i: 1 0 . 1 0 4 6 / j . 1 5 2 3 1739.1995,09040962.x. 2. Mills. L.S.; Soule, M.E.; Doak, D.F. (1993). "The K eystone-Species Concept in Ecology and C o nse rva tio n", B io S cie n ce(B ioS cie nce , Vol. 43, No. 4) 43 (4): 2 1 9 224.doi:10.2307/1312122. JS T O R 1312122, 3. “Keystone S pecies Hypothesis". U nive rsity o f W ashington. Retrieved 2011-02-03. 4. Stolzenberg, W illia m (2008). W h e re the W ild Things W ere: Life, death and ecological wreckage in a,land o f vanishing predators. B loom sbury USA. ISBN 1-59691-299-5. 5. Paine, R.T. (1966). "F oo d W e b C o m p le x ity and Species Diversity". The Am erican Naturalist 100 (910): 6 5-7 5 .d o i:1 0 .1 0 8 6 /2 8 2 4 0 0 . JS TO R 2459379. 6. Paine, R.T. (1969). “A N ote on T ro p h ic C o m p le xity and C o m m u n ity Stability” . The American N aturalist 103 (929): 9 1 - 9 3 . d o i:1 0 .1086/282586. JS T O R 2459472. 7. Barua, M. (2011) M obilizing m e tap h ors; th e p opular use o f keystone, flagship and umbrella species c o nce p ts. B io dive rsity and Conservation, 20: 1427-1440. 8. Robert D. Davie (2003). "Linking K e y sto n e Species and Functional Groups: A New Operational D efinition o f the K e ysto ne Species C o n ce p t” . Conservation Ecology. Retneved 2011-02-03. 9. Creed Jr, R.P. (2000). “ Is the re a n e w k e ysto n e species in North Am erican lakes and rivers?". O IK O S 91 ( 2 ): 4 05 .doi:10.1034/j. 1600-0706.2000.910222.x. 10. Estes, James E.; N o rm a n S. Smith, Jo hn F. P a lm isa n o (1 9 7 8 ). "Sea otter predation and c o m m u n i t y o rg a n iz a tio n in t h e W e s te rn A le u t ia n Is la n d s , A la s k a ” . E c o lo g y ( E c o lo g y , V o l . '5 9 , N o. 4) 5 9 (4 ): 8 2 2 - 8 3 3 . d o i.1 0 .2 3 0 7 / 1938786. JS T O R 1938786. 11. Cohn, J.P (1998). "U n d e rs ta n d in g S ea O tte rs ” . BioScience(BioS cience, Vol. 48, No. 3) 48 (3): 1 5 1 -1 5 5 .d o i: 1 0 .2 3 0 7 /1 3 13 2 59 . JS TO R 1313259. 12. Estes, J.A ; Tinker, M.T.; W illiam s, T M .; Doak, D.F, (1998-10-16). “Killer whale pred ation on sea otters linking oceanic and nearshore ecosystem s . Science 282 (5388). 4 7 3 - 4 7 6. B I b c o d e 1 9 9 8 S 0 i . . . 2 8 2 . . 4 7 3 E . d o i : 1 0 . 1 1 2 6 / science.282.5388.473.PM ID 9774274. 13 Nowell K and Jackson, P. (com pilers and editors) 1996. W ild Cats, Status Survey and Conservation Action Plan, lU C N /S S C C at S pecialist Group. iU C N , Gland, Switzerland, (see Panthera Onca, pp 1 18 -1 22 ) 14. Lambeck, Robert J. (1999). Landscape Planning fo r Biodiversity C onservation in A gricultural Regions: A C ase Study fro m th e W h e a tb e lt o f W e s te rn Australia. Biodiversity Technical P aper No. 2. C S iR O D ivision o f W ildlife and Ecology- 15. W alker, B rian (1995). "C o n s e rv in g B io lo g ic a l D iv e rs ity th r o u g h E c o s ys te m R e s ilie n c e ” . C o n s e r v a t io n B io lo g y 9 (4 ): 7 4 7 - 7 5 2 . d o i: 1 0 . 1 0 4 6 / j. 1 5 2 3 1739.1995.09040747.x. 16. Caro, T. (2010) Conservation by Proxy, island Press, W a sh ing to n DC. 17. Reichman, Tom. "Salmon nutrients, nitrogen isotopes and coastal fo re s t” . Salmon nutrients, nitrogen isotopes and coastal forest. University o f V ictoria. R etrieved 3 June 2011. 18. Nebraska Gam e and Park Com m ission: the Prairie Dog. 19. Prairie Dog Coalition -A s s o c ia te d Species 20. Wright, J.R; Jones, C.G.; Flecker, A.S. (2002). "An ecosystem engineer, the beaver, increases species rich n ess at the la n d s c a p e sca le ". O e c o lo g ia 132 (1): 9 6 101 .doi: 10.1007/S00442-002-0929-1. Retrieved 2007-10-04. 21. Leakey, Richard; Roger Lewin (1999) [1995]. "11 T he m odern e le p h a n t story". The sixth extinction: biodiversity and its survival, London: Phoenix, pp. 2 1 6 -2 1 7 . ISBN 185799-473-