Influence of temperature on the reproductive potential of

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Eq. (I) will always be higher than life table values, because juvenile mortality is not included in the former. This could be remedied by calculating r = I/D in pdN e ...
MARINE BIOLOGY

Marine Biology 45, 255-260 (1978)

9 by Springer-Verlag 1978

Influence of Temperature on the Reproductive Potential of Oncholaimus oxyuris (Nematoda: Oncholaimidae) C. Heip, N. Smol and V. Absillis Department of Zoology, State University of Gent; Gent, Belgium

Abstract

The large n e m a t o d e O n c h o ! a i m u s oxyuris D i t l e v s e n , 1911 is a d o m i n a n t p r e d a t o r in a s h a l l o w p o l y h a l i n e b r a c k i s h - w a t e r p o n d in B e l g i u m . The r e p r o d u c t i v e p o t e n t i a l of this s p e c i e s w a s c a l c u l a t e d as the i n t r i n s i c r a t e of n a t u r a l i n c r e a s e r = I / D in PNe, in w h i c h D is the g e n e r a t i o n time, p is the p e r c e n t a g e of females, and N e is the n u m b e r of eggs per female. The g e n e r a t i o n time v a r i e s b e t w e e n 570 days at 5oc and 101 days at 25oc and is the m a i n f a c t o r in the d e t e r m i n a t i o n of r. The relat i o n s h i p b e t w e e n r and t e m p e r a t u r e is n e a r l y linear and is g i v e n by r = 0 . 0 0 1 3 T 0.0042. The r e p r o d u c t i v e p o t e n t i a l of o. o x y u r i s is m u c h lower than w o u l d be pred i c t e d f r o m b o d y size; this, and the d o m i n a n c e of m a l e s in the p o p u l a t i o n , is disc u s s e d in the l i g h t of the e v o l u t i o n of s t a b l e p r e d a t o r - p r e y systems. - -

Introdueion

F r e e - l i v i n g n e m a t o d e s are the m o s t n u m e r ous m e t a z o a n s in the m a r i n e b e n t h o s and even t h e i r i m p a c t on the p l a n k t o n m u s t be i m p o r t a n t , at l e a s t in the s h a l l o w w a ters a b o v e the c o n t i n e n t a l shelves, as they p l a y a r o l e in n u t r i e n t r e g e n e r a tion and the a v a i l a b i l i t y of d e t r i t u s to h i g h e r levels in the food c h a i n (Tenore e t al., 1977). Yet, little is k n o w n a b o u t the d y n a m i c s of m a r i n e n e m a t o d e p o p u l a tions and only few a u t h o r s h a v e c a l c u lated t h e i r r e p r o d u c t i v e p o t e n t i a l or their t u r n o v e r . In this study, we c h o o s e to i n v e s t i gate the i n f l u e n c e of t e m p e r a t u r e on the r e p r o d u c t i v e p o t e n t i a l of the large species O n c h o l a i m u s oxyuris D i t l e v s e n , 1911, m a i n l y for two r e a s o n s : firstly, m o s t s t u d i e s till n o w h a v e b e e n m a d e on small, r a p i d l y r e p r o d u c i n g s p e c i e s , and s e c o n d ly, this s p e c i e s is an i m p o r t a n t p r e d a tot, y e t at times it may b e c o m e the d o m i nant s p e c i e s in the c o m m u n i t y w h e r e we s t u d i e d it, p o s i n q some i n t e r e s t i n g p r o b lems on the r e s i l i e n c e of this c o m m u n i t y . The r e p r o d u c t i v e p o t e n t i a l can be c h a r a c t e r i z e d by the i n t r i n s i c rate of n a t u r a l i n c r e a s e , r, in the e q u a t i o n of an e x p o n e n t i a l l y i n c r e a s i n g p o p u l a t i o n w i t h o u t m o r t a l i t y , N t = N o e r t ; or in a life table as the s o l u t i o n of the equation I = ~ ~ r x i x m x " in w h i c h i x is the p r o p o r t i o n of f e m a l e s s u r v i v i n g u n t i l

age x, and m x is the n u m b e r of f e m a l e p r o g e n y per f e m a l e of age x. W h e n m repr e s e n t s the g e n e r a t i o n time, r = I / m i n R o , in w h i c h R o is the n e t r e p r o d u c t i v e rate, e q u a l to N D / N o for our p u r p o s e or to ~ I x m x in life t a b l e n o t a t i o n . W h e n p is the p e r c e n t a g e of f e m a l e s in the p o p u l a tion and N e the n u m b e r of eggs per female, N O / N o = p N e , f r o m w h i c h r

=

I/D

in p N e .

(I)

May (1976) s h o w e d that r as c a l c u l a t e d by Eq. (I) is a g o o d a p p r o x i m a t i o n of r as c a l c u l a t e d f r o m a life t a b l e in the case of m a n y a r t h r o p o d s , and C a u g h l e y and B i r d (1971) p r o p o s e d the (overrestrictive) c o n d i t i o n r