ATOLL RESEARCH BULLETIN NO. 306
EFFECTS OF FERAL GOATS (CAPRA HIRCUS) ON ALDABRA ATOLL BY
BRUCE E. COBLENTZ AND DIRK VAN VUREN
ISSUED BY
NATIONAL MUSEUM OF NATURAL HISTORY SMITHSONIAN INSTITUTION
WASHINGTON, D.C., U.S.A.
October
1987INDEX MAP OF ALDABRA ATOLL
(after D.R. Stoddart and C.A. Wright, 1967, Nature V. 2 13 No. 50821
i CAMP
PASSE HOUREAU ANSE GRAND
GRABEAU MIDDLE
SETTLEMENT
TRIP CAIRN ClNQ CASES
- .-- -
ANSE TAKAMAKA M A N G R O V E
DUNE 5 Miles I
C H A M P I G N O N ( d i s s e c t e d Ilmestone) P L A T I N ( f l a t limestone)
EFFECTS OF FERAL GOATS (CAPRA HIRCUS) ON ALDABRA ATOLL BY
BRUCE E. COBLENTZ~ AND DIRK VAN VUREN~
The o r i g i n s of goats on o c e a n i c i s l a n d s a r e d i v e r s e and o f t e n p o o r l y documented. F o r most p o p u l a t i o n s , t h e d a t e and purpose o f i n t r o d u c t i on remai ns u n c e r t a i n ( r e v i ewed by Cob1 e n t z 1978), and i n any event, p a l e s by compari son w i t h t h e e c o l o g i c a l consequences.
The e a r l i e s t documented i n t r o d u c t i o n of goats t o an o c e a n i c i s l a n d was p r o b a b l y t h a t o n t o St. Helena where t h e i n i t i a1 i n t r o d u c t i o n
o c c u r r e d e i t h e r i n 1502 ( D a r w i n 1860) o r 1513 (Wallace 1911). The e x t e n s i v e damage t o n a t i v e v e g e t a t i o n r e s u l t e d i n an o r d e r , i s s u e d i n 1731, t h a t a l l s t r a y a n i m a l s s h o u l d be d e s t r o y e d (Darwin 1860).
N e v e r t h e l e s s , by 1810 t h e i s l a n d was reduced f r o m a h e a v i l y f o r e s t e d c o n d i t i o n t o an o c e a n i c rock (Darwin 1860, Wodzicki 1950). An
i m p o r t a n t p o i n t c o n c e r n i n g t h e d e s t r u c t i o n of t h e endemi c f o r e s t s o f S t . Helena was t h a t i t t o o k a l i t t l e o v e r 200 y e a r s f o r t h e
d e s t r u c t i o n t o be completed (Darwin 1860). When t h e l a s t o f t h e mature t r e e s f e l l , t h e seed sources were gone f o r e v e r . I n c o n t r a s t , g o a t s have o n l y been p r e s e n t on A l d a b r a f o r a l i t t l e more t h a n 100 y e a r s ( S t o d d a r t 1981).
P u b l i s h e d d e s c r i p t i o n s o f t h e e f f e c t s of f e r a l goats i n i n s u l a r ecosystems have been n e a r l y u n i versa1 l y n e g a t i v e , o f t e n d r a m a t i c a l l y s o ( r e v i e w e d by C o b l e n t z 1978), i n c l u d i ng d e s t r u c t i o n of n a t i v e v e g e t a t i o n , e x t i n c t i o n o f p r e f e r r e d f o r a g e species, p r e v e n t i o n o f s e e d l i n g r e g e n e r a t i o n , a c c e l e r a t e d s o i l e r o s i o n , and numerous i n d i r e c t e f f e c t s upon endemic fauna, up t o and i n c l u d i n g e x t i n c t i o n ( f o r
example, Greenway 1958).
1 Department o f F i s h e r i e s and W i l d l i f e , Oregon S t a t e U n i v e r s i t y , C o r v a l l i s , OR 97331-3803, U.S.A.
2 Department of S y s t e m a t i c s and Ecology, Uni v e r s i t y of Kansas, Lawrence, Kansas 66045, U.S.A.
Coblentz & Van Vuren
Because o f i t s f i n a l i t y , e x t i n c t i o n seems t o t a k e precedence i n t h e manner i n which we view t h e e f f e c t s o f f e r a l goats; however, i t i s t o t h o s e i n s u l a r species threatened, b u t n o t y e t e x t i n c t t h a t ' a t t e n t i on needs t o be d i r e c t e d . Although a r e l a t i v e l y few i s l a n d species have been d r i v e n t o e x t i n c t i o n by f e r a l goats ( b u t see Thorne 1967),
p r o b a b l y a g r e a t many more have a p r e c a r i o u s s t a t u s t h a t i s o f t e n t i m e s unnoticed. High l e v e l s of g r a z i n g pressure, i n a d d i t i o n t o n e g a t i v e e f f e c t s on f a v o r e d p l a n t species, may have d r a m a t i c e f f e c t s upon i n v e r t e b r a t e communities (Hutchinson and K i n g 1980) ; t h e e f f e c t s o f f e r a l sheep have been shown t o produce marked e f f e c t s upon i n s u l a r a v i f a u n a l communities (Van Vuren and Coblentz 1987).
GOATS ON ALDABRA
-
BACKGROUNDGoats have been p r e s e n t on Aldabra (46'20' E. Long., 9'24' S. Lat.) s i n c e sometime p r i o r t o 1878 (Stoddard 1981); however, i t i s o n l y i n r e c e n t y e a r s t h a t t h e i r presence has been viewed w i t h alarm, and t h e n o n l y by some o f t h e b i o l o g i s t s v i s i t i n g t h e At01 1. A l t h o u g h t h e r e i s u n c e r t a i n t y about goat numbers on t h e At01 1 d u r i n g t h e p a s t 100 years, t h e y a p p a r e n t l y have n o t achieved t h e s p e c t a c u l a r l y h i gh d e n s i t i e s on Aldabra as t h e y have on o t h e r , more p r o d u c t i v e oceanic i s l a n d s . However, Dupont (1929, c i t e d i n S t o d d a r t 1981) mentioned
"hundreds o f them" i n 1916 and " s e v e r a l thousands" by August 1929.
Goat numbers on Aldabra appear t o have been r e l a t i v e l y low i n t h e p a s t s e v e r a l decades ( S t o d d a r t 1971, Goul d and S w i n g l and 1980) except t h a t t h e y have i n c r e a s e d markedly on Grande Terre, t h e l a r g e s t i s l a n d o f t h e A t o l l , i n t h e p a s t s e v e r a l years. T o t a l goat numbers on
Aldabra i n c r e a s e d f r o m an e s t i m a t e d 500-600 i n d i v i d u a l s i n 1976-77 (Gould and Swingland 1980) t o as many as n e a r l y 1300 (Gould-Burke, M.
1986, paper g i ven a t I n t e r n a t i o n a l A1 dabra Workshop, Smi t h s o n i an I n s t i t u t i o n ) i n 1985. The i n c r e a s e i n goat numbers prompted concern f r o m s e v e r a l b i o l o g i s t t h a t some elements o f t h e endemic Aldabra b i o t a would be s e v e r e l y impacted by h i g h l e v e l s o f h e r b i v o r y imposed by t h e goats.
Our p r o j e c t was p r e c i p i t a t e d i n d i r e c t l y by t h e r e p o r t o f Newing e t a l . (1984) i n which d a t a were p r e s e n t e d i n d i c a t i n g t h a t goats were g r e a t l y i n c r e a s i n g on b o t h I l e Malabar and Grande Terre, and t h a t on Ma1 abar goats were s p r e a d i n g westward i n t o p r e v i o u s l y unoccupied areas which were t h e s o l e h a b i t a t of t h e endangered Aldabran brush w a r b l e r ( N e s i l l a s aldabranus). I n a d d i t i o n , a l t h o u g h t h e r e were f a r more qoats on Grande T e r r e t h a n on Malabar. few r e s e a r c h e r s o t h e r t h a n
~ e w i n g e t a l . (1984) f e l t t h a t t h e r e was any s i g n i f i c a n t c o m p e t i t i o n between t h e endemi c g i a n t t o r t o i se (Geochelone g i gantea) and t h e goats, a l t h o u g h t h i s b e l i e f seems t o have been based p r i m a r i l y upon comparison o f f o o d h a b i t s ( f o r example, Gould and Swingland 1980).
Thus, o u r p r o j e c t was i n s t i t u t e d as a p i l o t p r o j e c t . Our o b j e c t i v e s were t o 1 ) e r a d i c a t e , i f p o s s i b l e , a l l goats from I l e Malabar, 2) d e t e r m i n e i f e r a d i c a t i o n o f goats was p o s s i b l e from t h e e n t i r e At01 1, and 3 ) determine s u b j e c t i v e l y t h e e f f e c t s o f goats on m a j o r p o r t i o n s of t h e Aldabran b i o t a . The r e s u l t s o f o b j e c t i v e s 1 and 2 a r e r e p o r t e d elsewhere (Coblentz and Van Vuren, 1987 u n p u b l i s h e d r e p o r t t o Seychel 1 es, I s 1 ands F o u n d a t i o n ) ; t h i s paper r e p o r t s o u r f i n d i n g s concerning o b j e c t i v e 3.
C o b l e n t z & Van Vuren
EFFECTS OF GOATS ON ALDABRA
We were on A l d a b r a 30 January t h r o u g h 8 March 1987. On I l e Malabar, a l l a c c e s s i b l e areas between Passe Houreau and a p o i n t about 0.5 km west o f Anse Grand Grabeau were searched f o r goats and goat s i g n . Goats were shot whenever observed, and areas h a v i n g s i g n o r where goats were heard b u t n o t seen were searched r e p e a t e d l y u n t i l
i n d i v i d u a l s were l o c a t e d and k i 1 le d . S u b j e c t i v e e v a l u a t i o n s o f goat i m p a c t s were made c o n t i n u o u s l y as areas were searched f o r goats and s i g n . On Grande T e r r e , a l l h a b i t a t s i n an area between t h e lagoon a t Bras C i n q Cases and t h e c o a s t l i n e f r o m r o u g h l y 1 km n o r t h o f t h e a i r s t r i p c a i r n , south and southwest n e a r l y t o Anse Takamaka, were searched f o r goats and examined f o r t h e i r e f f e c t s .
Environmental damage due t o goats on I l e Malabar was judged t o be l i g h t . S i g n i f i c a n t e f f e c t s o f goats, p r i m a r i l y as browse l i n e s on p r e f e r r e d f o r a g e species, were observed i n o n l y a few l o c a l i z e d areas.
The h e a v i e s t goat damage, and t h e l a r g e s t area o f c o n t i g u o u s
goat h a b i t a t , was i n t h e M i d d l e Camp area, and much o f i t p r o b a b l y o r i g i n a t e d i n p a s t y e a r s when t h e p o p u l a t i o n was h i g h e r (>76 i n 1976-77, Gould-Burke, M., 1986, paper g i v e n a t I n t e r n a t i o n a l A l d a b r a Conference, Smithsonian I n s t i t u t i o n , vs 32 i n t h i s s t u d y ) . However, even a t M i d d l e Camp t h e r e were many shrubs a v a i l a b l e t o t o r t o i s e s , and t o r t o i s e s were f r e q u e n t l y observed browsing.
F e r a l goats a r e s e v e r e l y damaging t h e Grande T e r r e ecosystem; t h a t was i m m e d i a t e l y e v i d e n t t o us as we began h i k i n g i n l a n d f r o m Bras C i n q Cases on t h e lagoon s i d e o f t h e i s l a n d . We n o t i c e d t h a t goat s i g n was abundant w e l l i n t o t h e mangroves ( f r o m t h e l a n d s i d e ) , and t h a t a v i r t u a l l y c o n t i n u o u s browse l i n e n e a r l y 2 m i n h e i g h t was p r e s e n t . Even a c o n s i d e r a b l e amount o f Pemphis a c i d u l a had been c o m p l e t e l y browsed t o t h i s h e i g h t , and numerous i n d i v i d u a l s had been k i 1 le d .
Perhaps t h e g r e a t e s t shock was o u r o b s e r v a t i o n of hundreds of t o r t o i s e s i n i n t e r t i d a l areas where no herbaceous v e g e t a t i o n was
p r e s e n t . A t low t i d e we observed t h e s e t o r t o i s e s t o f o r a g e on t h e few l e a v e s t h a t f e l l t o t h e ground, and t o seemingly f e e d on a l g a e on t h e s u r f a c e o f t h e mud. A t h i g h t i d e t h e t o r t o i s e s refuged on rocks, mangrove prop r o o t s , and dead l i m b s , s i m p l y t o a v o i d b e i n g swept away;
many were observed i n t h e r e d mangrove (Rhizophora mangle) zone. I t was obvious t h a t t h i s was a m a r g i n a l , h i g h r i s k h a b i t a t f o r t o r t o i s e s , and i t seemed 1 i k e l y t h a t r e s o u r c e 1 im i t a t i o n f u r t h e r i n l a n d had
p r o b a b l y been t h e impetus f o r such e x t e n s i v e u t i l i z a t i o n o f i n t e r t i d a l areas.
F u r t h e r i n l a n d , v i r t u a l l y a1 1 i n d i v i d u a l s o f f a v o r e d woody p l a n t s p e c i e s e x h i b i t e d a h i gh browse1 i ne, and r e g e n e r a t i on o f t h e s e s p e c i es was s i m p l y n o n e x i s t e n t . There have been s e v e r a l e x p l a n a t i o n s o f f e r e d f o r t h e d r a m a t i c changes i n t h e f l o r a o f Grande T e r r e , and
i n e x p l i c a b l y t h e y seem t o search f o r reasons o t h e r t h a n t h e goats.
F o r example, i t has been suggested t h a t some h i g h b r o w s e l i n e s were caused by t o r t o i s e s p i l i n g up 2 and 3 l a y e r s t h i c k w h i l e s e e k i n g shade. Presumably i n such a s i t u a t i o n a t o r t o i s e would be a b l e t o r e a c h l e a v e s t h a t were n o t n o r m a l l y a v a i l a b l e . The death o f l a r g e numbers o f some species, f o r example, b o i s cassant ( G u e t t a r d a ) has been a t t r i b u t e d b o t h t o t o r t o i s e s a b r a d i n g t h e r o o t s w h i l e s e e k i n g shade, and t o s a l t spray d u r i n g storms. Perhaps t h e s e hypotheses a r e
C o b l e n t z & Van Vuren
c o r r e c t ; however, t h e y f a i l t o account f o r t h e complete absence o f seed1 i ng r e g e n e r a t i o n , and t h e complete d e f o l i a t i on o f a1 1 branches l e s s t h a n 2 m h i g h . These t r e e s a1 1 have h i g h browse1 i n e s caused by goats, and a r e n o t r e p o p u l a t i ng because seed1 i ngs cannot s u r v i ve, even i n areas where t o r t o i s e s cannot go. A d d i t i o n a l l y , i t seems u n l i k e l y t h a t any s t r a n d s p e c i e s i s i n t o l e r a n t of exposure t o s a l t .
We do n o t propose t h a t goats a r e s o l e l y r e s p o n s i b l e f o r m a j o r v e g e t a t i o n changes on Grande T e r r e , b u t r a t h e r t h a t t h e y a r e one m a j o r f a c t o r among s e v e r a l p o s s i b l e causes. T o r t o i s e s and t h e i r f o r a g e r e s o u r c e on A l d a b r a may we1 1 f l u c t u a t e g r e a t l y o v e r t i m e ; i t w i l l t a k e many y e a r s t o d e t e r m i n e if t h i s i s t h e case. Goats, however, g r e a t l y i ncrease t o t a l consumption o f p l a n t biomass, and compete d i r e c t l y and i n d i r e c t l y w i t h t h e t o r t o i s e s f o r food. We be1 i e v e t h a t t h e impact o f goats on A l d a b r a i s a d d i t i v e t o t h a t of t h e t o r t o i s e s , and m a g n i f i e s t h e amp1 i t u d e o f f l u c t u a t i o n i n numbers o f b o t h p l a n t s and t o r t o i s e s , i n c r e a s i ng t h e chances o f e x t i n c t i on o f t h e most s e n s i t i ve endemi cs.
Changes i n woody v e g e t a t i o n on Grande T e r r e a r e a good example o f t h e e f f e c t o f goats. Several a u t h o r s ( H n a t i u k e t al., 1976; Merton e t al., 1976; Swingland and Coe, 1979; Gould and Swingland, 1980) have p r e s e n t e d compel 1 i ng arguments t h a t a t t r i b u t e r e c e n t changes i n t h e v e g e t a t i o n on Grande T e r r e t o f e e d i n g and r e s t i n g a c t i v i t i e s o f t o r t o i s e s . The n e g a t i v e e f f e c t s o f t o r t o i s e s a r e i r r e f u t a b l e ; however, we b e l i e v e t h a t t h e s e e f f e c t s do n o t account f o r a l l t h e damage observed. I n f a c t , we s t r o n g l y d i s a g r e e t h a t t h e t o r t o i s e i s t h e " o n l y s i g n i f i c a n t p r i m a r y consumer" (Coe e t al., 1979) and t h a t
"The impact o f f e r a l goats on t h e g i a n t t o r t o i s e i s minimal on
A l d a b r a " (Gould and Swingland, 1980). I n some areas, goats p r o b a b l y c o n t r i b u t e s i g n i f i c a n t l y t o t h e d e a t h of shrubs, and more i m p o r t a n t l y t h e y p l a y a key r o l e i n p r e v e n t i n g a1 1 r e g e n e r a t i o n of p r e f e r r e d woody species. Furthermore, we a r e c e r t a i n t h a t t h e n e a r l y 2 m h i g h
browse1 i ne observed on Grande T e r r e i s a t t r i b u t a b l e s o l e l y t o goats.
S i nce t o r t o i s e s presumably e v o l ved w i t h t h e v e g e t a t i o n o f t h e i s l a n d , i t seems l i k e l y t h a t t h e p l a n t s p e c i e s a r e capable o f r e g e n e r a t i o n i n t h e presence o f t o r t o i s e s , a t l e a s t i n r e f u g i a where t h e t o r t o i s e s cannot get t o them. Goats r e p r e s e n t t h e o n l y a d d i t i o n a l major source o f h e r b i v o r y on Grande Terre, and a r e capable o f g o i n g where t o r t o i s e s cannot. I t would seem l o g i c a l t o a t t r i b u t e t h e complete l a c k o f
s e e d l i n g r e g e n e r a t i o n t o them.
One f a c t o r s u p p o r t i n g o u r argument t h a t g o a t s a r e c u r r e n t l y a m a j o r c o m p e t i t o r f o r forage on Grande T e r r e i s t h e d e n s i t y o f goats we observed. Gould and Swingland (1980) r e p o r t e d a d e n s i t y o f 10-12 goatslkm2 i n t h e s o u t h e a s t p o r t i o n of Grande Terre. Working i n t h e same area, we k i l l e d 292 goats i n an area of about 8-10 km2, .and many more remained a l i v e . Thus, t h e r e were i n excess of t h e 29.2-36.5
goats/km2 based on k i 11 f i g u r e s alone, a minimum t h r e e - f o l d i n c r e a s e i n t h e decade s i n c e t h e 1977 (Gould and Swingland, 1980) e s t i m a t e .
By c o n t r i b u t i n g t o t h e a c c e l e r a t e d d e a t h o f t r e e s and shrubs, and p r e v e n t i n g a1 1 seed1 i ng r e g e n e r a t i on, goats may be s e v e r e l y l i m i t i n g t h e amount of shade a v a i l a b l e t o t o r t o i s e s . A d d i t i o n a l l y , as f o l i a r a r e a of a p l a n t i s reduced t h r o u g h browsing, t h e number of t o r t o i s e s t h a t can refuge under t h a t p l a n t i s p r o p o r t i o n a t e l y reduced; excess t o r t o i s e s need t o f i n d a new s o u r c e of shade. I n some areas, sources
Coblentz & Van Vuren 5
o f shade a r e f a r a p a r t and e s s e n t i a l l y f u l l y u t i l i z e d , t h u s t o r t o i s e s f o r c e d t o seek new shade p r o b a b l y have a low p r o b a b i l i t y o f s u r v i v a l . The e f f e c t s o f goats upon t h e shade r e s o u r c e may a c t u a l l y be a g r e a t e r i n f 1 uence upon t o r t o i s e numbers and c o n d i t i o n t h a n d i r e c t compet i t i on f o r food.
A c c o r d i n g l y , we have concluded t h a t t h e r e s h o u l d no l o n g e r be any q u e s t i o n o f whether goats s h o u l d be e r a d i c a t e d , b u t r a t h e r a q u e s t i o n o f how soon i t can be implemented. Together we have many y e a r s o f e x p e r i e n c e w i t h f e r a l u n g u l a t e s on oceanic i s l a n d s , and we judged t h e i m p a c t s o f goats on Grande T e r r e t o be as s e r i o u s as o t h e r i s l a n d s where goats have been viewed as agents o f h a b i t a t d e g r e d a t i o n and e x t i n c t i o n o f endemic species. Q u i t e c l e a r l y i n o u r minds, goats on Grande T e r r e a r e a l t e r i n g t h e s p e c i e s c o m p o s i t i o n of b o t h fauna and f l o r a , r e d u c i n g t h e f o r a g e r e s o u r c e a v a i l a b l e t o t o r t o i s e s ,
e l i m i n a t i n g s e e d l i n g r e g e n e r a t i o n , r e d u c i n g shade a v a i l a b l e t o t o r t o i s e s , and p r o b a b l y r e d u c i n g b i o t i c d i v e r s i t y .
On St. Helena, i t took o v e r 200 y e a r s b e f o r e " t h e e v i 1 was complete and i r r e t r i e v a b l e " (Darwin 1860). A l d a b r a would b e t t e r be remembered as t e s t i m o n y f o r s u c c e s s f u l p r e s e r v a t i o n o f i n s u l a r b i o t a , r a t h e r t h a n a requiem f o r one o f t h e w o r l d ' s t r u l y unique ecosystems.
ACKNOWLEDGEMENTS
Many p e o p l e h e l p e d b r i n g t h i s p r o j e c t t o f r u i t i o n . We a r e i n d e b t e d t o M a r c i a S i t n i k , Len Mole, Dr. D.R. S t o d d a r t , and Lindsey Chong Seng f o r smoothing o u t a d m i n i s t r a t i v e d e t a i l s , a r r a n g i n g
f i n a n c i a l a f f a i r s t h a t supported t h e p r o j e c t , and s u p p o r t i n g t h e need f o r t h e work. We e s p e c i a l l y thank o u r boatman and c r e o l e cook, H a r r y Charles, f o r g u i d i n g us around t h e a t 0 1 1 and a1 l o w i n g us t o
c o n c e n t r a t e on o u r task. T h i s p r o j e c t was supported by t h e World H e r i t a g e Program o f UNESCO, t h e S e y c h e l l e s I s l a n d s Foundation, and t h e Oregon S t a t e Uni v e r s i t y A g r i c u l t u r a l Experiment S t a t i o n ( P r o j e c t ORE 00925). T h i s i s Oregon S t a t e U n i v e r s i t y A g r i c u l t u r a l Experiment S t a t i o n T e c h n i c a l Report No. 8288.
C o b l e n t z & Van Vuren
LITERATURE CITED
Coblentz, B.E. 1978. The e f f e c t s o f f e r a l goats (Capra h i r c u s ) on i s l a n d ecosystems. Bio. Conserv. 13:279-286.
Coe, M.J., 0. Bourn, and I.R. Swi ngland. 1979. The biomass,
p r o d u c t i o n and c a r r y i n g c a p a c i t y o f g i a n t t o r t o i s e s on A1 dabra.
P h i l . Trans. R. Soc. Lond. B. 286:163-176.
Darwin, C. 1860. The voyage o f t h e Beagle. 1962 N a t u r a l H i s t o r y L i b r a r y E d i t i o n . Doubleday and Co.: Garden C i t y . 524 pp.
Dupont, R. 1929. Report on a v i s i t of i n v e s t i g a t i o n t o t h e p r i n c i p a l o u t l y i n g i s l a n d s of t h e S e y c h e l l e s Archipelago.
T y p e s c r i p t , 20 pp. Mahe: Department of A g r i c u l t u r e f i l e s . Gould, M.S., and I.R. Swingland. 1980. The t o r t o i s e and t h e goat:
i n t e r a c t i o n s on A l d a b r a I s l a n d . B i o l . Conserv. 17:267-279.
Greenway, J.C. J r . 1958. E x t i n c t and v a n i s h i n g b i r d s of t h e w o r l d . Spec. Publs. Am. Comm. I n t . W i l d l
.
P r o t . No. 13. 518 pp.H n a t i u k , R.J., S.R.J. Woodell, and D.M. Bourn. 1976. G i a n t t o r t o i s e and v e g e t a t i o n i n t e r a c t i o n s on Aldabra A t o l l
-
P a r t 2: c o a s t a l . B i o l . Conserv. 9:305-316.Hutchinson, K.J., and K.L. King. 1980. The e f f e c t s of sheep s t o c k i n g l e v e l on i n v e r t e b r a t e abundance, biomass, and energy u t i l i z a t i o n i n a temperate, sown grassland. J. Appl. Ecol. 17:369-387.
Merton, L.F.H., D.M. Bourn, and R.J. Hnatiuk. 1976. G i a n t t o r t o i s e and v e g e t a t i o n i n t e r a c t i o n s on Aldabra A t o l l
-
P a r t 1: i n l a n d . B i o l . Conserv. 9:293-304.Newing, T.J., H.K. Daly, and K. Hambler. 1984. F e r a l goats on A1 dabra. F i n a l Report, Southampton U n i v e r s i t y E x p e d i t i o n t o Aldabra, 1982. Unpubl.
S t o d d a r t , D.R. 1981. H i s t o r y of goats on t h e A l d a b r a A r c h i p e l a g o . At01 1 Res. B u l l . 255:23-26.
Swingland, I.R., and M.J. Coe. 1979. The n a t u r a l r e g u l a t i o n of g i a n t t o r t o i s e p o p u l a t i o n s on A l d a b r a A t 0 1 1 : r e c r u i t m e n t . Phi 1. Trans.
R. Soc. Lond. B. 286:177-188.
Thorne, R.J. 1967. A f l o r a o f Santa C a t a l i n a I s l a n d , C a l i f o r n i a . A i s o 6:l-77
Van Vuren, D., and B.E. Coblentz. 1987. Some e c o l o g i c a l e f f e c t s of f e r a l sheep on Santa Cruz I s l a n d , C a l i f o r n i a , USA. B i o l . Conserv.
41:l-16.
Wallace, A.R. 1911. I s l a n d L i f e . 3 r d e d i t i o n . Macmillan: London 522 pp.
Wodzicki, K.A. 1950. I n t r o d u c e d mammals of New Zealand. N.Z. Dept.
Sci. Ind. Res. B u l l . 98:l-255.
