Dietary competition between the black caiman (Melanosuchus niger) and the spectacled caiman




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Nick Reynolds Page 4/22/2016



DIETARY COMPETITION BETWEEN THE BLACK CAIMAN (Melanosuchus niger) AND THE SPECTACLED CAIMAN (Caiman crocodilus) WITHIN THE LAGO PRETO RESERVE, PERU.



Caiman crocodilus Melanosuchus niger


Nick Reynolds

BSc Wildlife Conservation

Durrell Institute of Conservation and Ecology

University of Kent

2007

Abstract:
This research was undertaken to determine the diets of the Spectacled Caiman (Caiman crocodilus) and Black Caiman (Melanosuchus niger) within the Lago Preto Conservation Concession, Peru. This was done as dietary competition may be one of the ecological factors affecting the lack of recovery of the Black Caiman in this area. The diets of the two species were determined similar, using the numerical and frequency occurrences of certain pre-determined prey categories found in stomach samples. A dietary overlap index showed the overlap was biologically significant within both habitat types surveyed. Results were compared to previous studies and the comparisons highlighted similarities. A comparison to results from a different region of Peru showed differences in diet preferences for the two species. However, both studies highlighted dietary competition.
This research underlined further study is required to collaborate caiman size and diet of the two species within Lago Preto. Further comparative study between different regions of South America is also highly recommended.
1.0 Introduction:
The Black Caiman (Melanosuchus niger) and the Spectacled Caiman (Caiman crocodilus) are the two largest crocodilians in the Amazon basin, and both species have a long history of human exploitation (Smith, 1980).
The Black Caiman is the largest Neotropical predator. The species was formerly abundant in South America and present in the entire Amazon basin. During the last century the Black Caiman along with the Spectacled Caiman have faced strong hunting pressure for the leather industry, and a high rate of habitat loss (Smith, 1980 and Plotkin et al, 1983). Although these pressures have reduced greatly due to legal protection within most of their range, they seem to have had stronger adverse effects on the Black Caiman. The Black Caiman’s life history and ecological traits are believed to limit its recovery. The species is known to have a sedentary diet and to be a habitat specialist found in slow-moving freshwater rivers, lakes, wetlands, black water swamps, and seasonally flooded areas of the Amazon (De Thoisy et al, 2006).
As a result, the total species population size of Black Caiman may have decreased by 90%, and concomitantly has experienced a high level of fragmentation (Ross, 1998).
The Black Caiman competes ecologically with the Spectacled Caiman (Caiman crocodilus), which is believed to be a much more opportunistic species (Rebelo and Magnusson, 1983, Herron, 1991, Herron, 1994 and Thorbjarnarson, 1991). Spectacled Caiman population recovery rates have been measured at four times higher than the Black Caiman (Farias et al, 2004 and De Thoisy et al, 2006). To date, field surveys have been irregularly conducted all over both species range; but available data reveal that the Black Caiman is locally extinct in many Amazonian areas, and occurs in reduced densities in many others (Rebelo and Lugli, 2001).
On the other hand, field observations indicate that some populations may have recovered (Rebelo 2001). Unfortunately the Black Caiman population within the Lago Preto Reserve in the North-Eastern Peruvian Amazon is not one of these fortunate populations. In this study the diets of the Black Caiman and Spectacled Caiman were analysed. This was achieved by taking stomach samples to investigate the factor of diet within the ecological competition between the two species. This research will hopefully help take another step towards understanding why the Lago Preto population of Black Caiman are struggling to recover.
1.1 The Study Animal:

The Black Caiman (Melanosuchus niger)

Common names:

Black Caiman, Caiman, Caiman Negro, Caiman Noir, Lagarto Negro, Jacare Acu, Jacare Assu, Jacare Acu, Jacare Uassu, Jarace Una, Yacare Assu.


Distribution:

Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Perú and Venezuela (Unconfirmed) (See Fig 1)



Fig 1

Habitat:

Found in various freshwater habitats (e.g. slow-moving rivers, streams, lakes and flooded savannah and wetlands). Although overlapping with the range of other caiman species in South America, it appears to occupy different habitat niches

(http://wwwflmnh.ufl.edu/cnhc/csp_mnig.htm).
Status:

CITES: Appendix 1,

IUCN: Red List: Low risk, conservation dependent

Estimated wild population: 25,000 to 50,000

Summary: Widely distributed, but historically heavily exploited. Most populations appear to be recovering well (http://www.CITES.org).
Diet:

The Black Caiman eats fish (including Piranha and Catfish) and aquatic vertebrates, including large Capybara rodents (Hydrochaeris hydrochaeris). This species shows more terrestrial hunting activity, particularly at night, having acute sight and hearing. Juveniles take crustaceans before moving onto larger terrestrial prey. Larger adult caiman of this species have been reported to attack domestic animals and humans (http://www.flmnh.ufl.edu/cnhc/csp_mnig.htm).



Group of Black Caiman hatchlings demonstrating the safety in numbers strategy.
(http://www.flmnh.ufl.edu/cnhc/csp_mnig.htm)

Juvenile Black Caiman (www.pbs.org/.../images/whos-blackcaiman.gif)


Conservation:

Historically the distribution of the Black Caiman has been widely distributed throughout the Amazon basin and beyond. However, once populations of both Crocodylus acutus (American crocodile) and Crocodylus intermedius (Orinoco crocodile) became severely depleted due to over-zealous commercial hunting, attention was turned to those species with slightly smaller or lower-grade skins (Best 1984).


The skin of the Black Caiman produces shiny, black leather. Hunting was directed very intensely towards the Black Caiman during the 1950’s. Some areas were affected more severely than others, with hunting pressures continuing into the 1970’s and beyond. However, within the 1970’s, a major shift in caiman hunting occurred in the Western Brazilian Amazon (Amazonas state). As markets for skins disappeared, hunters began selling the meat of caiman instead. By the early 1980’s, a trade in salted meat from the Amazonas to Para state in Brazil to Colombia was reported, and this trade continues to flourish (Best 1984).
The Black Caiman is estimated to have been reduced in numbers by 90% in the space of the last century. Population recovery today is impeded both by continued illegal hunting and through increased competition with the more numerous Caiman crocodilus (Spectacled Caiman). This latter species has moved into areas once inhabited by the Black Caiman and proliferated due to its increased reproductive capacity. Hunters can take both species with ease. Habitat destruction through deforestation and burning of swamplands (e.g. French Guiana) continues the onslaught

(http://www.flmnh.ufl.edu/cnhc/csp_mnig.htm).

Little information was available about this species until the 1980’s, when research was carried out into both biology and population ecology. There is still much to be learnt however. Although some data is available concerning interactions with other South American Caiman species, the dramatic decline in populations of the Black Caiman have obscured trends

(http://www.flmnh.ufl.edu/cnhc/csp_mnig.htm).


Population declines have been correlated with a decrease in fish production in rivers. This is believed to be due to the removal of the nutrient-recycling component in the ecosystem as provided by apex predators such as Caiman. Both Piranha and Capybara have benefited from the reduction of their main predator. This had led to increased agricultural and livestock losses. Survey data, which is available throughout most of the species range, reveals drastically reduced populations. Further survey work is required to update this information. The Black Caiman is severely depleted in over half of the countries in which it occurs, and considered to be depleted in the rest. Only populations in isolated locations remain stable (http://www.flmnh.ufl.edu/cnhc/csp_mnig.htm).
Management programs centre on the legal protection of remaining wild populations, but these laws are difficult to enforce effectively. Captive breeding and reintroduction was initiated in Bolivia in 1990. Both of these conservation strategies need to be extended and implemented as effectively as possible in other countries (http://www.flmnh.ufl.edu/cnhc/csp_mnig.htm).

The Spectacled Caiman (Caiman crocodilus)

Common names:

Common Caiman, Spectacled Caiman, Tinga, Baba, Babilla, Babiche, Cachirre, Caiman blanco, Caiman de Brasil, Cascarudo, Jacaretinga, Lagarto, Lagarto Blanco, Yacare Blanco.



Subspecies:

  • C.c.apaporiensis (Rio Apaporis Caiman)

  • C.c. fuscus (Brown Caiman)

  • C.c. yacare (Yacare Caiman)

(http://www.flmnh.ufl.edu/cnhc/csp_ccro.htm#dist)
Distribution:

Brasil, Colombia, Costa Rica, Cuba*, Ecuador, El Salvador, Guyana, French Guiana, Guatemala, Honduras, México, Nicaragua, Panamá, Perú, Puerto Rico*, Suriname, Tobago, Trinidad, United Status, and Venezuela. [*=Introduced – C.c.fuscus in Cuba and Puerto Rico]. (See Fig. 2.0)



Fig 2.0

(http://www.flmnh.ufl.edu/cnhc/cst_ccro_dh_map.htm)


Habitat:

The Spectacled Caiman is an extremely adaptable species found in virtually all lowland wetland and riverine habitat types throughout its range, particularly as a result of the now-diminished ranges of sympatric competitors (e.g. C.acutus, C.intermedius, M.niger).

The Spectacled Caiman has the widest distribution of any species in the Alligatoridae family, it can tolerate a reasonable degree of salinity and if environmental conditions become too harsh it will burrow into mud and aestivate

(http://www.flmnh.ufl.edu/cnhc/csp_ccro.htm#dist).

.


Status:

CITES: All subspecies Appendix 2, except C.c.apaporiensis (Appendix 1)

IUCN Red List: Low Risk, Least concern.

Estimated wild population: Over 1,000,000

Summary: The Spectacled Caiman is the most common of all crocodilian species, although some populations are locally depleted (http://www.CITES.org).
Diet:

Juvenile Spectacled Caiman take a variety of aquatic invertebrates (insects, crustaceans, molluscs). As they grow, various vertebrates make up a greater percentage of the diet. These include fish, amphibians, reptiles and water birds. Much larger, older animals are capable of taking larger mammals such as bush pigs. Past observations have shown that the drier the conditions become the less the caiman feed, cannibalism is common at this time

(http://www.flmnh.ufl.edu/cnhc/csp_ccro.htm#dist).

.

The ecological importance of this species has been demonstrated in terms of nutrient recycling- its nitrogenous waste re-enters the ecosystem to the benefit of other plants and animals. In areas where the Spectacled Caiman has become depleted, fish populations have also been shown to decline. It has also been reputed to control Piranha numbers; however there seems little evidence to support this. In reality, it is likely that the Spectacled Caiman is very much a generalist and adaptive predator, given its ecological success (Silveira+Magnusson 1999).


Juvenile Spectacled Caiman (Caiman crocodilus)

(http://www.flmnh.ufl.edu/cnhc/csp_ccro.htm#dist)
Conservation:

This species has actually benefited from commercial utilization and over-hunting of other species within its range (Crocodylus acutus, C.intermedius and Melanosuchus niger), taking over habitat from which it would otherwise have been out-competed by healthy populations. The skin of the Spectacled Caiman is not ideally suited to tanning, as the ventral scales contain well-developed osteoderms. Only the lateral flanks provide skin of an acceptable quality for tanning. Hunting pressures on this species remained relatively low until the 1950s. By this time populations of the sympatric crocodilian species became depleted and hunting of the Spectacled Caiman intensified. The numbers of caiman harvested since then has been huge, and they currently supply the vast majority of the hide market in America. Leather from this species is often passed off as the American Alligator (Alligator mississippiensis) or other species

(http://www.flmnh.ufl.edu/cnhc/csp_ccro.htm#dist).
Despite pressure from hunting and also collection for the pet trade, existing surveys suggest that populations are in relatively good condition in most areas. This seems to reflect the adaptability of the species, its reproductive potential, and the increase in available habitat through the removal of competing species. Also an increase in man-made water bodies (e.g. Brazilian patanal) has also had beneficial affects. However, it is these factors which make it difficult to determine the overall status of the species, as populations are faring less well in other areas- surveys reveal severe depletion in El Salvador. More up to date surveys are required for clarification, and to examine the interactions between different subspecies. The major threat to this species and others is currently illegal hunting. Smuggling rings operating through Thailand and Singapore are extremely damaging to individual populations, and greater controls and more effective legislation are required

(http://www.flmnh.ufl.edu/cnhc/csp_ccro.htm#dist).


Sustainable use programs are well developed in several countries. Most of these rely upon regular cropping of wild populations. The long term effects of this cropping need to be investigated. The reproductive potential of this species makes properly controlled sustainable yield programs look promising. Farming and ranching programs, while they exist, may be uneconomical in the long run, given the value of the hide and the number of animals which need to be culled in order to produce a profitable amount of hide (Gorzula+Seijas 1989).
1.2 Identification of Species:

The Black Caiman (Melanosuchus niger):

(Wermuth + Fuchs 1978)

The Black Caiman is the largest species in the family Alligatoridae (males can reach at least 4 metres and huge 6 metre specimens have been reported but not confirmed). General appearance is not dissimilar to the American Alligator (Alligator mississippienis). As the common name suggests, they have a dark colouration. The lower jaw has grey banding (brown in older animals), and pale yellow or white bands are present across the flanks of the body; although these are more prominent in juveniles. This banding fades only gradually as the animal matures. The Black Caiman is structurally dissimilar to other caiman species, particularly in the shape of the skull. The Black Caiman has distinctly larger eyes, and a relatively narrow snout. The bony ridge extending from above the eyes down the snout, as seen in other caiman, is present.

(www.flmnh.ufl.edu/cnhc/csp_mnig.htm)
The Spectacled Caiman (Caiman crocodilus):

(Wermuth + Fuchs 1978)

The Spectacled Caiman is a relatively small to medium sized crocodilian (males generally reach 2.0 m to 2.5m, with the largest specimens reported to approach 3m- but these are undoubtedly rare). Females are smaller, reaching a mean maximum size of 1.4m, and rare individuals may approach 2m. Its common name derives from a bony ridge which is present between the front of the eyes (infra-orbital bridge), appearing to join the eyes like a pair of spectacles. A triangular ridge is present on the heavily- ossified upper eyelids, vaguely reminiscent of those on the dinosaur Allosaurus. Juveniles are yellow in colour with black spots and bands on the body and tail. As they mature, they lose this yellow colour and the markings become less distinct. The adults are dull olive- green. The different subspecies vary in colour, size and skull shape.

(www.flmnh.ufl.edu/cnhc/csp_ccro.htm)


1.3 The Study Site:

The Lago Preto Conservation Concession:

The Lago Preto Conservation Concession (LPCC) was awarded to the Wildlife Conservation Society (WCS) in August 2006, and the WCS manage it in collaboration with the Durrell Institute of Conservation and Ecology (DICE). It is located approximately 175km southeast of the city of Iquitos along the Yavari River; the concession is 9926.19 ha in area.

The Yavari River forms the southern border of the concession area. The river, winds through the Amazonian lowlands forming the border between Brazil and northeast Peru. To the north and east the concession area is bordered by the Iquitos-Yavari logging concessions. The concession area gains its name from the local oxbow lake, which is one of a system of several oxbow lakes in the floodplain forests on the Peruvian side of the Yavari River.


Fig 3.0: The coordinates of the limits of the Lago Preto Conservation Concession


Point

UTM

East

North

SW corner

857949

9503866

NW corner

857943

9509773

NE corner

872019

9509711

SE corner

872005

9504831

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