Just a couple of points from me...
Genetic Theory
Average generation length is just one factor in determining the sustainability of genetic variability. Effective population size (N subscript e) is an appropriate substitution for number of organisms. In North America the high proportion of female elephants reduces the effective population to roughly half (86.7) of what the effective population currently would be with an equal proportion of females and males (157). The effective population is further limited because elephants live in matriarchal societies with closely related females, and bull elephants often breed with more than one of these females before being shipped off. Smaller animals (that aren’t flighty) can be shipped via airline across continents or oceans making transfer across institutions easier than for larger animals. This tiny gene flow can have disproportionate positive effects on genetic variability and international cooperation would cause greatly increased genetic diversity in small animals.
Generation Length
Generation length tends to increase with increasing size, but certainly not linearly, and certainly not across all lineages or taxa. Pteropus bats can live up to 30 years in captivity, and individuals typically live 9-17 years. (Popelka, V. and K. Francl. 2006. Pteropus rodricensis (On-line) Animal Diversity Web. Accessed February 03, 2008 at
ADW: Pteropus rodricensis: Information.). Rodriguez fruit bats reach sexual maturity between 1 and 2 years of age, and only have one young at a time. Their generation length is probably not that different from the 7 years calculated for tigers. Parrots are much smaller than tigers, but have significantly higher generation times that better approximate those of 500 times heavier elephants!
Space
Even if a small rodent needed 20 times the captive population as elephants or other large mammals they would still take up considerably less space. The WAZA minimum standards of space for most small rodents are 1500th that for a similar sized group of elephants, or one three hundredth of that required for tigers. A lot of primates have one thirtieth the minimum floor space requirements of elephants an one tenth of the minimum space requirements for giraffes.
The greater propensity for zoological exhibits of small animals to be in mixed species displays compared to most really large mammals like whales and polar bears further reduces the amount of space required to display more diminutive species.
Exhibit/Enclosure Number
In Australia the limited number of Zoos makes it more difficult to provide the increased individual spaces required for animals with shorter generation times, however this is not the case in North America and Europe. The problem may be alleviated somewhat by having a couple displays of the same species at one facility or off exhibit holding.
Management
Smaller animals with shorter generation times may require more transfers and records, but currently these costs constitute only a small percentage of the overall budget of a Zoo. Small mammal displays can often be very flexible in species holding. This characteristic makes it easier to manage spaces. Longer generation times decrease the capability for institutional responsiveness to events like an unforseen animal death, especially in tightly managed populations with few spares.
Financial Spinoffs
It is a common perception that elephants and other large charsimatic animals are a financial asset to institutions because they increase attendance. Number of visitors is only part of the story. I think visitors judge the value of their visit partially on how long they get to spend time together with family and/or friends etc. and still be entertained. The average visitor is not going to spend half an hour looking at just one large species. If you make visitors wander though a large number of smaller exhibits that still contain interesting species like monkeys, small carnivores, active rodents, bats, fish, birds, etc. in a more complex environment I think you can increase the duration of their visit. If you increase visit length you can raise admittance prices and increase the percentage of visitors who stay and eat at your Zoo. Having multiple species increases the probability of having different experiences each time you visit the Zoo. This can greatly increase repeat visitation which not only increases admittance but also helps entrench conservation and education issues/information better in visitors minds.
New exhibits at Zoos require significant fund-raising initiatives. Animal Welfare groups love to jump on projects revolving around large megafauna. This pressure can make it significantly more difficult to raise funds from government representatives who want to circumvent conflict, and private companies that are worried about negative publicity. The commotion aroused by animal activists about the Calgary Zoo’s Project Discovery has been centered around the display of polar bears and whales. This controversy has been further utilized to muddy the overall image and reputation of the Calgary Zoo.
Education
Displaying lots of large megasfauna charismatic mammals at the expense of a greater diversity of forms presents a representation of nature that is incredibly biased. Bats alone constitute over 20% of mammal diversity and rodents constitute another 40%. Despite this reality a lot of Zoos have no representatives of either Order , but several species of large cats. A lot of American Zoos exhibit 0 invertebrates. Although I understand the difficulties in exhibiting some of these animals I don’t understand how forgoing adding several invertebrates and small mammals when you currently don’t have any to add another bear species increases visitor education.
The biggest terrestrial animal in Australia is the Red kangaroo. Their maximum weight is just under 200 pounds. A lot of biodiversity hotspots and threatened habitats have no species of large
charismatic mammals. Something else about these areas has to encourage people to protect them.
A lot of visitors come into a Zoo already having a respect for large charismatic animals. The problem is getting visitors to care about and understand the rare flowers and butterflies inhabiting the meadow by their city that is scheduled for development.
Having 20 times the species provides the potential for 20 times the interpretive/educational signs and devices. There’s also more opportunity for people to be inspired by different animals and identify with different behaviors.
Nature is not composed of separate entities (species), but rather an intricate web that directly or indirectly connects every living organisms to every other one. An elephant does not live in isolation it needs other species to survive. These concepts are more easily realized by visitors viewing an exhibit with many small and medium animals and a maybe a couple of large less demanding species exhibited with plants in a zoogeographic section with interpretive devices illustrating the connections between them.
Conservation
It’s usually much more affordable and practical to provide ex-situ conservation help for smaller species. The Calgary Zoo has successfully bred and been involved in the release of critically endangered Vancouver Island Marmots, and Whooping cranes. Northern leopard frog tadpoles have been captured from healthy populations, raised, and later released to reestablish threatened populations. Swift fox have also been released into the Canadian prairies where they were formerly extirpated, and since then have expanded their range and population in the wild. Extensive research has been carried out by Calgary Zoo staff about the factors influencing the success of these introductions and how behaviour and biology contribute to the success of reintroductions. Extirpated burrowing owls have also been studied and released into the Canadian prairies.
Larger mammals are easier to observe and track in the wild. In part because of this the majority of research is focused around larger organisms and vital information like population size, behavior, seasonality of breeding, habitat preferences, etc. is missing for smaller organisms Research conducted on smaller animals in Zoos can have a significant impact on wild populations. Raccoons formerly kept at the Calgary Zoo were given different nest boxes and their ability to extract food within was used as a form of testing the effectiveness of different eastern bluebird nest designs in combating raccoon predation.
Zoo Research analyzing the suspect ability of different frog species to the chytrid fungus, other diseases and solar radiation could help wild populations significantly more than research done on captive elephants to increase the effectiveness of artificial insemination.
The increased money gained from large mammal exhibits does not necessarily go straight to their conservation, in fact the majority of American Zoos do not directly support Elephant conservation, even if they do provide monetary support for other conservation initiatives.
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