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Population control is the practice of artificially maintaining the size of any population. It simply refers to the act of limiting the size of an animal population so that it remains manageable, as opposed to the act of protecting a species from excessive rates of extinction, which is referred to as conservation biology. [1] [2] [3]
While many abiotic and biotic factors influence population control, humans are notably influential against animal populations. Whether humans need to hunt animals for food, exterminate a pest, or reduce competition for resources, managing populations involves providing nourishment, or neutering to prevent reproduction, culling individuals or the use of pesticides. Population control plays an important role in wildlife populations. Based on the species being dealt with, there are numerous ways populations of the wild are controlled. Wildlife contraception is the act of preventing reproduction in the wild, which subsequently decreases populations. An example of this includes the maintenance of deer populations with the use of vaccines. [4] [5] Other methods to maintain populations include lethal trapping, live trapping, egg/roost site manipulation, live-ammunition shooting, and chemical euthanization. Lethal trapping, egg/roost site manipulation, live-ammunition shooting, and chemical euthanization are methods used to eliminate animal populations and prevent reproduction, whereas live trapping captures species to remove them from a specific area. [6]
Population control can be influenced by a variety of factors. Humans can greatly influence the size of animal populations they directly interact with. It is, for example, relatively common (and sometimes even a legal requirement) to spay or neuter dogs. Spaying – removing the ovaries and uterus of a female animal – medical term = ovariohysterectomy. Neutering - removing the testes of a male animal – medical term = orchiectomy. Various humans activities (e.g. hunting, farming, fishing, industrialization, and urbanization) all impact various animal populations.
Population control may involve culling, translocation, or manipulation of the reproductive capability. The growth of a population may be limited by environmental factors such as food supply or predation. The main biotic factors that affect population growth include:
Important abiotic factors affecting population growth include:
Direct human impacts are not the only ways humans can control animal populations. Often times, humans are indirectly controlling animal populations, in other words, the humans are not aware that their actions are controlling animal populations. For example, new infrastructure and roads can lead to animals being displaced from their natural habitat. Their new habitats that they are forced to move to may not provide the same necessities to them that they require for survival. This will result in a decreasing population as a result of human actions.
Animal euthanasia is often used as a final resort to controlling animal populations. In Tangipahoa Parish, Louisiana, the parish performed mass euthanasia on the entire animal shelter population, including 54 cats and 118 dogs that were put to death due to a widespread disease outbreak that spread among the animals. [9]
Neutering is another option available to control animal populations. The annual Spay Day USA event was established by the Doris Day Animal League to promote the neutering of pets, especially those in animal shelters, so that the population remains controllable. [10]
Wildlife contraception is used to regulate populations of animals in the wild and halt reproduction. For example, vaccines are currently being used in deer populations. GonaCon, which was developed by the US Department of Agriculture, encourages the production of antibodies in the sex drive hormones. [4] Specifically, it is said to remove the oestrous cycles from the females, which initially attracts the males; without the oestrous cycles, males are not interested in mating. [4] Another type of vaccine that is being used in deer is called porcine zona pellucida (PZP). [5] PZP works by blocking sperm with antibodies on the deer's egg surface. [5]
When preventing reproduction fails to control populations, methods such as lethal trapping, live trapping, egg/roost site manipulation, live-ammunition shooting, and chemical euthanization are used to maintain populations.
Lethal trapping is a method used to kill animals. This type of method is usually monitored in order to ensure no ethical or public concerns arise. While this tactic is most commonly used on small animals, populations of larger animals such as beavers and foxes are also controlled with this type of method. [6]
Live trapping is a method used to capture a variety of animals. From small animals to large animals, this type of population control method uses barrel traps, restraining snares, and leg-hold devices. Just like the lethal trapping method, this tactic also needs to be regularly monitored to ensure no ethical concerns arise, as well as reduce animal distress. Specifically, this type of population control method is popular with capturing birds. [6]
Egg/roost site manipulation is used on birds to prevent them from nesting in prohibited areas. Water spray is popular in urban and agricultural areas as it uses sprinklers to emit surfactants. The surfactants then control bird populations by killing and preventing future birds from nesting. [6]
Live-ammunition shooting uses firearms to eliminate animals such as birds and bears. Because this type of population control method is restricted in many parts of the world, it is only to be used when other control methods have failed. [6]
Chemical euthanization refers to the use of chemicals to cause an easy or painless death and is divided into three categories: acute toxins, anticoagulants and decalcifiers, and fumigants. [6] [11] Acute toxins only require a single dose to kill animals, whereas anticoagulants and decalcifiers require numerous doses over time. Fumigants are used to suffocate animals underground. [6] While this type of population control method poses ethical concerns, the World Society for the Protection of Animals (WSPA) believes it is necessary when human health or the safety of other animals are at risk. To ensure this control method is humane, WSPA states that it must be painless, achieve rapid unconsciousness followed by death, minimize animal fear and distress, and be reliable and irreversible. [12]
Population control also plays a significant role in managing and controlling invasive species so that they are eliminated before becoming abundant and causing any ecological harm. [13]
Several efforts have been made to control the population of ticks, which act as vectors of a number of diseases and therefore pose a risk to humans. Efforts are also continuously being made to control wildlife populations near airports. Specifically, control measures have been approved for bald eagles and deer. [6]
An animal shelter or pound is a place where stray, lost, abandoned or surrendered animals – mostly dogs and cats – are housed. The word "pound" has its origins in the animal pounds of agricultural communities, where stray livestock would be penned or impounded until they were claimed by their owners.
Neutering, from the Latin neuter, is the removal of a non-human animal's reproductive organ, either all of it or a considerably large part. The male-specific term is castration, while spaying is usually reserved for female animals. Colloquially, both terms are often referred to as fixing. In male horses, castrating is referred to as gelding. An animal that has not been neutered is sometimes referred to as entire or intact.
The white-tailed deer, also known commonly as the whitetail and the Virginia deer, is a medium-sized species of deer native to North America, Central America, and South America as far south as Peru and Bolivia, where it predominately inhabits high mountain terrains of the Andes. It has also been introduced to New Zealand, all the Greater Antilles in the Caribbean, and some countries in Europe, such as the Czech Republic, Finland, France, Germany, Romania and Serbia. In the Americas, it is the most widely distributed wild ungulate.
Trap–neuter–return (TNR), also known as trap–neuter–release, is a controversial method that attempts to manage populations of feral cats. The process involves live-trapping the cats, having them neutered, ear-tipped for identification, and, if possible, vaccinated, then releasing them back into the outdoors. If the location is deemed unsafe or otherwise inappropriate, the cats may be relocated to other appropriate areas. Often, friendly adults and kittens young enough to be easily socialized are retained and placed for adoption. Feral cats cannot be socialized, shun most human interaction and do not fare well in confinement, so they are not retained. Cats suffering from severe medical problems such as terminal, contagious, or untreatable illnesses or injuries are often euthanized.
Animal euthanasia is the act of killing an animal humanely, most commonly with injectable drugs. Reasons for euthanasia include incurable conditions or diseases, lack of resources to continue supporting the animal, or laboratory test procedures. Euthanasia methods are designed to cause minimal pain and distress. Euthanasia is distinct from animal slaughter and pest control.
A feral cat or a stray cat is an unowned domestic cat that lives outdoors and avoids human contact; it does not allow itself to be handled or touched, and usually remains hidden from humans. Feral cats may breed over dozens of generations and become an aggressive local apex predator in urban, savannah and bushland environments. Some feral cats may become more comfortable with people who regularly feed them, but even with long-term attempts at socialization, they usually remain aloof and are most active after dusk. Of the 700 million cats in the world, an estimated 480 million are feral.
The zona pellucida is the specialized area surrounding mammalian oocytes (eggs). It is also known as an egg coat. The zona pellucida is essential for oocyte growth and fertilization.
Reproductive biology includes both sexual and asexual reproduction.
In some countries there is an overpopulation of pets such as cats, dogs, and exotic animals. In the United States, six to eight million animals are brought to shelters each year, of which an estimated three to four million are subsequently euthanized, including 2.7 million considered healthy and adoptable. Euthanasia numbers have declined since the 1970s, when U.S. shelters euthanized an estimated 12 to 20 million animals. Most humane societies, animal shelters and rescue groups urge animal caregivers to have their animals spayed or neutered to prevent the births of unwanted and accidental litters that could contribute to this dynamic.
Wildlife contraceptives, sometimes referred to as wildlife fertility control, are contraceptives used to regulate the fertility of wild animals. They are used to control population growth of certain wild animals.
Broodstock, or broodfish, are a group of mature individuals used in aquaculture for breeding purposes. Broodstock can be a population of animals maintained in captivity as a source of replacement for, or enhancement of, seed and fry numbers. These are generally kept in ponds or tanks in which environmental conditions such as photoperiod, temperature and pH are controlled. Such populations often undergo conditioning to ensure maximum fry output. Broodstock can also be sourced from wild populations where they are harvested and held in maturation tanks before their seed is collected for grow-out to market size or the juveniles returned to the sea to supplement natural populations. This method, however, is subject to environmental conditions and can be unreliable seasonally, or annually. Broodstock management can improve seed quality and number through enhanced gonadal development and fecundity.
Culling is the process of segregating organisms from a group according to desired or undesired characteristics. In animal breeding, it is removing or segregating animals from a breeding stock based on a specific trait. This is done to exaggerate desirable characteristics, or to remove undesirable characteristics by altering the genetic makeup of the population. For livestock and wildlife, culling often refers to killing removed animals based on their characteristics, such as their sex or species membership, or as a means of preventing infectious disease transmission.
Canine reproduction is the process of sexual reproduction in domestic dogs, wolves, coyotes and other canine species.
Nuisance wildlife management is the selective removal of problem individuals or populations of specific species of wildlife. Other terms for the field include wildlife damage management, wildlife control, and animal damage control. Some wild animal species may get used to human presence, causing property damage or risking the transfer of diseases (zoonoses) to humans or pets. Many wildlife species coexist with humans very successfully, such as commensal rodents which have become more or less dependent on humans.
Alley Cat Rescue is an international nonprofit organization, headquartered in Mount Rainier, Maryland, that works to protect cats using trap–neuter–return for community cats; rescue, and neuter before adoption; promoting compassionate, non-lethal population control; and by providing national and international resources for cat caretakers.
Overpopulation or overabundance is a state in which the population of a species is larger than the carrying capacity of its environment. This may be caused by increased birth rates, lowered mortality rates, reduced predation or large scale migration, leading to an overabundant species and other animals in the ecosystem competing for food, space, and resources. The animals in an overpopulated area may then be forced to migrate to areas not typically inhabited, or die off without access to necessary resources.
The National Animal Interest Alliance (NAIA) is a non-profit organization in the United States dedicated to promoting animal welfare and animal husbandry practices, strengthening the human-animal bond, and safeguarding the rights of responsible animal owners and professionals through research, public education and public policy. The NAIA mission is "to promote the welfare of animals."
Compassion and Responsibility for Animals (CARA) is a registered non-profit, non-government animal welfare organization in the Philippines. It was founded in 2000 by a group of animal lovers determined to help the plight of animals in the Philippines. The current president of CARA is Nancy Cu-Unjieng.
In biology, overabundant species refers to an excessive number of individuals and occurs when the normal population density has been exceeded. Increase in animal populations is influenced by a variety of factors, some of which include habitat destruction or augmentation by human activity, the introduction of invasive species and the reintroduction of threatened species to protected reserves.
Compassionate conservation is a discipline combining the fields of conservation and animal welfare. Historically, these two fields have been considered separate and sometimes contradictory to each other. The proposed ethical principles of compassionate conservation are: "first do no harm, individuals matter, inclusivity, and peaceful coexistence".
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