Animal Studies 2 Class Notes 2022 PDF

# Animal Studies 2 (ANS260S) ## Class notes fourth term ### Lecturer: Prof. R. Snyman #### [email protected] ## Introduction to Ethology and Animal Communication: - No class notes available. - Please listen to the slide presentation. - This topic is not for assessment. - Knowledge of the basic co...

# Animal Studies 2 (ANS260S) ## Class notes fourth term ### Lecturer: Prof. R. Snyman #### [email protected] ## Introduction to Ethology and Animal Communication: - No class notes available. - Please listen to the slide presentation. - This topic is not for assessment. - Knowledge of the basic concepts will be required for this module. ## Predator and Prey Interactions - Predation is often portrayed as a series of interactions between two players, the predator and its prey. - The behavior of the predator leads to defense responses by prey that may be countered by the predator and so on. ### Stages of Predation - Encounter - Detection - Identification - Approach - Subjugation - Consumption - Prey wish to interrupt this sequence as soon as possible with defenses. - Predators wish to conclude the process as soon as possible with counter defenses. - Predators are adapted morphologically to catch their prey in the most effective way. - Adaptations depend on the environment and the prey. - These adaptations may include: - Long well-developed teeth (canines) - Sharp claws and beaks - Agility and speed - Strength and stamina - Venom etc. - Prey is adapted to avoid predators (e.g. crypsis and mimicry) or to flee (e.g. section on African predators and prey). ### Generalists and Specialists - Virtually all predators eat more than one prey type (either different species or phenotypes within a species). - Many predators prey more intensely on the most common phenotypes or species – **apostatic selection**. - Predators form a search image of their prey. - The more abundant the prey species, the easier and faster the search image is formed. - Note that the prey species must also be of optimal energy value to the predator, of course. ### Optimal Search Strategies - Within a single patch, a predator has the option of either searching the entire patch, increasing the probability of randomly encountering prey (optimal search hypothesis). - Or spending more time viewing particular sections of a patch, increasing the probability of detecting prey that is already in the field of view (stare duration hypothesis). - The optimal search option increases the risk of not being able to detect and identify some prey items, whilst the stare duration option increases the risk of not encountering that many. - The actual search method used by a predator will reflect a balance (trade-off) between encounter frequency and detection probability. - If a predator can do both, i.e. spend more time in a patch and stare for longer at each visual field, then both detection rate (prey/min) and accuracy (fraction discovered) will increase during the course of foraging as the predator learns to adjust its search rate and stare duration. ## Methods Used by Prey to Reduce Detection, Capture and Consumption: 1. **Polymorphism** - The presence of two or more distinct forms (morphs/phenotypes) in the same population of a species. - May range from: - Seasonal differences - Differences between the two sexes (sexual dimorphism) - Differences between adults and juveniles - Several different forms at a given time. - Polymorphism didn’t necessarily evolve as a defense mechanism but originally served for: - Mate selection - Exploitation of different habitats or food sources. - In those species, polymorphism was, by chance, also useful against predators (a preadaptation to predation). - For species with apostatic predators, polymorphism reduces the overall risk per individual because there are two or more rare forms rather than a single common form. - This affects the formation of a search image by the predator, thus polymorphism operates during the identification stage of predation. - The predator may even switch over to equally abundant but monomorphic prey species because the latter appears to be more abundant. - It must be remembered that these “rare forms” will eventually become common if not preyed upon, which will lead to apostatic predation on them. 2. **Defense Signals** - Many prey species display behaviors or physical features that send specific warning messages / signals to their predators. - The purpose is to deter the predator from attacking. - The signal operates during the approach stage of predation. - Signals include: - Specific body postures - Movements - Patterns on the body etc. 3. **Crypsis** - A prey's colour pattern is cryptic if it resembles a random sample of the visual background as perceived by the predator. - Since the prey are blending into the ackground, crypsis operates during the detection stage of predation. - Species can be polymorphic with all forms being equally cryptic (but in different ways). - The same cryptic colour pattern can be used both as an antipredator defense and for other purposes such social behaviour. - Being cryptic doesn’t necessarily mean looking dull. - For example, in a brightly coloured tropical habitat, bright plumage of parrots is remarkably difficult to see. 4. **Noxiousness** - This refers to prey defenses that include the use of chemicals, either for foul smells, poisons or bad tastes. - Noxiousness often operates during the last two stages of predation (subjugation and consumption). - There is a serious risk to the prey of being killed. - How could noxiousness evolve? - If the predators are inefficient killers, or the defense works well enough so that some prey escape to reproduce, then natural selection will favour noxiousness. - Poisons are also fast-working, so that predators can easily associate feeling unwell with the food they ate. - To strengthen predators’ learning, noxious prey species do not tend to hide from Predators. - They are often found in high densities or aggregations (kin selection) out in the open (gregariousness). - They also often have bright conspicuous colours (aposematic colouration). - The predator learns to associate bad taste or feeling unwell with the striking appearance of the prey and learns to avoid them (at which time it is then operating at the approach stage of predation). - This will not work nearly as well at lower prey densities – the predator will have forgotten the colour pattern by the time it catches the next individual! - Also see Müllerian mimicry. 5. **Mimicry** - This refers generally to one organism (the mimic) taking on the characteristics of another (the model – usually another species), in order to send a clear message to others, in this case to predators. - It is often no more than a bluff. - Mimicry mostly operates during the detection, identification and approach stages of predation. - **Müllerian mimicry** - This refers to less noxious (but not harmless) species resembling more noxious species by means of colour patterns (aposematic colouration) or behaviour. - **Batesian mimicry** - This refers to a palatable and harmless species mimicking a harmful or noxious species. - This is done either by taking on the general appearance of that species or only a specific characteristic. - **Sex-limited mimicry** - This is a type of Batesian mimicry where only one sex displays mimicry. - **Automimicry** - This refers to an individual mimicking another of the same population. - This is not active mimicry and has not even developed through evolution. - The mimic automatically mimics the model, simply because it looks the same. - **Mimesis** - Many biologists consider this a type of crypsis. - In this case, the animal does not only blend in with the background but actually looks like specific objects in the environment, e.g. leaves. - Some predators also use mimesis but instead of mimicking something in the environment, they, or parts of their bodies, mimic objects/food that will attract prey. ## Which Defenses Should Be Used? - Which of the above listed defenses are actually used by prey depends on their relative costs and benefits and the evolutionary history of the species. - It is of course to the prey's benefit to interrupt the predation sequence as early as possible. - This is because: - Risk of death increases as the predation sequence progresses. - Energy used on defenses increases with predation stage. - An early escape leaves more energy for growth and reproduction. - It must be remembered that reproductive and physiological state of a prey individual may at any given time influence whether it will fight or flee. - It may even influence its crypsis (e.g. change in coat thickness and colour). ## Defense Mitigation by Predators - It is clear that predators tend to use more general predation methods early in the predation sequence and more specialized methods later. - Methods used early apply to most prey, e.g. good and diverse sensory systems, speed, agility, strength, learning ability etc. - Methods used later in the sequence are more specific and include, for example, disarticulating jaws of snakes, venom, devices for crushing prey with shells etc. ## Predator-Prey Interactions in an African Context ### The Large Predators and their Prey - The African predators that you are expected to study are the: - Lion (*Panthera leo*) - Cheetah (*Acinonyx jubatus*) - Leopard (*Panthera pardus*) - Spotted hyaena (*Crocuta crocuta*) - African wild (hunting) dog (*Lycaon pictus*) - Black-backed jackal (*Canis mesomelas*). - Observations of large African carnivores show that they are generalists as well as apostatic predators, feeding more intensely on the most common species. - They also select their prey carefully from a population. - Hans Kruuk (a well-known researcher of African carnivores) observed that hyaenas choose individual prey that show abnormal behaviour, e.g. limping. - Animals that have been darted and anaesthetized, immediately get targeted by hyaenas when they recover (and seem normal to humans). - Predators tend to “test” a group of prey first, then select the target. - Hyaenas and wild dogs follow the group until they decide on a target. - Sometimes the leader will identify the target. - Single lions lie and stare at a group of prey for a long time, after which they will run through the group and chase their target. - Predators in general may change their choice quite suddenly and catch whatever individual is more available. - This happens for example when an animal runs into a fence or falls into a waterhole. - Prey selection is of great benefit to predators because it saves a lot of energy. - It is actually also beneficial to the prey, because healthy animals survive to reproduce (survival of the fittest). ### Predators in Areas Where Prey is Scarce - In areas where the prey is scarce, predators are less selective. - Lions in the Ngorongoro have learnt that it is easier to steal hyaenas' prey than to hunt themselves. - The hyaenas are very strictly territorial and excellent group hunters. ### Cooperative Hunting - Some African predators make use of **cooperative hunting** (group hunting), particularly the wild dog and hyaena. - This enables them to: - Catch larger prey items. - A group of hyaenas of >21 can bring down a zebra and will even run straight through a herd of wildebeest to catch the zebra (more meat per hyaena for less energy used). - Be more effective at hunting (more sure of success). - Effectively utilize a greater part of the prey – a lion cannot eat an entire zebra. - Defend prey more effectively against scavengers. - Provide food to members of the group that do not hunt (e.g. wild dogs that stay behind to tend to the pups). ### Disadvantages of Cooperative Hunting: ## Anti-Predator Behaviour and Adaptations - Anti-predator behaviour and adaptations are varied. - Here follows a list but also read Delaney for extra information. - Long legs in the Bovidae (for fast running and agility). - Hooves in Bovidae to protect toes during running. - Horns (Bovidae), teeth, quills. - Bovidae: Eyes on sides of head for larger visual area. - Cryptic colour and patterns (giraffe and zebra). - Advertise “uncatchability” by means of defense signals (e.g. facial patterns and stotting – see later) and noxiousness (e.g. spraying by skunks). - Higher reproductive potential than the predator, often increased when the population decreases (eland can produce two calves per year when the first calf is removed). - Keep a specific distance between them and the predator (the flight distance). - Bunching together and showing horns (buffalo) or even attacking (mobbing) and injuring. - Stotting behaviour in gazelles (warns others, may cause predator to attack too soon but mainly used to warn predators of “uncatchability”). - Fleeing in all directions (confuses predator). - Eat placenta of newborn (limiting smells). - Avoid thickets. - Walk in single file (e.g. impala). - Noting wind direction. - Educate offspring. - Interaction with other species (e.g. baboons and gazelles) for protection (polyspecific groups) – safety in numbers. - Distract predator (lure away). - Herd breaks up into groups for drinking turns. - Adjust drinking times. - Inaccessible nesting areas (e.g. steep cliffs). - Loud screams when attacked – confuses predator. ## Home Range and Territoriality ### Home Range - The home range of an animal is the total area where the animal can be found at any given time. - Home ranges may overlap and animals may meet there without fighting. - Animals that are not territorial do not defend any parts of their home range, except the nesting site during the breeding season. - Territorial animals have territories within the home range (often much smaller than the home range), which they actively defend (but areas around territories are not defended). ### Factors that Influence the Size of the Home Range - Size of the animal. - Density / dispersal of food. - Selective versus unselective species. - Quality of the habitat (stable versus unstable). - Mobility of species. - Age, gender of individual. - Size of the social group. ### Core Area - The home range has a core area (center of activity), usually where the best resources can be found. - It is used for shelter, nesting, sleeping, feeding and drinking. - Territories may be established in this core area. ### Movements Within the Home Range - Movements within the home range can be divided into the following categories: - **Localised movements:** These are short distances to and from the "nest”, to e.g. the drinking and feeding sections of the core area. - In some species localized movements may be extended, where animals move from dry to moist areas during the dry season and back again in the wet season. - **Migration:** The home range is moved seasonally over very large distances. - These movements are predictable and are regular annual occurrences. - **Nomadic movements:** This occurs in species that live in arid zones. - Movements are not seasonally bound and are unpredictable. - Usually, they also occur over long distances. ### Territories - A territory is a defended area within the home range of the animal. - Holding and defending territories is not feasible if resources (especially food) are not stable or concentrated. - Thus, an area must be worth defending – benefits must outweigh the energy and time spent defending! - For this reason, most mammals are not territorial. - Their home ranges are generally too large and resources too widespread (energy costs to defend such large areas are too high). - Of all mammals, the Bovidae have by far the most advanced and varied territorial behaviour. ### Benefits of Holding Territories: - Dispersing of the population – this prevents inbreeding and overcrowding (reducing competition and the spread of diseases and protecting the habitat against overutilization). - Ensuring the genetic fitness of the population by ensuring that the best genes are passed on to the next generation (only the fittest males will gain and successfully defend territories). ### Disadvantages of Holding Territories: - May increase the population's susceptibility to predation (territorial behavior may make them more noticeable and may reduce the numbers of conspecifics that can fight together). - A lot of time and energy is used in defense of territories. - Fights between competitors are costly! ## The Main Types of Territories Held by Mammals - Mostly occurring in Carnivora, Primates, Perissodactyla and Artiodactyla: 1. **Territories Held Permanently by Individual Males and/or Females** - These are solitary animals. - Examples: Leopard, cheetah, caracal, bushbuck, steenbok, grysbok, white rhino, house cat. 2. **Territories Held by Pairs** - These pairs are often monogamous. - Young stay in the territory until they are adults. - Examples: Klipspinger, dik-dik, duiker, black-backed jackal. 3. **Males Hold Mainly Resource Territories for the Purpose of Breeding** - Displayed by many Bovidae. - Males may hold territories only in the breeding season or for longer periods. - Males make use of territorial displays. - Examples: Gazelles (e.g. springbok, impala), waterbuck, blesbok, bontebok, hartebeest, eland, wildebeest, roan and sable antelope. 4. **Territories Held by Groups on a Fairly Permanent Basis** - The size of the group is related to availability of resources. - Example: Baboons, wild dogs, hyaenas, lions, wolves. ## What Influences the Number of Territories and the Shape and Size of Territories? - **Competitive influence:** - In the case of denser populations, animals may hold smaller territories, i.e. the size of the territory is related to the number of competitors (which in turn is related to the food supply). - Animals may reduce their territories as population density increases or increase the territory when a neighbour dies. - **Site influence:** - Animals may have smaller territories around specific sites, e.g. only around the nest site. - Some have nesting and feeding territories, where they may display different behaviour – they may be more or less tolerant of others, depending on how close the others get. - **Time influence:** - Some territories are seasonal. - If an area is valueless at a certain time of the year, animals may opt not to defend the area at that time. - However, it must be noted that many species do defend apparently valueless territories (e.g. through winter) in order to maintain ownership (in preparation for the next breeding season). - **Landmark influence:** - Physical features of the habitat (e.g. trees, ponds, hills etc.) determine shape and size. - As the landmarks change, so can territory size and shape. - For example, if landmarks are added to an area, the result is often more and smaller territories – i.e. a population increase. - The opposite is true if landmarks are removed. - (Consider the human impact on territories, with construction, cultivation, aforestation, deforestation etc.). ## How Are Territories Marked and Advertised? - It is essential that a territory must be advertised, in order for conspecifics to be aware of them. - This serves as a warning to potential intruders and limits unnecessary confrontations. - Advertising may be in the form of: - **Chemical marking:** scent-marking by means of urine, faeces, glandular secretions (from eg. pre-orbital, pedal, anal and inguinal glands). - **Visual advertising:** Specific movements along the periphery of the territory, aerial displays, posturing, object-horning, static-optic signals, marks on objects such as tree trunks etc. - **Vocal advertising:** Bird song, croaking, roaring, snorting, growling etc. - This is especially useful in areas where vision is limited. - There is usually a specific sound, song repertoire, volume or frequency used exclusively for territorial advertisement. ## Why is it Usually the Males that Hold and Defend Territories? - The reproductive success and dispersion of females are mostly limited by the availability of resources (more resources, more egg cells produced, or more frequent reproductive events or more likelihood of carrying young to term etc.). - The reproductive success of males, however, is limited by the access to females (more available females, more young fathered). - Therefore, it is usually the males that search for females and initiate courtship, often by competing for, and defending territories. - Territorial males gain access to females, either by: - Defending the females (often only in breeding season). - Defending the resources that attract females (often on a long term basis). ## How Many Females Can a Male Monopolize? - Males are better able to monopolize several females when they do not have to care for the offspring, when females have small home ranges and/or when females occur in small stable groups. - In such cases, males may defend very large groups of females (see harems later). - Otherwise, males are more likely to be monogamous or defend one female at a time. ## What Happens to Those Animals that Do Not Obtain Territories or Lose Them? - Depending on the species, these animals will either be pushed to suboptimal areas, where they may obtain inferior territories, or they may remain on the margins of the optimal areas, as floaters or sometimes in bachelor herds or as a coalition. - The benefit of this is that these animals are “closer to the action” on standby if a territory becomes available (an occupant dies), or to fight with the occupants and so reduce their fitness – even fighting together in a coalition to take over the territory and pride (lions), or even to help occupants defend their territories and in so doing gain experience and possibly inherit the territory (satellite males). - This adding of new breeding adults to a breeding population is termed recruitment. - Note that males who have lost territories will not find an alternative territory in suboptimal areas but will always attempt to regain their old territories. ## Territorial Behaviour in African Ungulates - In populations of African Ungulates displaying territorial behaviour, two to three animal components / groupings can be observed: 1. **Territorial Rams/Bulls** - These represent the best genetic material in the population. - In some species, territorial males are completely intolerant of other adult males in the territory. - In some cases, subsidiary males are tolerated and sometimes even allowed to assist with territory defense (see satellite males of waterbuck). 2. **Breeding Herds** - Consist of females and immature males. - These often have large home ranges. - During the breeding season, these herds move through the male territories, where they will either: - Spend time feeding and mate whilst there, then move on. - Mate with males of their choice and move on again – the territories provide no resources for them and they enter them for the exclusive purpose of mating – see lek system. - Be kept and defended by a male, sometimes for an extended period of time – harems (often very large groups of females). - Bachelor herds: Young adult males and old males that have lost territories. - They live on marginal areas and are used for recruitment. ## Ungulates Are Divided into Five Classes According to Territorial Behaviour - They all display one or more of the groups listed above: **Class A:** - Territories are held by pairs or individuals on a permanent basis. - Territories are small, cover almost the entire home range. - Scent-marking is done by means of dung heaps and infra-orbital glands. - These species are inconspicuous and will freeze or take cover when predators are close by. - They will only flee at the last moment. - Examples: Dik-dik, duiker, klipspringer, steenbok (all found in groups of 1-3) **Class B:** - Males attend breeding herds of females on a permanent basis. - Territories may cover the entire home range. - Bachelors are not in herds but are floaters, tolerated by the territorial male. - Scent-marking is done by means of faeces and glandular secretions. - These species are also inconspicuous and will mostly freeze or take cover when predators are close by. - Examples: Reedbuck, bushbuck, grysbok, vaalrhebuck (all found in groups of 1-12). **Class C:** - These territories are small compared to the home range and are sometimes only held in the breeding season. - Males use scent-marking (dung, urine and glands) but also visual and vocal signals to advertise their territories. - Non-territorial males are found in bachelor herds and are mostly not tolerated in territories. - Bachelor herds have a clear dominance hierarchy. - Female breeding herds (6 – 60 individuals) move through the territories of males. - In some cases, they may stay in a territory and are defended by the resident male. - Such female groups are termed harems. - Animals of this class do not take cover when predators are in the vicinity but are gregarious. - They send particular display signals to predators and flee when disturbed. - Examples: gazelles (springbok, impala), waterbuck, kudu, blesbok, bontebok. - Special cases in this class are the Uganda kob and fallow deer that display a lek system. - Small male territories are found in clusters. - The territories do not necessarily hold the best resources or any resources for that matter. - Females enter the territories for the prime purpose of mating and can therefore be very selective. - Males advertise their fitness (e.g. largest antlers). **Class D:** - This system is similar to C but may happen during migration. - The males defend zones around them and the females, rather than a specific site. - Marking is done by means of displays or dung. - Predator defense is done with large numbers and confusion of predators. - Examples: Wildebeest, hartebeest, eland. **Class E:** - Animals from this group do not have territories but do have a strict dominance hierarchy amongst the males. - The herds are very large. - Males stay in the herd for long periods but may on a seasonal basis move away and form bachelor herds (ensures protection of the habitat). - Predator defense includes mobbing of predators and social defense of vulnerable individuals. - Examples: Buffalo, gemsbok (oryx). ## Sociality and Social Groups - All mammals and birds show at least some social interaction when the mother bonds with her offspring. - However, “true sociality” in animals occurs when there is a clear social organization in a group of adults permanently living together. - In some cases, individuals struggle to survive without their group (e.g. baboons). - Social animals are highly interactive and there is a complicated communication system between them. - In some species, there is even regular specialized physical contact such as grooming in baboons. ### Theories for the Evolution of Social Groups: - One of these theories is that social groups are the result of delayed dispersal of offspring. - It seems likely that young may have had to stay with the natal group as a result of limited available territories. - As a result of increased competition for resources within a growing group, a distinct dominance hierarchy would have developed. - Since it is usually only the dominant individuals that reproduce, the genetic line of the group would have been protected. ### Delayed Dispersal of Young - Delayed dispersal of young is a common phenomenon amongst modern social groups. - For example, young female hyaenas and lions stay with their natal groups and only the males disperse (usually), whereas it is the young male wild dogs that stay and only the young females that disperse. - In the case of hyaenas and wild dogs, the cubs are raised in communal dens and in the case of wild dogs the entire pack assists with the care of the young (cooperative breeding). ### Examples of Social Groups: 1. **Troops, e.g. baboons:** - A troop consists of multiple males and females and their offspring. - Female ranking in the troop is inherited from the mother (matrilines). - Very complex interactions between individuals. 2. **Packs, e.g. wild dogs:** - A pack (the term used for social canids), consists of and alpha male and female and lesser ranked individuals (part of a linear hierarchy). 3. **Prides, e.g. lions:** - A pride consists of related females and their cubs and one or two males. - If two males, these are referred to as a coalition. 4. **Clans, e.g. hyaenas:** - The clan is ruled by an alpha female (the matriarch). - All females dominate males. - Very complex interactions between individuals. - Hyaenas generally compete more and cooperate less than any other social carnivore. ### Advantages of Social Groups: - Safety in numbers. - Finding a mate is easier (if allowed to mate). - Often assistance with caring for the young (provides more time and energy for the reproductive individuals to reproduce). - Overall more offspring are produced (as a result of point 2 and 3). - Protection of the family line also protects the genetic line. ### Disadvantages of Social Groups: - More competition for food and mates. - Some members may not be allowed to feed or mate (this is only an individual disadvantage and not a disadvantage for the group because it ensures genetic fitness). - Possibly more conspicuous and therefore more vulnerable to predation. - Greater spread of diseases. - Baboons have however turned this into a positive with their grooming rituals – greater bonding. - If communal dens are attacked, all young ones may be obliterated. - In some groups, infanticide is common (new dominant male or female may kill others' offspring). - However, can also be seen as an advantage because this ensures genetic fitness of the group. ## Mating Systems - The following mating systems can be distinguished: 1. **Monogamy (pair bond one male, one female)** - Pair bond can be long term or only in the breeding season. - A distinction is made between social monogamy (male and female living together) and genetic/sexual monogamy (male and female only reproducing with each other). - The latter is extremely rare, disproving the age-old belief that monogamous pairs are extremely loyal to each other. - Social monogamy mostly involves extra-pair copulations as common practice (e.g. aardwolf), where both the male and female mates with individuals from other pairs. - Monogamy probably developed in species because of limited or no other opportunities for mating and limited food availability (or sparsely distributed). - E.g. insectivorous birds are monogamous, probably because insects are difficult to find and one parent will have to stay at the nest while the other searches for food. - Also, males often abandon their females if more mating opportunities become available. - Monogamy is rare in mammals. Most examples are from terrestrial carnivores e.g. black-backed jackals, foxes, African wild dog (alpha pair) and aardwolf. - Monogamy is the predominant system in birds and usually associated with biparental care (see parental care). - In the case of monogamous birds bonding and courtship rituals are very important to establish partnership and coordinated rituals to maintain the partnership. - There is little to no sexual dimorphism in monogamous bird species, as females do not have to compare males to one another. - In most monogamous birds, males adopt behaviours to ensure their paternity. - E.g. in some species there is fierce protection of the female, whilst in others, where it is more difficult to protect the female all the time, males will copulate many times, thus swamping the sperm of any potential competitors. - In some bird species, e.g. some gulls and penguins, the need for a pair bond is so strong that, if one sex abandons or dies, the other will even form a bond with a same-sex partner, to brood the eggs and raise the young (gulls - female-female bonds develop, penguins – male-male bonds). - The purpose is still maximizing reproductive success, by ensuring that eggs hatch and offspring survive. 2. **Polygamy** - a. **Polygyny (pair bonds - one male, 2 or more females)** - This is common in birds and mammals, e.g. male lions with their pride of females, gazelle rams that defend a harem in their territories in the breeding season breeding season, and ostrich males that mate with more than one female, and helps to look after all their eggs. - Polygyny is often costly to females, because they have to share resources and the male's parenting. - But in most cases, they still accept it or even choose this system, because it is better than trying to search for an available male. - This system has been selected for through natural selection because males that can defend and mate with many females (and avoid predation) have the best genes and enhances the genetic fitness of the next generation. - b. **Polyandry (pair bonds - one female, 2 or more males)** - Very rare, e.g. jacanas, dunnocks, ducks, bandicoots, small lemur species. - Three types: serial (sequential) polyandry, simultaneous polyandry and cooperative simultaneous polyandry. - Serial polyandry is seen in the African jacana - the female takes turns to pair bond with the males and mate with them. She then leaves the male to brood the eggs and moves on to the next male. - Simultaneous polyandry is where the female pair bonds will all the males individually and lays eggs in separate nests and also broods them. - Cooperative simultaneous polyandry: the female mates with all the males and lays eggs in a single nest / clutch. All the males assist the female together and any one of the 3 can be the father – probably all three. - It is obviously beneficial to the female and her young (she gets protection and assistance with rearing of the young) but can it be beneficial to the males? - Only if their reproductive success is higher when sharing a female with another male. - Thus, continuous polyandry, particularly, is more likely to happen where environmental conditions are harsh and one male struggles to provide the necessary help by himself – two helpers are therefore better than one. - c. **Polygynandry (pair bonds - two or more females, two or more males)** - Also very rare but found in some birds, e.g. dunnocks, ducks and woodpeckers. - All males usually help all the females. 3. **Promiscuity (no pair bonds, female and male meet briefly to copulate)** - Common in mammals (e.g. elephants, chimpanzees, many solitary animals) and also in birds with a lek (e.g. birds of paradise). - A specialized type of promiscuity is found in lek systems, where males congregate and defend a display area (no resources), attracting females to him by specific display behaviours and exaggerated physical features (see sexual selection). - No bond is formed between the male and females. - Lek systems are not common in mammals. - Found in a few antelope (e.g. Uganda kob, red lechwe, tsessebe and topi) and all deer. ## Sexual Selection - This is a form of natural selection that favours features that increase an animal's chances of mating. - It often leads to marked differences between males and females (sexual dimorphism), resulting in female choice (intersexual selection) and also leads to strong competition within the same sex, usually amongst males, which is referred to as intrasexual selection. ### Intrasexual Selection - Competition amongst males, to “select” the winners, i.e. the dominant ones, who will then get access to females, either by holding territories or by being able to get closer to the females, or by getting the best position from where to display themselves to females (see intersexual selection for an explanation of the latter). - This competition may involve physical fighting or intimidation of opponents. - Winners will have, e.g., larger horns and tusks, more aggression, bigger bodies etc. This of course happens within limits, otherwise the feature would become too costly for the male (e.g. horns or body too heavy to function properly). - Competition may also involve methods to assure paternity (fatherhood), e.g. enlarged testes, larger ejaculate volumes, faster sperm, more frequent matings (sperm swamping), copulation locks, sperm plugs, sperm