T.G. Barnes, R.K. Heitschmidt, and L.W. Varner
Basic Habitat Needs of Wildlife
- Goals and Objectives
- Species Requirements
- Habitat Potential
- Species Interaction Effects
- Multi-Species Grazing Tactics
List of Tables and Figures
Historically, abundance of wildlife has been an important factor affecting humans' ability to meet the basic goal of survival. But as civilizations developed through the acquisition of knowledge, such as that which led to the development of a livestock industry, interest shifted from hunting to farming and ranching; thus, interest in wildlife declined. This decline continued in most developing societies until social and economic technological advances provided more leisure time and economic opportunities for pursuing such secondary goals as tranquility (see Chapter 9). Evidence of this increased interest is reflected in the relatively recent establishment of numerous wildlife preserves, game ranches, and fee hunting institutions.
Today, most wildlife species residing in regions supporting technologically advanced societies are considered to be of commercial, recreational, biological, aesthetic, and/or scientific value (King 1966). Currently, the most common measure of the value of any given wildlife species is related to sport hunting and/or aesthetic viewing. Land owners in many developed societies now find a substantial portion of their income is derived from hunting and aesthetic viewing enterprises (Glover and Conner 1988). Thus, a basic understanding of the potential interaction effects of a large number of sympatric herbivores is critical for the development of ecologically and economically sound livestock and/or wildlife enterprises.
Wildlife, in the broadest sense, includes all undomesticated animals. However, for the purposes of this chapter we focus on the broad ecological aspects of wildlife management as they relate to the management of large herbivores in grazed systems. Treatment is appropriately brief because the basic ecological principles and concepts of grazing management (see Chapter 1), animal nutrition (see Chapter 2), and grazing behavior (see Chapter 3) are equally applicable to all large herbivores whether they be domesticated livestock or undomesticated wildlife species. Likewise, at least the potential impacts of large herbivorous wildlife species on plant growth and development (see Chapter 4), ecological succession (see Chapter 5), and watershed condition (see Chapter 6) are similar to those of livestock. The major difference between the management of large herbivorous wildlife species and livestock in grazed ecosystems is related to differences in animal behavior. Generally, the temporal and spatial distribution of various kinds and numbers of livestock (see Chapter 7) are much easier to control than wildlife. This is because aggressive livestock breeding practices have historically focused on suppression of undesirable behavioral attributes. This is in contrast to most wildlife populations wherein natural selection processes have favored selection for a combination of traits that insure survival of the population over time. As such, some level of unconstrained behavioral attributes has been maintained in most wildlife populations. This is the major reason the management tactics employed in livestock-dominated enterprises differ from those employed in wildlife-dominated enterprises.
Basic Habitat Needs of Wildlife
Wildlife and domestic livestock share the same four basic needs: food, water, cover and space. Although the relative importance of these needs to the survival of an individual animal and/or population may vary, survival is a function primarily of the frequency that a limiting factor is encountered and its magnitude. A limiting factor is defined as a basic requirement that limits the size, growth, and/or quality of a wildlife population (Bailey 1984). Limiting factors vary over both time and space. For example, water may be the limiting factor when food is available and water is not, ,whereas food may be the limiting factor when water is available and food is not. In other words, any hierarchy of needs is dynamic in that it varies as a function of the changing attributes of the resident habitat relative to its ability to meet the changing needs of the animals present (Krebs and Davies 1984; Mangel and Clark 1986).
The major difference between the hierarchy of needs of wildlife and that of livestock is related to humans' ability to reduce the frequency of occurrence and magnitude of limiting factors. For example, in intensively managed livestock production systems, food requirements are met by adjusting livestock numbers (i.e., food remand; see Chapter 7) and/or by providing supplemental feeds. Likewise, water and cover requirements are met by constructing watering facilities and shelters, ,whereas space requirements are altered through redistribution of food, water, and/or cover over time and space. But these tasks are much more difficult to execute in extensively managed wildlife systems primarily because of the innate behavioral characteristics of most species. For example, number of animals is much more difficult to control because of the innate desire of most wildlife species to avoid detection and/or to escape from predators following detection. This is true regardless of whether the predator is human or some carnivorous wildlife species.
Ruminant wildlife species are selective consumers whose degree of selectivity ,varies depending upon morphological and physiological adaptations (see Chapter 2 and Chapter 3). In this sense, wildlife, like livestock, are commonly categorized as grass/roughage (e.g., bison, mouflon, oryx, and cattle), intermediate (e.g., elk, chamois, impala, and goat), and concentrate (e.g. white-tailed deer, moose, giraffe) feeders (see Chapter 2; Hofmann 1989).
The major factor affecting diet selection in most wildlife species is quantity and quality (i.e., nutritional value; see Chapter 2) of food available. This is evidenced by the fact that diet composition of any wildlife species varies over time (season) and space (location) in response to variations in quantity and quality of food available. For example, mule deer diets in north Texas have been shown to vary from 2-43% :browse, 0-5% grass, and 0-33% forb depending upon location and season (Fig. 8.1). This basic concept applies also to carnivorous wildlife species as evidenced in the Serengetti Plains wherein Bertram (1979) reported that "although lions feed on a number of the very large resident herbivores, such as buffalo and giraffe, which no other predator can take, they feed mainly on zebra and wildebeest when these migratory species are within their pride's area." Even the trophic level that wildlife species occupy in an ecosystem varies as a function of their morphological and physiological adaptations in concert with the quantity and quality of food available. For example, Rio Grande turkey in south Texas have been shown to act both as primary and secondary consumers (Fig. 8.2) with relative amounts of forage (ie., primary production) and insects (ie., secondary production) consumed varying as a function of seasonal availability.
In summary, it can be seen that the major factor affecting diet selection in most wildlife species is the quantity and quality of food available. Furthermore, it can be seen that the underlying ecological and biological principles that govern diet selection processes of wildlife species are similar to those governing livestock diet selection (see Chapter 2 and Chapter 3).
Water is an essential compound for the sustenance of all living organisms (see Chapter 6). Thus, availability of water over time and space is a critical factor affecting the growth and survival of all animal populations including both free-ranging wildlife and fenced livestock.
Water requirements of wildlife, in terms of both quantity and quality, vary widely among species. Differences are related to behavioral (e.g., nocturnal lifestyle), morphological (e.g., storage capacity, pelage type, thickness, and color), and physiological (e.g., proportional use of metabolic water) differences. As a result of these differences, some large herbivores can survive extended periods without consuming water (e.g., camel), whereas other species cannot. Moreover, because of these adaptations, required sources of water vary widely among species ranging from free-standing (i.e., streams, lakes, and reservoirs) to that pooled on the surface of plants (i.e., dew), and/or internally incorporated into vegetation (i.e., succulence).
The structural attributes of a habitat are embodied in the concept of cover as it pertains to the functional needs of animals (Dasmann 1981). This is evidenced in that some wildlife species use vegetative cover for escape purposes whereas others prefer habitats with little or no vegetative cover. For example, mule and white-tailed deer, javelina, impala, bushbuck, and mountain reedbuck often use moderate to dense stands of brush to either avoid detection by predators or to escape from predators following detection. This is in contrast to the cover requirements of such species as pronghorn antelope and blue wildebeest which prefer open grassland habitats because the structural attributes of such habitats (low or no vegetative cover) enhance these species' ability to descry predators from afar and to escape following detection if necessary.
Cover is perceived generally to be of greater importance to large herbivorous wildlife species than livestock because of its value as screening and escape habitat. It may be argued, however, that livestock would have a similar need for cover were it not for humans' continued efforts to protect livestock from natural predators through the employment of such tactics as lethal predator suppression and the penning and herding of vulnerable species. Evidence of domestic livestock-s inherent but latent need for cover is the tendency of feral livestock to preferentially inhabit dense stands of brush to avoid detection by their primary predator (i.e., humans) and/or to escape following detection.
Cover also benefits many wildlife species by virtue of its inherent ability to modify environmental conditions by providing shade during periods of high daytime temperatures and insulation during periods of low temperatures and high winds (thermal cover). In this sense, cover also benefits livestock particularly in the absence of man-made shelters (see Chapter 3).
There is also a strong interaction between vegetation cover and food in certain instances. For example, cover may directly enhance a herbivore's food supply if the primary cover species is a preferred forage (e.g., pricklypear cactus) of the resident herbivore (e.g., javelina) (Inglis 1985). Cover may also indirectly benefit certain species of herbivorous wildlife by creating a micro-environment that enhances the establishment and growth of certain preferred forages and/or by providing a structure that impedes the utilization of such species by competing herbivores.
Although animals require space to survive, amount of space required varies depending on the spatial distribution of food, water, and cover across a landscape and evolved behavioral attributes. The amount of inter- and intra-species space required by domestic livestock is almost exclusively a function of the space required to meet food, water, and cover needs. This is evidenced by the high level of livestock performance (i.e., growth) that is achieved in crowded finishing pens. In other words, space barriers do not appear to hinder livestock performance if sufficient food, water, and cover are available. A similar argument may be made for many wildlife species in terms of individual animal growth and survival as evidenced by their performance in zoos and wildlife parks. However, many of these same species require considerably greater amounts of space to achieve acceptable levels of reproductive performance whereby survival of a population is assured. This need may be viewed primarily as an evolved behavioral response, wherein space requirements (i.e., isolation) are linked to physiological function.
Much has been written about livestock-large herbivorous wildlife interactions in grazed systems (see e.g., Peak and Dalke 1982; Nelson 1984; Kie and Thomas 1988; Holechek et al. 1989), and it is not our intent herein to provide a detailed summary of this large, often site-, time-, and species-specific volume of knowledge. Rather, our objective is to present a conceptual model to assist in the development of an understanding of livestock-wildlife interactions regardless of location, time, or interacting species.
The model is structured around the basic premise, as presented earlier in this chapter, that livestock and wildlife have the same basic needs (i.e., food, water, cover, and space), and that relative performance in grazed systems varies in part as a function of the temporal and spatial distribution of various kinds and numbers of animals (see Chapter 7). By linking these two general concepts with specific knowledge about the ecology and biology of the interacting species, a management-oriented, decision- analysis model emerges (Fig. 8.3). The model follows the generalized decision model of Norton and Mumford (1 984) as presented by Scifres (1 987). It is composed of four broad components: goal setting, evaluation (steps A, B, C and D), action (step E),outcome.
Goals and Objectives
Goals reflect the desires of management (see Chapter 9), whereas evaluation assesses resource potential relative to meeting established goals (see Chapter 10). The establishment of realistic goals is often difficult because of basic misconceptions by management personnel (see Chapter 10). A common example of such in the management of livestock-wildlife grazing enterprises is the goal of maximizing both individual animal performance (e.g., trophy bucks, production per cow) and production per unit area of land. This is not an attainable goal in either wildlife or livestock production systems (see Chapter 7). Establishment of realistic goals is paramount in the development of any livestock-wildlife production enterprise, and the functional aspects of this planning model depend upon the establishment and continual assessment of management goals.
The objective of this step is to collectively garner all available information relative to the basic requirements of any particular species in terms of food, water, cover, and space. Such information is normally garnered from scientific studies and/or expert opinion based on observation and experience.
The objective of this step in the planning model is to assess the potential of the habitat of interest relative to meeting the four basic needs of the species of interest. This assessment is made separately for each species assuming no interaction effects. It requires an understanding of the temporal impact of various management tactics on ecological succession (see Chapter 4 and Chapter 5). The central question is: can the basic food, water, cover, and space requirements of the targeted species be adequately met within the habitat of interest in light of species requirements and established goals?
Effects The central objective of this step is to identify the magnitude of competitive overlap between two or more species relative to their ability to garner adequate resources to maintain desired population levels. Magnitude of competitive overlap varies among species depending upon a number of factors. For example, research in Oregon on pronghorn antelope, cattle, and feral horses (Figure 8.4) has shown dietary overlap is greater between cattle and feral horses than between pronghorn antelope and cattle or pronghorn antelope and feral horses. Similarly, research in the Acacia, Condalia, Prosopis dominated shrub regions of south Texas has shown dietary overlap between white-tailed deer and cattle is much greater than between either jackrabbits and white-tailed deer or jackrabbits and cattle (Figure 8.5). In similar studies, Bryant et al. (1979) found dietary overlap among white-tailed deer, sheep, and goats in the Prosopis, Juniperus, Quercus dominated savanna of central Texas was greater than between white-tailed deer and cattle, whereas Henke et al. (1988) showed dietary overlap between several exotic ruminants (i.e., axis deer, fallow deer, and blackbuck antelope) and cattle was much greater than between white-tailed deer and cattle. Moreover, all these studies showed that magnitude of dietary overlap varied over time (seasonally).
These example studies, as well as the results from a broad array of studies throughout the world, serve to emphasize that competition for food between livestock and herbivorous wildlife varies over time and space as a function of demand relative to the quantity and quality of forage available. In other words, the grazing pressure concepts as presented in Chapter 7 are as functionally sound in terms of wildlife management as they are in terms of livestock management. A similar argument may be made for water, cover, and space in that demand for each resource varies depending upon each species' requirements and resource availability.
The complexity of the model increases several fold at this step because it incorporates the concept that grazing management involves "the manipulation of grazing and browsing animals..." (Soc. Range Manage. 1989). It focuses on the direct, interaction effects of temporal and spatial distribution of various kinds and numbers of animals (see Chapter 7) on habitat attributes as they relate to the resource needs of the target herbivores. In essence, this step is designed to blend the functional aspects of steps A-C into an ecologically sound management plan in pursuit of established goals.
Number of Animals. Number of animals is the principal factor affecting livestock- wildlife interactions just as it is the principal factor affecting livestock production (see Chapter 7). This is so because of the direct impact number of animals has on total food, water, cover, and space demands and their subsequent availability. The magnitude of this impact varies depending upon degree of competitive overlap among the targeted herbivores and their associated behavioral traits. For example, research in the savanna regions of central Texas has shown that as livestock stocking rate increases, number of white-tailed deer decreases (Merrill et al. 1957; McMahan 1964; Reardon et al. 1978). Moreover, the magnitude of decline has been shown to vary depending upon the mix of livestock species present in that at equal rates of stocking, decline in deer numbers is greater in pastures stocked with sheep and goats than those stocked with cattle. This decline is largely attributed to greater dietary overlap between sheep, goats, and white-tailed deer than between cattle and white-tailed deer (Bryant et al. 1979; Blankenship et al. 1985).
Temporal Distribution. Temporal distribution of livestock also affects herbivorous wildlife populations. For example, research has shown livestock grazing at moderate intensities can, in some instances, enhance the quality and/or architectural structure of the forage available for subsequent grazing by wild herbivores such as elk and mule deer in North America (Anderson and Scherzinger 1975; Umess 1982) and Thompson's gazelle in Kenya (Blankenship and Overton 1974). Similar relationships have been shown between sympatric wildlife species such as black-tailed prairie dogs and bison (Coppock et al. 1983) and blue wildebeest, zebra, and Thompson's gazelle (McNaughton 1988), to name a few.
Spatial Distribution. Spatial distribution of livestock is an important factor affecting herbivorous wildlife populations. This has been demonstrated several times from studies showing white-tailed deer (Hood and Inglis 1974; Kramer 1979; Allred 1980; Cohen et al. 1989), elk (Skoviin et al. 1976), bighorn sheep (Morgan 1971; Gailizioli 1977), and moose (Denniston 1956; Schladwieler 1974) tend to vacate localized areas following introduction of livestock. Such behavior by these wild ungulates is interpreted generally to reflect an innate social intolerance to livestock since most species tend to return to the vacated areas shortly after the livestock are removed.
Firm level goals and objectives must be continually updated and modified as each step in the planning model is completed to insure the established goals are biologically realistic and attainable. Once the biological based planning phase of the analysis (i.e., two species) or series of analyses (al., more than two species) is completed (Fig. 8.3, steps A-D), the selected management tactics must be evaluated in light of availability of firm level resources such as capital, facilities, and labor (see Chapter 9). Likewise, it is critical that key output parameters be continually monitored following implementation to chart progress towards established goals (see Chapter 10). Such monitoring should be quantitative whenever possible (Kei and Thomas 1988) to insure that feedback into the goal assessment process accurately reflects movement towards or away from established goals.
A number of documents provide detailed descriptions of established techniques for monitoring key response variables in wildlife dominated ecosystems (Schemnitz 1980; Hays et al. 1981; Chambers and Brown 1983; Cook and Stubbendieck 1986; Kie md Thomas 1988). Described techniques are generally less precise than those utilized in livestock dominated enterprises because level of managerial control of the target wildlife species is Par less than that exercised in livestock production enterprises. Moreover, there is a need in most wildlife systems to monitor a greater number of interacting variables than in livestock systems. For example, the major factors effecting livestock production are food and water, whereas the successful establishment, continued propagation, and survival of most wildlife populations are often closely linked to cover and space as well as food and water. Furthermore, the relative impact of each factor on different wildlife species varies; thus the desired monitoring technique varies depending upon species. The step-wise ecological knowledge base derived from the employment of our suggested planning model is a prerequisite for selecting appropriate monitoring techniques.
The difficulty associated with the monitoring process in natural resource based systems is compounded further by the incorporation of the effects of time on the resource base (i.e., succession; see Chapter 4 and Chapter 5). Although the interaction effects of livestock on wildlife can be examined independently, they are in reality dynamic, multi-facet relationships that vary over time depending upon the targeted species and he habitat of residency. Two examples serve to emphasize this complexity. The first study centers on the observed increase in white-tailed deer populations in the savanna region of south Texas during the past century (Inglis et al. 1986). This increase is attributed primarily to a vegetational shift in the regional habitat from an open, grass dominated savanna complex to a woody shrub dominated complex. This seral shift is attributed generally to the interaction effects of intensive livestock , grazing and suppression of fire (Scifres 1980) against a backdrop of subtle climatic changes (see Chapter 5). As a result of this shift, white-tailed deer habitat has improved over time as measured by the increase in number of white-tailed deer.
Although all the precise reasons for this increase in the white-tailed deer population are unknown, there is little doubt all are related to changes in habitat quality in terms of resource availability. For example (Table 8.1), it has been shown generally hat quality of habitat for cattle has declined in terms of quantity and quality of available forage, remained neutral in terms of cover and space, and improved in terms of ,water. This is in contrast to white-tailed deer in that quality of habitat has improved in terms of food, water, and cover, and declined in terms of spatial needs. The changes in food and water are related to the shift from a grass dominated savanna to a shrub Dominated scrubland. Water development has enhanced the habitat for both cattle and white-tailed deer, whereas humans' physical presence, within itself (al., population density), is perceived to have reduced the overall quality of the habitat in terms of meeting the spatial needs of the white-tailed deer. However, when the effect of human presence is evaluated relative to the role played in altering the food, water, and cover attributes of the regional habitat, an entirely different perception emerges. Recognition of such simply serves to emphasize the complexity associated with the management of any natural resource including livestock-wildlife enterprises.
Another classic example of a time-related interaction effect has been reported by Walker et al. (1987). In this study, they reported water development on two South Africa game reserves generally enhanced wild ungulate populations during periods of average to above average rainfall. This increase in ungulate populations was the result of an increase in forage availability through spatial redistribution of the animals. However, they subsequently reported that during drought animal death losses were much greater than would have been expected in the absence of "improved" water development because of a general pre-drought depletion of forage reserves.
These two studies singularly and in combination reveal something of the complexity involved in any analysis of livestock-wildlife interactions. Both serve to emphasize that for any action there is a corresponding, multi-facet reaction, the value of which varies (i.e., positive, negative, neutral) over time depending upon management goals (see Chapter 10). These studies also reveal the universal applicability of the proposed planning model (Figure 8.3) in terms of species and location of interest. The model is as applicable to the management of avian species as it is to the management of wild ungulates. For example, bobwhite quail are a much studied (e.g., Rosene 1969; Lehmann 1984; Guthery 1986), economically important gamebird in many regions of the U.S., and specific knowledge of the basic needs of bobwhite quail (Figure 8.3, step A), their preferred habitat (step B), and the interaction effects of such (step C) and other wildlife and/or livestock species on bobwhite quail populations (step D) is a prerequisite for developing ecologically and economically sound management tactics to meet firm level goals. For example, bobwhite quail require a wide array of cover types for a wide array of activities including nesting (moderately dense grass- forb mixture), roosting (sparse, short-statured, open canopy), loafing (bare ground under elevated canopy), screening (low growing shrubs), escape (dense ground cover), dusting (bare ground), and thermal protection (dense ground cover under woody overstory). Although such needs are in some respects similar to the needs of many domestic and wild ungulates, they are also unique to bobwhite quail thereby demonstrating the need for specific knowledge about the needs of each species of interest.
Similarly, it is imperative that knowledge of habitat attributes be specific. For example, the spatial distribution of various habitats across a landscape is often a critical factor affecting wildlife populations. Knowledge of such effects is imbedded in the concept of edge effect which broadly refers to the impact that the spatial arrangement of various habitats may have on certain wildlife populations. Generally, the greater the number of habitat types or habitat boundaries (edges) present within an area, the greater the diversity and abundance of wildlife. Such is the case because many wildlife species require several types of habitat to meet their needs. As a result, the potential impact of a broad array of juxtapositioned habitats and their associated edges on targeted wildlife populations must be evaluated when implementing any landscape level management tactic.
Wildlife are important consumers in grazed systems. Their perceived role and subsequent value varies among societies depending upon societal goals. Wildlife and livestock share the same basic needs (food, water, cover, and space). Food habits vary among large herbivorous wildlife species in the same manner as livestock depending on morphological and physiological adaptations (see Chapter 2), behavioral attributes (see Chapter 3), and quantity and quality of food available (see Chapter 7). Similarly, because water is an essential compound for the sustenance of all organisms (see Chapter 6), all wildlife species require water, amount of which varies among species as a function of habitat of occupancy, activity, and evolved behavioral, morphological and physiological adaptations. Cover requirements vary among wild- life species depending upon desired use. However, cover requirements of large herbivorous wildlife species are functionally similar to livestock as evidenced by the manner in which feral livestock use cover. AU wildlife require space with the amount dependent primarily on the spatial distribution of food, water, and cover and secondarily on evolved behavioral attributes. Knowledge of the basic needs of targeted wildlife and livestock species in concert with knowledge of habitat attributes provides a basic foundation for implementing sound livestock-wildlife grazing management tactics.
List of Tables and Figures
Figure 8.1 Seasonal composition of mule deer diets at two locations in north Texas.
Figure 8.2 Seasonal composition of Rio Grande turkey diets in south Texas
Figure 8.3 Generalized decision-analysis model for assessment of potential livestock-wildlife interactions
Figure 8.4 Seasonal composition of pronghorn antelope, cattle, and ferral horses in Oregon.
Figure 8.5 Diet composition
during winter of co-exisitng black-tailed jackrabbits, white-tailed deer,
and cross-bred cows in south Texas
Table 8.1 Generalize effects
of change over past 50 years in south Texas habitat relative to basic needs
of cattle and white-tailed deer (negative, positive, and neutral.