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: ~:-;·:,t.. _._._ Inc 16..1 What Is an Ecosystem? Sf An individual organism is made up of many smaller systems that work together. Each system has a structure (its parts) and a function (what it does). This is true for cells, tissues, organs, organ systems, and the entire organism. In this section, you will learn how individual organisms are grouped into larger systems. Te~ How ecosystems are organized Ecosystems levels of organization An ecosystem is a group of organisms interacting with one another and their physical environment. Ecosystems can be as big as the ocean, or as small as a jar of water containing microscopic organisms. A Texas tall-grass prairie is an example of an ecosystem. A prairie ecosystem is made up of the plants, animals, and other organisms that live there, plus nonliving things such as soil, air, water, sunlight, and nutrients. The living and nonliving parts function together to remain in balance-similar to the way a single organism's parts work together to keep the organism alive. l + The diagram below shows the levels of organization of ecosystems. Individual organisms are grouped into populations. Populations of different species of organisms are grouped into communities. An ecosystem consists of a community of organisms and their physical environment. I I Ecosystem A community and its physical surround!ngs i i Oornmunity A group of different populations Population . ! .: A qroup of the ~am\3species i! ; .. : i Individual organism ! : . <. 386 .J) Unit 5 Organisms or ecosystem a group orgahi~rl)i interacting with one anpther and . their physical environm,ent I I i I i I Ii !~ I, 11 F If t! and Ecosystems /'.~, ~? -: i. ~j :t<';" IiW i~: Individual orqanlsms and species : ~pecies of the The first level of organization of an ecosystem is an individual organism Texas tallgra~s of a particular species. A species is a group of organisms that are capable I prairie . . of reproducing in order to produce fertile offspring. Fertile means "able to reproduce." A typical ecosystem contains individuals of many different species of animals, plants, and other types of organisms. For. instance, Texas tall-grass prairie ecosystems ~re dominated by plant life such as grasses and wildflowers. These plants provide food and shelter for many' animal species including snakes, small mammals, deer, birds, and a large variety of insects. The illustration below shows just a few of the many different species of organisms ~hat live in the prairie. ,- - '.-- i I ;-;" "~f6i spe(ies -'-la~r08P of or~-~~i!5m~ capable of reproducing fertile offspring Reading 16.1 What Isan Ecosystem? td produce 387 Corm Populations - 1:,·->:j.f.i;:._<;~~~· What is a A population is a group of individuals of the same species living in a given population? area. For example, a population of clover plants in a tray consists of the total number of plants in that tray. A population of clover plants in a field would be much larger (Figure 16.1).A typical ecosystem contains populations of different species including animals, plants, fungi, and bacteria. Growth rate Con p'op'Lliation~ a grou~~ofind:10r~ua" of the same species IiVir)9lna h'!;",! • given 'j'j' area growth r~te - the 7han;ge a population over time i :. J in size of I} ' '1 Anie: aic( Populations change as old members die and new members are born. In nature, populations often stay about the same size from year to year. Sometimes, though, populations grow or decline very fast. The change in size of a population over time is called its growth rate. Growth rates can be positive, negative, or neutral. The graph below shows data for a population of deer. What can you tell about the growth rate of this! population? Identify places on the graph where the growth rate is positive, negative, and neutral. ' Population abio 200 180 CfJ ~ 160 U 's '6 ~ 140 a 100 Q) 80 E 60 40 ::J •... .D ::J Z 120 I • 20 -( a o 5 10 15 20 25 30 35 40 env Time (years) Limits to In order to grow, a population needs energy, nutrients, and space. Energyj. population and nutrients both come from food. Therefore, population growth is limited growth by the amount of food available. Population growth is also limited by space. Different organisms require different amounts of space in which to live. If any of these variables are too limited, a population will not continue to grow. 388 Unit 5 Organisms ." .'r _-'. I: Figure 16.1: Each populdiion ofcfover plants consists of the number of plants in I : ! the group. , I ' I ;:', I, : and Ecosystems ~.. ''l' I i.l~!J~a : n I ··4 .~··:."7::,·,Jf<·:'f.": :·;~,""'i·'·~I'r:t\l¥f":"i8.1it'~·1l! ~i: ::t;!.-.. '~lf1.!1 '··~I~'r"'~".''i~"j.j;ir·'jf!,''1 1~,f~ t ~)~: .'n' ::gJ~ ~ft:?~,J.it~; Communities and ecosystems Communities i 'i~.1".;f. :il'iii'·.tr. ~1V~tai .;.<\ ,_ ~~ ~::}.i ·'!otH",g··,41·,: I,," :••,~.:,!\l}"'''''Hi A community is defined as all of the populations of different species in an ecosystem. Different species in a community interact with one another to obtain food. living space. and other resources in the ecosystem. To be considered a community, the different populations in an ecosystem must live close enough to interact with one another. i· I I!; '!¥,' ' ~~r"'!~''T :1~,;-,""111.1,,ji~1. ,I!! comm~nrty ~ all of tfle!Ropulations irl arlecosystem of dWfeteritspecies biotic factors - the' Ilvirg parts of an ecosystem incluclirg Individuals, populations, and communities i I An examplr.of In prairie ecosystems, grazing (plant-eating) animals such as deer. elk, and a commufjuty bison are. part of a community that depends on tall grasses for food and Ii I ! I shelter. Other animals in tl:iecommunity such as insects, rabbits, and mice also depend on the grasses for food and shelter. Animals such as coyote, fox, hawks, owls, and othef I birds eat some of the animals that feed off , ' the grasses. Microscopic bacteria that live in the soil are also important members of the community because they take nutrients from the air and make them available to the: grasses to help them grow (Figure 16.2). abiotic factors - the nonliving parts of an ecosystem inCluding temperature, sunlight, soil, water, and air I Biotic and Ecosystems are made up of communities and include living and nonliving bl . f ac~ors I parts. The living parts of an ecosystem are called biotic factors. These a lottc include individuals, populations of different species, communities, and their interactions. The nonliving parts of an ecosystem are called abiotic factors. These include temperature, sunlight, soil, water, and air. ! Changes in one or more abiotic and/or biotic factors result in changes to an ecosystem. organiJms and t~eir environments , Changes in any of these factors (amount of rainfall, decline in a population, overgrazing, e~ result in changes to other parts of the ecosystem. For example, a long period of scarce rainfall, or drought, may impact all parts of an ecosystem. Populations of plants that have low tolerance to drought may decline. Populations of animals that depend on those plants for food may also decline. Populations of drought-hardy plant species may increase as a result of the decrease in other plant populations. Grazing animals in a community may begin to depend on the drought-hardy species of plants for food. Figure 16.2: Bacteria that live in soil are important members of a prairie ecosystem community. Reading 16.1 What Is an Ecosystem? 389